Pennine Farmhouse marries traditional style with passive performance

Pennine Farmhouse marries traditional style with passive performance

Steel Farm is the first certified passive building in Northumberland, and the first cavity wall passive house in the north east of England. It is located near Hexham in the North Pennine area of outstanding natural beauty (AONB)

The design and construction of an exemplar Zero-Carbon Primary School

The design and construction of an exemplar Zero-Carbon Primary School

In 2008 the Department for Children, Schools and Families (DCSF) identified funding for pilot/exemplar projects under the Zero Carbon Task Force (ZCTF).

Delivering Low Energy Buildings for Real

Delivering Low Energy Buildings for Real

This Guide is a unique publication which combines professional guidance from a range of suppliers and industry experts, which, when combined together, can deliver a low energy building. A variety of systems are presented ranging from ventilation systems to a range of insulation, airtightness, windows and water treatment systems. 

Invisible Fuel

Invisible Fuel

The cheapest and cleanest energy choice of all is not to waste it. Progress on this has been striking yet the potential is still vast. Improvements in energy efficiency since the 1970s in 11 IEA member countries that keep the right kind of statistics (America, Australia, Britain, Denmark, Finland, France, Germany, Italy, Japan, the Netherlands and Sweden) saved the equivalent of 1.4 billion tonnes of oil in 2011, worth $743 billion.

BREEAM Environmental Assessment Method

BREEAM Environmental Assessment Method

BREEAM is the Building Research Establishment’s (BRE) Environmental Assessment Method first launched in the UK in 1990. It sets best practice standards for the environmental performance of buildings through design, specification, construction and operation.

The Full Monty (Zero-carbon, Passivhaus Primary School)

Montgomery Primary School in Devon is the UK's first zero carbon, climate – change ready school.  Andy Pearson takes a look at the fabric first, 'tea cosy' principles behind the design of this award-winning building.

When it comes to achieving outstanding results Montgomery Primary School, in Exeter, is top of the class. The UK's first zero-carbon school, it is also the country's first Passivhaus school and its first climate-change-ready school. If all that were not enough, this pioneering £8.9 m scheme was recognised by CIBSE at the Building Performance Awards 2014, at which it won the New Build Project of the Year award for schemes under £10m.

The zero-carbon target for the 420-pupil school was set by the client, Devon County Council, in 2008. The council had secured additional funding from the Priority School Building Programme - along with a grant from the Zero Carbon Task Force - to create an exemplar zero-carbon school that would help to increase knowledge and understanding of low-energy school design. The council worked with engineers Hamson JPA, and their architect and quantity surveyor affiliates at NPS Group, plus Exeter University's Centre for Energy and the Environment, to develop the design. The team set out to pioneer a new approach to primary school design. The simplest solution to meeting the client's zero-carbon aspirations would have been to construct a conventional Building Regulations-compliant building, which could be transformed into a zero-carbon solution using a biomass boiler for heat and hot water, and a green electricity tariff for electrical power. Such an approach was considered unsustainable by the design team.

'This solution is without value because it relies on the continued use of precious resources,' says the project's quantity surveyor, Chris Rea, from NPS Group. By contrast, Montgomery Primary School has been designed to minimise its use of resources, so that all energy for heating, lighting and power is generated on site.

“The space heating requirement of the school is now so small that the primary source of heat input is body heat from the pupils and teaching staff”

The starting point for the resource-lean design was to minimise fabric heat losses. The new two-storey school has been built within the grounds of the 1930s primary school it has now replaced. It is oriented north-south, with the majority of classrooms facing north and the more flexible teaching spaces to the south. A double height, central atrium-corridor divides the spaces.  Passivhaus standards were adopted for the design of the building fabric. These set a limit of 120 kWh/m' /year primary energy use, and 15 kWh/m'/year for heating and ventilation - significantly lower than the 55 kWh/m'/year for a typical school. To meet the heating target, the school's walls have been assembled from highly insulated, precast concrete sandwich panels, comprising 100 mm of high performance, rigid foam insulation, sandwiched between a 100 mm-thick concrete inner leaf and 70 mm outer skin.

Concrete was selected for its high thermal mass, which was deemed essential in enabling the step-up from Passivhaus to zero carbon. Pressure to complete the 2,786m2 building in time for the school term forced the design team along the precast, modular route. At the time the modular fabric solution was being developed, building services design was not sufficiently advanced to enable these to be incorporated into the precast units.

On top of the precast walls is precast concrete roof deck, blanketed with 200 mm of extruded polystyrene insulation. Underneath the building is a 150 mm layer of expanded polystyrene to insulate the cast, in-situ raft foundation and floor slab from the ground. 'We've adopted the same principle as a tea cosy, with insulation placed on the outside of the building to allow the thermal mass of the concrete structure to be fully exploited,' explains Rea.

Compliance with Passivhaus standards has ensured the school is exceptionally airtight. 'We followed the maxim "build tight, ventilate right",' says Rea. An air-seal barrier layer was defined in the modular wall, roof and floor constructions at the outset In addition, construction joints were carefully detailed and unavoidable service penetrations and other openings were kept as regular circles or rectangles to match the pipe or duct, and to make them easier to seal. To ensure the detailing was flawless, regular workshops were undertaken with all members of the construction team; for some of the more critical details, samples were prepared and tested on site to verify their performance.

The team's efforts were successful. The Passivhaus air-leakage standard is o.6 air changes per hour at 50 Pa; the focus on air tightness at Montgomery has enabled the building to achieve an impressive 0.28 air changes per hour at 50 Pa.

The fabric-first approach dramatically reduced the space heating requirement of the school. In fact, this is now so small that the primary source of heat input is body heat from the pupils and teaching staff.

A mechanical ventilation system with heat recovery ensures optimal thermal comfort is maintained throughout. Warmed fresh air is supplied to the teaching spaces. This returns to the air handling unit (AHU) through a high-level transfer grille into the building's central atrium-corridor, from where a high-level grille allows the air to return to the AHU in the plant room. This enables excess heat to be moved from high-occupancy spaces to spaces with a lower occupancy and a demand for heat.

Top-up heat is provided by electric heating elements mounted in the air supply ducts. The electric elements are set to operate on manual boost or fabric frost protection only. To protect against overuse, the boost feature is restricted to returning the room to the design set-point temperature. The advantage of this simple heating system is that it has zero losses when not in use and is almost 100% efficient in operation. 'Using electric heaters enabled us to offset this electricity using roof mounted photovoltaic panels.' says Rea.

The ventilation system operates in two modes. In winter, when heat is required, the building is predominantly mechanically ventilated using a variable air-volume strategy under control of the Building Energy Management System (BEMS). This uses temperature and C02 sensors to control dampers to alter the volume of air supplied. The BEMS also varies the speed of the fans in the building's AHU to minimise expended fan energy, while keeping the system in balance.

Energy consumption in the AHU is further minimised by a reversing regenerator unit. This uses two metal heat-exchanger packs to absorb heat from the exhaust air stream, and a series of dampers to reverse the airflow through the unit mechanically, once every minute. Initially, warmed exhaust air passes through one of the aluminium regenerator units, heating it before it is discharged. Simultaneously, cold supply air passes through the other, warmed, regenerator unit, where it picks up heat before it is supplied to the school. After 60 seconds, the control dampers reverse the airflow direction so that the regenerator warmed by the exhaust air now imparts heat to the incoming air, while its twin is regenerated by the warm exhaust air stream. The system is claimed to operate with 93% heat-recovery efficiency.

In summer, the building operates on a natural ventilation strategy. Each classroom has manually opening, triple-glazed windows that allow cool, fresh air to enter the room. This fresh air drives stale, warm air upwards to the transfer grille, and out into the central atrium-corridor, where large roof Iights open under control of the BM S to create a stack-driven, low-pressure, ventilation system. The effectiveness of the design was proven by modelling using IES: Virtual Environment software.

Summertime overheating of the highly insulated school is mitigated by the high thermal mass of the building fabric. In extreme circumstances, the natural ventilation system can operate overnight to remove excess heat to pre-cool the thermal mass for the following day.

In the same way that the building fabric was modularised, so too are the building services. Early involvement of the building services contractor, NG Bailey, enabled the ductwork and lighting assemblies to be supplied as modules and lifted into place. To reduce the lumen output of the lighting, the rooms all have light-coloured walls. In addition, absence detection and daylight sensors turn off lights in unoccupied spaces to minimise energy consumption.

On-site renewable sources are used to enable the school to meet the zero-carbon, in-use target Photovoltaic panels were found to be the most appropriate technology to meet the school's predicted 166,000 Wh/y energy requirement. Around 900 m' of Sanyo HIT N-235 SE10PV of PV panels are located on the south-facing pitch of the roof.  The electricity these generate is fed into the national grid.

Electricity generated by the PVs is not used to heat the hot water, although it is used for the trace-heating system, which keeps the water warm in the distribution pipe work. Instead, the hot water is heated throughout the year by a high-temperature, C02 air source heat pump, which picks up heat from the kitchen extract. Modelling showed this solution to have the lowest overall energy use of all possible options.

To enable the teaching and facilities staff to familiarise themselves with the innovative technologies and solutions employed at the school, the client specified an extended commissioning period in the contract. In addition, the team used the BSRIA Soft Landings approach for the handover and follow-up visits.

'The structure provided by this approach enabled the school staff, design team, client and contractor to work together to identify and resolve issues that - if left unsolved – would have compromised the school's low-energy operation and client's satisfaction with the scheme,' says Rea.

The design complies with the requirements of Building Bulletin 101: Ventilation of School Buildings. Unusually, the school has a 60-year design life. The scheme has been modelled by Exeter University and found to be sufficiently robust to ensure conditions remain comfortable, without overheating in the school, even as the climate changes up to 2080.

“The scheme is sufficiently robust to ensure conditions in the school remain comfortable. even as the climate changes up to 2080”

The scheme was completed in October 2011. Its measured energy performance figures are: 12 kWh/m'/year space heating and 167,358 kWh/ year total energy, including energy used in the kitchen. Despite these outstanding low-energy credentials the building has only managed a DEC band B because of its reliance on electricity for top-up heating. Monitoring has shown that, over the course of a year, the amount of electricity generated by the PVs is equal to that imported from the grid.

From the school's perspective, its carbon neutral performance means that the manager doesn't have to budget for heating and electricity costs over the coming year. Instead, any savings on the utility bills can be used to support future maintenance and educational budgets, to make the school a zero-carbon, self-sustainable, stand-alone environment of learning.

Pearson, A. (2014) ‘The full Monty’, CIBSE Journal, April 2014, pp. 4-8

A Beautiful Solution - An argument for Passive House by architect Justin Bere


The government's cynical recent energy policy announcements represent a dereliction of duty to the vulnerable and to future generations. There is an alternative, argues award-winning passive house architect Justin Bere - and it's beautiful.

Many of the UK's elderly citizens and low income residents cannot afford to maintain healthy conditions or basic levels of comfort in their homes, while those who are better off often cosset themselves in over-heated homes burning excessive amounts of precious and polluting fossil fuel. Everyone complains about the cost of energy, politicians wring their hands and try to sound as if they have a plan, but little is done to improve the UK's domestic and non-domestic buildings to make them more affordable to run.

"Those who peddle minor gestures in sustainability as if they are an al­ternative to passive house are either lacking in real knowledge, or simply playing confidence tricks on the public."

In a world where there is a rapidly growing population demanding a share of ever fewer resources, it is unrealistic folly and indeed utterly foolhardy to think that the answer to the high fuel consumption of our buildings is simply to outsource new power stations on guaranteed repayments to meet the unchecked projected future growth in demand. Yet this is exactly what the UK is currently doing. Through sloppy thinking, the UK is mortgaging the future; locking the younger generations into a level of expenditure on fuel that will most likely be completely unaffordable for them. Effectively they will be trapped in a situation with no affordable way out. What is utterly unforgiveable is that the reason for this is that the current generation doesn't want to feel any of the pain of transition. But transition will have to happen in the end and the longer we leave it, the more painful - or catastrophic - it will be.

Yet those of us in the passive house community have demonstrated that there is a solution that can deeply reduce overall energy demand in both new and existing buildings by 80 or 90% while at the same time creating ex­ceptionally healthy and comfortable buildings. New passive house buildings can be built for little or even no extra cost if design priorities are realigned with an energy saving imperative. But even where there are additional costs, such as in passive house retrofits, the costs can be paid back in a lifetime so that future generations are handed an affordable and beautiful solution.

The UK can look back with pride at how its population pulled together and responded effectively to national emergencies in the 20th century. Once again, and as much as at any time before, we need to respond with effective action to what I believe is an even bigger emergency than those faced by previous generations.

Effective action will include re-building the respect for vocational skills, the passion for making things to the best of our ability and to world-beating levels of excellence. It will include renewed respect for world-class engineers and engineering businesses. It will include a transformation of the construction industry from one focussed on what it can take from society, to one focussed on what it can give to society.

All this requires an honest, clear vision which I believe all of us in the passive house community have, and which we must promote. We must point out that those who peddle minor gestures in sustainability as if they are an alternative to passive house are either lacking in real knowledge, or simply playing confidence tricks on the public.

In An Introduction to Passive House (RIBA Publishing, £27.99), I present facts and arguments that attempt to show why passive house is the best form of building for people's health, comfort and general well being, for every age group, for fantastically low energy use, for very low whole-life costs, for the environment as a whole and for the future of the planet.

Embracing passive house technical methods does not mean that we have to turn our backs on beautiful architecture or light-filled, flowing spaces. Passive building techniques give us the opportunity to hold on to the uplifting aesthetic tenets of the very best 20th-century buildings, while at the same time transforming our technical abilities to make social progress and beauty possible in a world where excessive consumption is no longer tenable.

An Introduction to Passive House shows that the economics of passive house are clear. While shifting priorities is a simple lifestyle choice for many, for others the help of responsible, in­telligent and forward-looking govern­ments is needed in order to make it easy for individuals and organisations to make steps now, for the benefits of both themselves and of society at large, now and in the future.

Passive house is emphatically not a product, nor does it require designers to use particular products. The Passive House Institute offers manufacturers technical assistance to improve their products, and provides quality assurance certification, but passive house buildings can be built without any certified products. Passive house is a standard and an advanced method of designing buildings using the precision of building physics to ensure comfortable conditions and to deeply reduce energy costs. It does what national building regulations have tried to do. Passive house methods don't affect "buildability", yet they close the gap between design and performance and deliver a much higher standard of comfort and efficiency than government regulations, with all their good intentions, have managed to achieve.

The in-use performance data from passive house buildings shows that to provide comfort, to save energy, to reduce bills, to protect people from fuel poverty, to reduce excess winter deaths, to save money in the long run and, arguably most importantly, to reduce CO2 emissions, it is difficult to escape the conclusion that deep, energy-saving passive house retrofits and new-builds must become the norm. A deep, energy-saving retrofit programme will create jobs now at the same time as saving money on fuel imports, both now and long into the future. Vast amounts of money can also be saved by reducing the need for new power stations and for long-term storage of nuclear waste, and by reducing the serious impact upon the National Health Service of the UK's dreadful, damp and draughty buildings.

In concluding I will repeat the question that visitors to passive house buildings seem to ask more than any other: Why aren't all buildings built like this?

An Introduction to Passive House by Justin Bere (RIBA Publishing) is available now at RIBA Bookshops (

Bere, J. (2014) ‘A Beautiful Solution’, Passive House + , Issue 5, UK Edition, pp. 20.


Homage to Catalonia: A pre-fab straw bale Passive House 'first' for the region, by Oliver Style, ProGETIC

The Larixhaus is the first pre-fabricated straw bale passive house on the Iberian Peninsula. A project that took 7 months from start to finish, this single family home is located in the town of Collsuspina, Catalonia, Spain. Through careful bio-c1imatic design, thermal insulation with straw, an airtight envelope and high-performance windows, the Larixhaus has a projected space heating demand (calculated with PHPP) of 15kWh/m2 .a, approximately 80% less than that required by current Spanish building regulations. The project is a modest, but inspiring example of deep-green energy efficient construction, in preparation for the EU's 2020 deadline, when all newly built homes will need to be 'nearly zero energy'. Oliver Styles reports...

He huffed and he puffed...

Jordi, Itziar and their two daughters live in a small town in the hills above Barcelona, between rolling pine forests and burnt sienna escarpments. Renowned for its cool winters and even colder traditional stone houses, the area has been witness to one of the greener construction projects to have taken place in recent years south of the Pyrenees: the Larixhaus, Spain's first prefabricated straw bale and timber passive house. As straw bale building gains momentum in central Europe, with ground- breaking work from ModCell, White Design, LILAC and the University of Bath, the Larixhaus is a modest but determined example that timber and straw bale construction can move beyond the pigeon-hole of one-off self-builds and contend in the mainstream of beautiful, low-impact, energy efficient architecture. A simple, compact home which, despite the huffing and puffing of the big bad wolf, is set to brave the elements of this Mediterranean mountain region and place nearly zero energy construction on the map in preparation for the EU's 2020 deadline.

Early design: where the first steps count

The client's priority, from the outset, was to bring together a group of professionals with experience in timber and straw bale Passivhaus construction, who could design and build a small home at reasonable cost, where natural, renewable materials were married with a high level of energy efficiency and indoor comfort. In the early design stage, a simple and relatively compact building form was chosen, with 339m2 of thermal envelope enclosing a gross exterior volume of 437m3 over two floors, for a form factor of 0.78. The longest dimension of the building was aligned east-west, to provide maximum day lighting and reduce artificial lighting loads, resulting in a building aspect ratio of 1:1.3.

A location specific climate file was generated with the Meteonorm software and compared with the last 10 years of data from a weather station located 6km from the site, showing good agreement. Shading from nearby mountains was taken into account using a topographical horizon profile. The climate data was then entered into the PassivHaus Planning Package (PHPP) energy simulation and certification tool, for early stage design modelling and analysis.

Contrary to the orientation of all other homes of the street, the building's southern and most highly glazed facade was orientated perfectly south. PHPP modelling provided the required surface area of southern openings to take advantage of free solar heat gains in the winter. A combination of design strategies were modelled and tested for maintaining summer comfort with no active cooling.

To enjoy the spectacular views west to the jagged rock formations of Montserrat and east to the Montseny mountains, bedrooms are located on the ground floor, with a diaphanous kitchen, dining and living room space on the first floor. Wet rooms (bathroom and kitchen) are located in the same vertical plane, to reduce pipe runs and minimise heat losses in the domestic hot water system. To provide full fresh-air ventilation with minimal heat losses in the winter, a whole house ducted heat recovery ventilation system was chosen: careful early planning of duct routing made sure the duct lengths were kept to a minimum, reducing cost and energy losses. Operable windows on the east, north and western facades provide natural ventilation in the summer and sufficient natural light in all habitable rooms.

The skin: timber and straw bale

The timber superstructure and external cladding is PEFC certified, and was laser cut to order and delivered to the Farhaus workshop for prefabrication, 1 5km from site. The straw bales are 1200 mm x 700 mm x 400 mm, positioned vertically in the timber frame structure. The bales were sourced 1 25km away on the Costa Brava. The bales are enclosed on the outside with wood fibre breather board, followed by a 35mm ventilated gap and larch rain-screen cladding, fixed on timber battens. The ventilated wall reduces transmission heat gains in the summer and provides an exit for water vapour in the building structure - an important design consideration to avoid interstitial moisture build-up and condensation damage in straw bale construction. On the inside, the bales are shut in with 22mm formaldehyde-free OSB that acts as the air tight layer. Finally, Fermacell gypsum fibre board, over a service void, provides a dry-lined internal finish. Structural timber that spans the thermal envelope is thermally broken with cork insulation.

Two straw bale roof cassettes, with the bales positioned in the same direction as the walls, provide a thermally efficient roofing system, finished with clay tiles over a ventilated air gap, reducing transmission heat gains and summer overheating. Gravel infill on the intermediate floor adds some thermal inertia, although with the air-tightness and thermal insulation specification, combined with careful design of openings with external blinds, the building's thermal mass (calculated as 84Wh/K for every m2 of Treated Floor Area) was calculated as sufficient for maintaining summer comfort with natural ventilation. Given the site's altitude at 888m, peak summer temperatures are lower than coastal Mediterranean regions, averaging only 20°C in July and August. PH PP modelling showed that with no active cooling and a combination of glazing with a solar factor of 47%, external blinds on southern openings, and natural night ventilation, summer overheating frequency (when the indoor air temperature exceeds 25°C) could be kept below 3%, equivalent to a total of 36 hours in which the indoor ambient temperature rises above 25°C.

Despite not meeting the environmental criteria established between the client and design team, the most cost effective and thermally efficient solution for the floor slab was found to be 130mm of rigid polystyrene under the slab with perimeter insulation of 60mm around the edge of the slab.

The testing of alternative design strategies with PH PP modelling showed that an acceptable balance of heat gains and losses was achieved with triple glazing (with two low-e coatings, argon gas filling and TGI warm spacers), for a centre-pane U-value of 0.65W/m2.K and solar factor of 47%. Soft-wood Farhaus frames provide a U-value = 1.00W/m2.K, with cork insulation to reduce installation thermal bridges. The average installed window U-value is 1.06W/m2.K, not enough for cold' central European climates but sufficient in the Collsuspina climate to meet the comfort and hygiene requirements set by the Passivhaus standard.

The average weighted thermal transmittance of the building envelope is U-value = 0.21 1 W Im2K. The door blower test gave an impressive result of n50 = 0.32ACH (air changes per hour). Cold bridges were eliminated or reduced with modelling and optimisation in the design phase.

The building shell was prefabricated in the Farhaus workshop over a period of 6 weeks. It was divided into 10 separate modules, with the air tight layer and window frames installed and sealed. The modules were transported to site and the basic structure was assembled in two days. Pre-fabrication minimises on-site construction times, providing cost savings and near-zero on-site waste. The Larixhaus' embodied energy and C02 emissions derived from materials are minimised by prioritising natural, non-toxic, renewable materials with minimum processing (certified timber, locally sourced straw, cork, and gypsum fibre board).

Indoor air quality, acoustic comfort and active systems

Healthy indoor air quality is achieved through the use of non-toxic, Iow-VOC, natural materials. Exposed timber inside the home is either untreated or coated with water-based varnish. Healthy materials are combined with whole house ducted heat recovery ventilation to provide efficient, comfortable full fresh air ventilation during the winter. Cool air is brought into the home and pre-heated by outgoing stale air through a Passsivhaus Institut certified Zehnder Comfoair 350 ventilation unit, with an installed sensible heat recovery rate of 79%. PHPP simulations showed an average seasonal COP of 9. Efficient DC fan motors are essential for reducing electricity consumption: calculations showed that, given an average of 4,700 hours of operation per annum, at an air change rate of 0.40 (91 m3/h), the unit will consume only £31 of Spanish electricity each year (where household electricity is the 3rd most expensive in Europe). The ventilation unit is fixed on acoustically insulated mounts and located in the service cupboard by the entrance on the ground floor. Silencers on the indoor air supply and return ducts, combined with adequate duct sizing to control air velocities, means the system has a maximum measured sound pressure level of 33dB(A) in living spaces. The result is a quiet, discrete and efficient comfort ventilation system.

The near-zero heating demand is met by two low-cost 500W wall-mounted electric radiators in each bedroom, and one 450 W electric towel radiator in the bathroom. On the first floor, a 4kW air-tight log stove (that modulates down to 2kW) with a twin-walled concentric chimney flue, provides heat on very cold days, without compromising air tightness. Hot tap water is produced by a compact air-source heat pump unit with a COP of 3.75 (@ air = 15°C and water = 45°C) and a heat store of 300 litres. The air intake of the heat pump is located just above the stale air outlet of the ventilation unit, providing some performance improvement. The clients have set timing controls on the heat pump to make sure it does not activate between 1 1 pm and 8am in the winter, to avoid poor 'performance when outdoor air temperatures are low. Following 3 months of use, there has been sufficient hot water to meet daily demand with this control strategy.

Cooking is done on an induction ceramic cooktop with a re-circulation cooker hood. Artificial lighting is with LEDs and all white goods are A++. If the Spanish government decides, at some point in the future, to reverse the current legislation and encourage the use of renewable energy technologies rather than bending to the pressure of the large energy companies, the clients intend to install a grid-tied photovoltaic array to achieve a net zero energy balance. When the budgets allows, a rain water catchment system will follow suit (pre-installation was done during construction) .

Beyond PHPP and into the real world

A remote monitoring system will be installed in the coming months, providing quantitative data over a 2-year period, monitoring outdoor temperature and humidity, indoor temperature, humidity and C02 levels, together with electrical energy consumption for space heating, ventilation, hot tap water, lighting and equipment. It will be particularly interesting to see the in-use summer performance of the building.

Meanwhile, feedback to date from the clients shows that with outdoor night time temperatures reaching -1°C, indoor temperatures have remained above 20°C with no active heating, as long as there is some sun during the day. For successive days with no sun, they turn on the electric radiators for half an hour at night and in the morning, to maintain comfort. The first test of the log stove ended with Itziar opening the windows as it got too hot in the sitting room (!), confirming the PHPP calculated peak heating load requirement of 11 W 1m2. At least during this first mild winter, the stove seems largely redundant. The specific construction cost of the build has come in at around £1,005/m2, an estimated 14% more costly than building to current regulations in Spain. This gives an approximate simple payback time of just under 9 years, for a building with an expected useful life of 80 years.

So goes the story of the Larixhaus: a green-building homage to Catalonia and its rich history, number 10 in a growing list of healthy, comfortable, Passivhaus constructions south of the Pyrenees.

Oliver Style

Useful links:







Project team:

Client: Jordi Vinade, Itziar Pages

Architecture: Nacho Mart, Maria Molins, Oriol Mart.

Passivhaus design, PHPP analysis, M&E: Oliver Style, Vicenc Fulcara - ­ProGETIC SCP

Contractor: Albert Fargas - FARHAUS

5tructural Engineering: Manuel Garcfa Barbero - Klimark Architectural Consultant: Valentina Maini

Project Spec:

Energy standard: PassivHaus new build Location: ColIsuspina, Barcelona, Spain Treated floor area (PHPP): 92m2 Construction type: timber construction Completion date: December 2013 Completion time: 7 months

Space heating demand (PHPP): 15kWh/(m2a) 5pace cooling demand (PHPP): 3.2kWh/(m2a) Heating load (PHPP): 11W/m2

Cooling load (PHPP): 3.9W/m2

Primary energy requirement (PHPP): 96 kWh/(m2a) Construction costs (gross) [1m2]: 1211/m2

Air tightness (n50): 0.32ACH

Envelope information:

Exterior wall: U-value: 0.127 W/m2.K: in> out

  • 13mm plasterboard (Fermacell)
  • 35mm service void between timber battens at 8%
  • 22mm 05B 4 [air-tight layer]
  • 400mm straw bale insulation [052] between timber joists at 8%. thermally broken with cork insulation [040]
  • 16mm wood fibre breather board (DFP Kronolux) Wind tight membrane and ventilated larch rain screen cladding, flxed on external timber battens

Floor slab: U-value: 0.165 W/m2.K: bottom> top

  • 130mm XP5 insulation [034]
  • 350mm reinforced concrete floor slab
  • 80mm Pavaflex wood fibre insulation [038] between timber joists at 10 %
  • 22mm timber flooring
  • 60mm XP5 insulation [034] around the edge of the floor slab

Roof: U-value: 0.122W/m2.K: bottom> top

  • 15mm timber board (Fir) 22mm 05B 4 [air-tight layer]
  • 400mm straw bale insulation [052] between timber joists at 2% 16mm wood fibre breather board (DFP Kronolux)
  • Timber battens and roof tiles

Windows / doors

  • Farhaus, Fargas window frames
  • 50ft-wood laminated wooden window frames (90mm)

Uframe = 1.00W/m2.K

Average U- value window = 1.06W/m2.K

  • Triple glazing. with two low-e coatings and argon gas fllling; 33.2/16argon/4/16argon/4; TGI warm spacer

U-value glazing = 0.65W/m2.K

g-value = 47%

Entrance door - Farhaus: Fargas door

  • Triple glazed entrance door with identical speciflcation as windows

Udoor = 1.00 W/m2.K


  • Zehnder ComfoAir 350 Luxe
  • PHI certifled ducted whole house mechanical ventilation with sensible heat recovery
  • Distribution in HDPE 90mm pipes

Heating system

  • Ground floor: electric radiators
  • First floor: Rika Passiv blomass stove

Domestic hot water system

  • Theodoor Aerotermo 300 Plus
  • 3.6kW thermal compact air source heat pump unit, with backup electric immersion heater.

Oliver is a certified PassivHaus designer/energy consultant and co-founder of ProGETIC, an engineering practice based in Barcelona, Spain. He specialises in passive design and building performance optimisation through energy model­ling. He has an MsC with distinction in architecture, with the Centre of Alternative Technology and University of East London. He enjoys working closely with designers, developers, engineers and free thinkers who want to build or renovate beautiful, healthy, comfortable buildings with low running costs. - OSTYLE@PROGETIC.COM

Style, O. (2014) ‘Homage to Catalonia: A pre-fab straw bale passive house 'first' for the region’, Green Building Magazine, vol. 23, Spring 2014, pp. 20-24.


CREST Hub - South West College

The new CREST centre will comprise of three areas; the Hub, the Research & Development Lab and the Pavilion. The Pavilion will be newly developed while the Hub and Research & Development lab will be integrated into the existing Skills Centre building; with the work on the Hub area recently completed.  

The Hub will form the central office area within the CREST centre and will comprise modern office and meeting space where the CREST team will meet with companies to discuss their requirements and outline the services available.

From the very outset it was made clear that sustainable design was key to the successful completion of the entire CREST project, this responsible approach was to reflect the innovative aspirations of the CREST project.  We are pleased to be associated with our client, South West College, who are striving to create a sustainable centre that will form a benchmark for construction projects in the future.

The new pavilion project is the one of the most sustainable projects in the UK and will be the first commercial building in Ireland to have the following three sustainable credentials:

  1. Passivhaus Certified for Energy efficient envelope and ventilation system
  2. BREEAM excellent in terms of the BRE sustainable benchmark for UK commercials buildings
  3. The building will also be Carbon Neutral, this means that the building can provide, by renewable energy, it own source of heat and lighting.

Whilst a combination of these sustainable criteria has been attempted in other parts of the UK, this will be the first example in Northern Ireland or Ireland and will become a benchmark building for sustainability.

The Hub element of the project comprises of several meeting rooms, a waiting area, small kitchen and computer desk.  During the fit out of the Hub office area, where ever possible and feasible, recycled components and sustainably sourced materials where used.

A palette of recycled materials has been used to decorate the meeting rooms.  Bangor blue slates, reclaimed from the Belturbet Convent of Mercy (demolished in 2008) and reclaimed Florencecourt brick from a house in Enniskilen (demolished 2008) have been re used on the walls of the meeting rooms.  Pitch pine floor boards from the Belturbet Convent of Mercy have been used to differentiate the meeting rooms from the rest of the Hub.

The reception desk of the new hub has been created using the same pitch pine as has been used on the floors of the meeting room; the desk is supported on gabions of handpicked stone from the only slate quarry in Ireland.

The timber cladding used for the cladding walls in the Hub is reclaimed scaffolding boards that were used as shuttering on the A5 road extension project.  Scaffolding racks and poles are used to support the desks and other furniture that has been created bespoke for the project.

The palette of materials combined with the exposed duct work have created an industrial warehouse type aesthetic that is illuminated with low energy lamps to further increase the sustainability criteria.  The design utilises these materials to create a tactile, efficient and user friendly hub for a functional educational facility. The project was completed in February 2014.

Zero carbon targets and the construction industry

The new definiation of Zero Net carbon occurs after allowable solutions are introduced.

The new definiation of Zero Net carbon occurs after allowable solutions are introduced.

Zero carbon is great as a political aspiration but will it stack up effectively as a policy? Richard Hillyard examines Government aims to impose zero carbon targets on the construction industry. Back in July 2007 the Government published the Building a Greener Future statement. This policy document announced that all new build homes would be zero carbon from 2016.

The definition of zero carbon requires new dwellings to take into account:

  • emissions from space heating, ventilation, hot water and fixed lighting,
  • exports and imports from the development (and directly connected energy installations) to and from centralised energy networks.

Note:- Expected energy use from appliances is excluded from zero carbon definition.

By following this policy the Government expects new buildings to have net zero carbon emissions over the course of a year.

The definition of zero carbon consultation subsequently introduced by the government, sought views on the Government's proposals. This consultation ran from 17 December 2008 to 18 March 2009 and goes on to explain how to achieve net zero carbon emissions.

The Government also announced that from 2019 all non-domestic new builds will also be required to have zero net carbon emissions, with earlier dates for schools (2016) and public sector buildings (2018).

Wisely, the government set boundaries to what it meant by zero carbon. The embodied energy content of construction materials is not covered, and neither is the transportation of materials. Additionally, transport emissions associated with developments are not included as the government intends to deal with these through other policy instruments.

Given these omissions, it could be argued that Government's proposals do not equate to zero carbon. Even if it is not possible (nor cost-effective) to construct a building without generating any greenhouse gases, how far could we get by dramatically improving the efficiency and sustainability of construction methods?

In any case, does it really matter? Less than one per cent of the UK's existing building stock is replaced every year, and it's been estimated by the Department for Communities and Local Government (CLG) that 87 percent of the current housing stock will still be around in 2050. That means that the UK cannot meet its carbon reduction targets without a far-reaching retrofit programme for existing buildings.

The UK Green Building Council's proposal for a Code for Sustainable Buildings will play an important role in improving the focus on energy efficiency in existing buildings. But this is just one of a hierarchy of measures that the Government says will be needed.

The consultation document proposes a three-stage hierarchy for designers to achieve zero-carbon. The first step for energy efficiency requires compliance with Part L of the Building Regulations. This stage may also encompass other regulatory instruments, such as a mandatory requirement to design to Level 6 of the Code for Sustainable Homes.


The second stage proposed by Government is something called Carbon Compliance', which essentially is the use of on-site micro-energy generation. A report by the UK GBC Zero Carbon Definition Task Group believe over 80 per cent of homes in the UK to be unable to achieve zero carbon targets this way. The development of near-site and off-site low and zero-carbon energy generation is also being proposed.

Initially there were reservations over whether the use of biomass technologies could be included in the zero carbon strategy. However, the government appears to be in full support of using biomass systems both within new homes and as a source of direct heat from nearby off-site generation.

The third stage in the zero-carbon strategy is what is known as ‘allowable solutions', which is a buy-out fund or form of carbon offsetting through high quality international investment in low and zero carbon projects.

This third way will, it is believed, only be permitted where energy efficiency and carbon compliance are unable to be achieved totally through on-site and near-site measures achieve the goal of zero carbon - in other words the residual emissions.

The government is proposing a system of credits to permit off-setting to occur. Credits will be awarded to developments that have a range of energy-saving criteria. For example, energy-saving appliances and low and zero-carbon technology capable of exporting energy to the grid will earn credits to enable an offset of residual carbon emissions.

The government would prefer off-site low and zero carbon technologies to be included in this part of the hierarchy by feeding into the national grid.

So will the policy work? The first two parts of the hierarchy - energy efficiency and carbon compliance - are signs of forward thinking. With a few tweaks, off-site low and zero carbon energy generation could play an integral part of reaching the zero carbon target, but only if the contribution from the grid can be guaranteed to be clean.

Other questions remain to be answered. For example, with allowable solutions, will off-setting contribute to reducing carbon dioxide emissions enough for claims of zero carbon to stack up - not just initially but over a sustained period? Or is it, as some might argue, just a way of covering up holes in the system, and easing collective guilt?

Off-site low and zero carbon energy generation technologies sounds like reasonable measures, but if they are supplying to the grid as opposed to supplying directly to a development, what guarantees will there be that this clean energy will not be lost in the overall electricity generation? This is a key issue, especially when it's mixed with the output from the proposed eight new coal power stations (each potentially generating eight million tonnes of CO2 per year) that the Government is keen to build.

These questions highlight the credibility gaps that still exist between intention and delivery in Government's push for a low carbon and sustainable energy future. Whatever transpires following the zero-carbon consultation, tackling the issue effectively will not only significantly affect the environment, but also our pockets.

Zero carbon targets on the construction industry, [Online], Available: [18 March 2014].

Quality assured Passivhaus buildings: It's more than a number – Part 2

Mark Siddall of Low Energy Architectural Practice:  LEAP

Mark Siddall of
Low Energy Architectural Practice: LEAP

In part two of his two part article on quality assured Passivhaus buildings, Mark Siddall [], who specialises in sustainable building design, explains the certification process in a little more detail.

In the last article I explained that the Passivhaus standard is much more than an energy performance standard, it is also a quality assurance standard that closes the gap between theoretical performance and reality. I also highlighted the importance of using the appropriate design tool (the Passivhaus Planning Package) when designing Passivhaus buildings, and I discussed the ways in which buildings that are not subject to the same quality assurance system have been found to fail to satisfy their performance targets.

In this article I will discuss the accreditation of approved certifiers, Passivhaus designers, products and buildings and the fact that, in order to assist with delivery of its Passivhaus projects, Devereux Architects has developed a stringent quality assurance methodology known as the Passivhaus Delivery System. To assist with the dissemination of the lessons that the practice has learned, it is to become a founding member of the Passivhaus Buildings Trust, a new organisation established by the AECB and committed to assisting the UK with the delivery of buildings that perform as intended.

Approved certifiers

The Passivhaus Institute regulates who is able to certify Passivhaus buildings. In order to become an approved certifier, applicants must work at the Passivhaus Institute for two weeks undertaking training and checking proposed Passivhaus designs. Currently there are four approved certifiers in the UK. Peer review, a well respected tradition in academic circles, serves to ensure errors are eliminated and that quality is maintained.

One of the issues that can put people off the certification process is the cost, particularly if it means that dual certification is required; say Passivhaus and Code for Sustainable Homes. In this respect the risks need to be weighed against the losses. Do you want to achieve the carbon reductions in theory or in practice? Do you want to be exposed to claims of negligence or not?

If the designer has not built a Passivhaus of your building typology before, albeit a house, school, hospital or office, then they may not have an adequate quality assurance system. For this reason I would tend to offer a cautionary note and would suggest that certification is a wise choice, after all you want to be sure that you're getting the energy and carbon savings that you are paying for.

If, as a client, you employ a certified Passivhaus designer you can be assured that they have a certain level of competency, certainly higher than average; but once again if they have not delivered a Passivhaus they may not yet have all the tools in place. Perhaps, in this case, a client could proceed at risk and decide that there is no need to go through the certification process, but ultimately certification is the surest way of ensuring success.

Experiences at the Passivhaus Institute (PHI) have shown that the certification process can actually serve to focus the attention of the design team and can, with a little coaching, actually end up a lot less complex whilst also achieving the end goal. In this respect the certified buildings become less expensive than would otherwise have been the case; so in essence certification more than pays for itself.

Certified Passivhaus designers

There are two means by which a designer can become a certified Passivhaus designer. The first is to build two Passivhaus buildings and get them certified. This is a particularly challenging approach but has been achieved. Until recently it was the principle method of proof (in fact it was the initial approach that I embarked upon and, given the paucity of information in the English language, required a great deal of research). However, of late the Passivhaus Institute has established a training course to allow people to become certified Passivhaus designers (I attended the first UK course late last year). The intensive ten day training course covers the design and specification of the building fabric, ventilation, heating and of the requirements of the standard. The course is then followed by a rigorous three hour exam.

If a client desires a Passivhaus building there is no technical requirement to employ a certified Passivhaus designer, However, there are distinct advantages insofar as they have proven that they have the basic knowledge and the skills. Having passed an exam should not of course be confused with experience, and ultimately experience is the surest way to avoid any of the pitfalls that can catch the Passivhaus designer unaware.

Certified designers can, dependent upon their background, contribute to a project by undertaking the design first hand or by coaching a less experienced design team. An experienced certified designer, or a certifier for that matter, can help to streamline the design, avoid abortive work and advise upon optimisation of the design and construction process. By undertaking these roles they can assist with the delivery of robust solutions and help to minimise, and even reduce, both the capital and the running costs without compromising the ambition of the project.

Certified components

Passivhaus certified components can be recognised by the use of the Passivhaus Institute logo. Components include windows and ventilation heat recovery systems. The first, and most reasonable, question that can, and should, be raised is, is there a need for certified components? You could say that the unfortunate answer is 'yes'. Let's take a look at the reasons why each of these components require certification.


The Passivhaus standard requires that windows have a whole window U-value of 0.8W /m2K. The thermal performance requirement is not a whimsical number. Like everything in Passivhaus design it is supported by an understanding of building physics and the desire to satisfy human comfort requirements under a given set of design conditions. The whole window U-value has to be calculated in accordance with EN 10077 and includes the frame, the spacer bar and the glazing. Furthermore when designing a Passivhaus, using PHPP, the thermal performance of each window component must also be considered - experience has shown that such data is not readily available from most manufacturers and suppliers. Certification makes sure that manufacturers have such information available and that it was verified.

Provided the design parameters that underpin the U­-value requirement are met, with sufficient knowledge and understanding of building physics, it is possible to design certified Passivhaus buildings without using certified windows. In theory this can save money. However if the manufacturer is not familiar with Passivhaus and can not readily provide the supporting data, this process can be more trouble than it is worth as the design fee is likely to increase to cover the additional workload. There is a nice little anecdote to support this. Some years ago, at the 7th International Passivhaus Conference, one lecturer presented analysis that suggested the best option for reducing costs was not to use Passivhaus certified windows. A year later the same lecturer came to the conference to present his views about Passivhaus design. The difference was that this time, now that he had a little more experience and had worked on a couple of Passivhaus buildings in Vienna, his message was now "Only use certified windows! All the other stuff is substandard. And it's difficult and expensive to check!"

Heat recovery ventilation (HRV):

Compared to windows it is more difficult to avoid the need for certified heat recovery ventilation (HRV). One of the reasons for this is the fact that glazing systems can be thoroughly specified by the designer and can then be batch processed by the manufacturer on a project by project basis. The same design flexibility is not available with heat recovery systems for, whilst they are relatively simple components, their design relies upon a great deal of careful and skilful engineering.

The Passivhaus Institute uses a different testing procedure to that described in EN 13141 (Ventilation for Buildings) - the standard which is used for SAP Appendix Q assessment. The reason for this alternative testing method stems from the fact that when the Passivhaus Institute (PHI) started their research they found that air could leak from one side of the heat exchanger to the other. This not only inhibits the thermal performance of the heat recovery system but also compromises thermal comfort as the supply air is colder than comfort standards would recommend. The PHI also recognised that the thermal envelope should be described in a realistic manner, i.e. what is really needed is the performance of the heat recovery unit in a building and not in a laboratory - something that the EN standard also fails to do.

Passivhaus design

When the PHI undertook lab tests and ran through the physics they found that there was, on average, a 12% difference between the calculated performance using the EN standard method and monitored values based upon the PHI's alternative method. In effect the EN standard overestimates the performance of heat recovery units because it counts losses from the laboratory and into the exchanger as if they were heat gains, and because it does not properly account for air leakage within the unit - which are again incorrectly treated as gains. Worryingly, on the basis of recent on-site measurements from installed but uncertified HRV units, Dr. Rainer Pfluger from the University of Innsbruck reports that, the differences in performance can be even more extreme.

For a worked example I'll take two HRV systems, one Passivhaus certified and one EN tested. For convenience both have an apparent efficiency, of say 87%. Using the EN tested unit in a building, rather than a laboratory, it has an efficiency of about 75% in the specific case. I then tested these two units on a Passivhaus modelled in PHPP and found that the house using the EN tested unit, would consume about 25% more energy than the Passivhaus certified unit. (If you were to address energy performance deficit, by improving the opaque thermal envelope alone, you would need about 125mm more insulation!)

Delivering Passivhaus buildings

Stating what is required for the delivery of a Passivhaus, at the first Passivhaus Schools conference, former Deputy Chief at the Energy Department of Frankfurt, Axel Bretzke said; "You need architects and other design team members with an obsession for good quality, simple and creative solutions, a knowledge of building physics and some prior experience of energy efficient buildings". From this statement it can be appreciated that a Certified Passivhaus is greater than the sum of its parts and is only made possible by employing the right people, and quality assurance tools, and having a thorough understanding of the requirements. Sadly it is here that the supposed 'Passivhaus' buildings that were discussed in the previous article seem to fail.


For the last eighteen months I have been working with our client, Gentoo Homes, on a residential development that incorporates 25 Passivhaus standard homes at the Racecourse Estate, Sunderland. From day one we have worked very closely with Alan Clarke, our energy and services engineer, to develop the design. This close working relationship has been instrumental in our ability to get this far. Judging by my experience to date, and having recently completed the first English language version of the certified Passivhaus designer course, I have reached the personal conclusion that, whilst the course is pretty robust, it does not yet take into account the quirks of the UK building industry; as a consequence there is still a potential knowledge gap, albeit much reduced, between theory and practice. It is for this reason that Devereux Architects has undertaken an extensive three year research programme and developed its own Passivhaus delivery (PHD) system.

If this gap is to be bridged on a large scale there is still a substantial amount of desktop research that is required before being able to realistically deliver a certified Passivhaus that performs as intended. For instance, there are a few scant scientific reports on the phenomenon of thermal bypass - unaddressed heat loss can increase by over 150% - and very little information on delivering truly airtight buildings. With this in mind my last few years of painstaking investigation, which now forms a part of the PHD, should be sufficient. I am looking forward to learning about how the buildings perform in reality - as they are to be studied by the EST and the Good Homes Alliance, time will tell whether all the efforts have paid off and whether we have succeeded in delivering a Passivhaus.


The Passivhaus delivery (PHD) system is a totally new kind of quality assurance system that is focussed upon delivering low energy buildings. The operating procedure has a number of phases. The first phase occurs during the briefing process. Here we deliver and facilitate Passivhaus workshops to improve the understanding by the client and the design team.

During this process we raise general awareness of what it means to procure a Passivhaus building and highlight the fact that some new approaches to brief development are required. The second phase occurs during the tendering process, here we run a workshop to inform the contractor about Passivhaus, the requirements that it places upon the scheme and we also work to dismiss a lot of myths about buildability (if the project is being managed through a partnering process or as design and build contract, this workshop may occur earlier in the process). The third phase occurs post tender. Here we provide workshops to the contractor's project manager and the sub-trades.

Our system also includes a new quality assurance tool, the purpose of which is to assist the construction supervisor and the site staff with ensuring that the buildings are constructed to the required standards. The quality assurance process also includes the requirement for the commissioning of heat recovery systems and heating systems. In addition to this we also require that the construction supervisor reports any deviations from the design drawings so that we can assess the impact upon the buildings performance - this process is critical as workmanship can make or break the scheme.

The purpose of this exercise is to assist the contractor with ensuring that the building is constructed in the appropriate manner. Whilst the project is on site we regularly inspect the site and photographically record the progress of the work, to address specific concerns, and we continue training for each new sub-trade that arrives on site and find design solutions to any unresolved issues.

During the first year or two the systems begin to bed down and settle in. They can have a tendency to begin to drift away from their settings, and whilst certain gremlins come to light, others can go undetected for years - decades even. Seasonal commissioning should be a necessary part of the annual maintenance schedule. Strictly speaking, this particular process lies outside of the requirements of the Passivhaus standard - but it is not outside the recommended approach to quality assurance. After all, which building owner would, after having made a substantial capital investment, willingly turn their back on it and then squander money on the energy bills that they had sought to mitigate? In buildings it is import to ensure regular maintenance is undertaken. There are a growing number of proven strategies for delivering successful long term building maintenance - once again these are reviewed as a part of Devereux's PHD system.

Post construction

In order to help ensure that the building will perform well in reality, aspects of human behaviour and building usage must also be considered. For this reason the role of the PHD continues beyond the construction phase and engages with building occupants, maintenance personnel and facilities managers. Once again workshops are used to inform people about the new building and how they can get the most out of it. Building occupants are briefed about the control systems for thermal comfort, lighting and acoustics whilst the people that manage the building (which may or may not be the occupant) are briefed about maintenance schedules and the like. To ensure that these valuable lessons are not, in time, forgotten, two simple manuals are prepared that explain the key features, facts and requirements of the building.

It should be recognised that the focus of the PHD differs between non-domestic buildings and residential ones. The reasons for this change of tack are that non­domestic buildings tend to be larger and more complex - thus requiring greater explanation and understanding, and also the fact that non-energy considerations can have a substantial impact upon the total lifecycle cost of operations - often even greater than that of the energy costs. It is apparent here that the interest, as with most good Passivhaus, is in providing multiple benefits from single expenditures.

Is it necessary to certify a Passivhaus building?

At the start of this article I ventured to suggest that the only real Passivhaus is a certified Passivhaus. Strictly speaking this may not be the case, provided that certain assurances are in place. For example, as fellow AECB member Nick Grant of Elemental Solutions explains; "If a Passivhaus building is not to be certified one party or another must be willing to stand by the claim if challenged; this may be the architect, a clerk of the works or the constructor". For example a person buying a home described as a 'low energy eco-building' could expect high levels of comfort and low energy bills. However, if they find that the building uses more fuel than expected, and because in the UK 'low energy eco-building' is not an established performance standard, they would have little foundation for a claim (like the German 'low energy' homes from the 198O's, some so called eco-buildings are unable to achieve comfortable temperatures in cold weather). If this building had been described as Passivhaus the owner could ask to see the PHPP calculations, the results from the blower door test, construction details and specifications.

If these documents were in order then further investigation could be carried out. It may suggest that the owner could be enjoying a higher than normal indoor temperature or may be leaving windows open all winter. If this is denied then it should be a relatively simple matter to determine whether or not the building has been constructed appropriately, even if it would be too difficult to identify exactly where the heat is being lost.

Passivhaus Buildings Trust

Due to differences between certain UK and German national standards, and differences in construction technologies, there is a need for a platform, a centre for excellence that can assist with the integration, coordination and delivery of the Passivhaus standard within the UK context. Such a platform would also ensure that the quality of the Passivhaus standard is not compromised. To assist with these integration issues such a platform has now been established by the AECB, the Passivhaus Buildings Trust. This not-for-profit organisation will work for the public good and recognises that reducing energy use and carbon emissions from the UK's buildings is a major challenge. The Passivhaus Buildings Trust aims to:

• Be a centre of excellence for information, knowledge and skills.

• Develop accreditation schemes for individuals,

companies, products and services which can deliver low energy buildings.

• Help to generate flagship low carbon developments throughout the UK.

• Assist with the coordination of approved certifiers and to certify Passivhaus buildings.

The rapid introduction of the knowledge, skills and products to deliver low energy, low carbon buildings requires focused leadership. For a number of years Devereux Architects has had an interest in promoting the low energy, low carbon agenda. The practice is proud to announce that it is to become a founding member of the Passivhaus Buildings Trust.


In this series of articles I have identified, and then clarified the reasons for, the chain of quality assurance mechanisms that run throughout the Passivhaus certification and delivery process. Each one is necessary; each one is a critical link in the chain. I hope that the next time you read an article on a building that is claiming to be, or perhaps need to make a decision about procuring, a Passivhaus you will be able to ask yourself a few questions and determine whether or not the project could really be what it says it is.

Accessed online: 7th August 2014

Quality assured Passivhaus buildings - Part 1

Mark Siddall of Low Energy Architectural Practice:  LEAP

Mark Siddall of
Low Energy Architectural Practice: LEAP

In part 1 of a 2 part article, Mark Siddall of Low Energy Architectural Practice: LEAP  [ ] observes that there appears to be mounting confusion about the Passivhaus standard and Passivhaus Certification. Here he reflects upon the implications of such misunderstandings. It’s time to straighten out some the facts. The government has undertaken a legal commitment to reduce carbon emissions by 80% by 2050 and is developing tools and strategies to try and ensure that this commitment is satisfied. This has led to the rise of  the Code for Sustainable Homes and a series of net- zero carbon targets for new build projects - whereby homes are to be net-zero carbon by 2016; schools and pubic buildings by 2018; and commercial buildings by 2019. However, recent research by Leeds Metropolitan University has found that homes built to energy performance standards, including Building Regulations, are not performing as required. This fact alone raises some important concerns. Quality assured Passivhaus buildings have been proven to perform in accordance with theory. However, in the UK, there are growing number of projects that people claim to be Passivhaus buildings but upon closer analysis do not appear to satisfy the rigorous quality assurance requirements established by the Passivhaus standard. This introduces risks that could damage the growing reputation of the standard before it has been properly established.

A quick recap

In case you didn't know, the Passivhaus standard, is the world's leading energy efficiency standard and it can be applied to all manner of building typologies including homes, offices, schools, care homes etc. Of late I've been to a number of meetings and conferences where it has emerged that people tend to think that the Passivhaus standard is 'a number' or perhaps a series of 'energy performance parameters.'

The basic, well publicised, performance requirements that tend to be recited include:

• an annual energy consumption for space heating of s 15kWh/m2.yr

• a primary energy requirement of less than 120kWh/ m².yr (best practice being less than70kWh/m2.yr)

• an air leakage of less than O.6ach@50pa when tested in accordance with EN 13829

• perhaps they are also aware that the risk of overheating should be s 10% (with best practice being less than 5%).

What is not recognised in these statements is the background to these standards. Supporting these basic requirements are a number of other, less widely

appreciated requirements that serve to deliver thermal comfort and energy performance, all via a carefully structured quality assurance system.

Towards a need for quality assured buildings

Rather than discuss the process of delivering low energy buildings, people seem to have a fascination with design targets. The question is, do these targets turn into a reality? When asked how he got involved in working on low energy buildings, Dr Wolfgang Feist, founder of the Passivhaus Institut (PHI) said; "I was working as a physicist. I read that the construction industry had experimented with adding insulation to new buildings and that energy consumption had failed to reduce. This offended me - it was counter to the basic laws of physics. I knew that they must be doing something wrong. So I made it my mission to find out what, and to establish what was needed to do it right."

In this respect I personally find the above statement by Dr Feist rather intriguing for it indicates to me that in Germany, just as the UK, quality assurance is key to the delivery of truly low energy buildings.

In the context of a Passivhaus building, what is meant by 'quality assurance' needs to be clearly understood. Here it includes the correct building physics concepts,

the correct application of these concepts during design and specification processes and finally the correct implementation on site. Various aspects of these quality assurance issues will be considered in more detail below, but first it is useful to provide a little background as to why this quality assurance is required. A little bit of history will serve to make a point.

The history of the low energy standard

In 1983 Sweden developed an energy performance standard that limited the space heating 50-60kWh/m².yr (the theoretical performance of the 2006 UK building regulations). In Germany it was recognised that the average German home uses 200kWh/m².yr for space heating and that if Swedish energy standards were to be adopted then a factor four reduction in energy demand could be achieved; this led to the rise of the largely unofficial voluntary 'low energy standard.' This eventually led to a tendency for architects and builders to make claims about having built low energy houses simply because they orientated the house in a southerly direction or applied an extra couple of centimetres of insulation. After a while newspaper articles began to crop up with statements such as 'family uses more energy in their new low-energy home than in the old heritage building they previously occupied', 'mould problems in low-energy houses', or 'low-energy houses are only for the hardiest, as they stay quite chilly in winter to save on energy.' Anyway you get the point, the buildings were not delivering the required performance and the public felt duped as they understandably began to believe that there aren't any real benefits from 'energy efficient' buildings. In this context it is not surprising that German research into building physics found that low energy buildings did not always perform as expected - eerily, as recorded by Leeds Metropolitan University, this finding is reflected in UK experiences. As noted in the quote above it was with this in mind that Dr Feist set out to understand what was going wrong.

Later, in order to overcome the failures in quality assurance, RAL 965 was developed for the low energy buildings. This simultaneously created a definition for low energy buildings, protected the design standard from abuse and, as a basic term and condition for delivery and sale, provided the people requiring low energy buildings with a quality assured product. Interestingly, the most recent version of RAL 965, issued in 2009, also includes the Passivhaus standard and requires that both Low Energy buildings and Passivhaus buildings are designed using Passivhaus Planning Package (PHPP). In many respects the energy performance standards delivered by the CarbonLite Programme, which was developed by the AECB, seek to establish a programme that is akin to the RAL standard, both in terms of its numerical prescription and the development of trained and informed builders and designers.

Delivering quality assured buildings

After the successful completion, and perhaps more critically, the validation of the original Passivhaus project in Darmstadt (1991-93) Dr Feist and his team at the Passivhaus Institute began to develop the PHPP. This design tool is a simplified means of ensuring that all the requisite aspects of the comfort criteria and building physics are addressed in the appropriate manner and in the necessary detail. Whilst detailed discussion of these criteria is beyond the scope of this article, suffice to say that PHPP carefully considers heat losses and gains associated with airtightness, ventilation, thermal bridging, solar gains, internal gains and the like.

For a Passivhaus the use of PHPP is the most fundamental aspect of the quality assurance process. One of the principal benefits that PHPP offers is that the designer does not have to return to first principles as a number of assumptions have been researched, established and validated by PHI and then included in the design tool. In addition, not only does the tool include all the necessary aspects of building physics that need to be considered, but it also establishes a datum that allows one Passivhaus to be compared to another. In this respect it should be recognised that PHPP establishes a number of conventions which can simplify the design process and enable validation. At this time not all of the conventions in PHPP agree with UK methodologies, often for good reason. The heating energy demand, as calculated by PHPP, has been validated against the monitored heating energy consumption of more than 500 new homes.

Gerit Horn, in a paper on the legal aspects of designing and constructing Passivhaus buildings, remarked that the 'agreement to plan and construct a Passivhaus means that the calculation methods used in PHPP apply for the determination of compliance with the Passivhaus standard.' On this basis the requirement for a Passivhaus should form a part of the contractual obligations of the design team and the contractor, furthermore, these requirements should be clearly defined as otherwise the client will not be able to demand compensation based upon the PHPP calculations.

Recent claims in the UK

Recently I have found that I have had the issue of quality assurance in mind when I read the various articles in the press where people (journalists, clients, architects or builders) have made claims about schemes that have been designed to the Passivhaus standard or having completed Passivhaus buildings.

At first I always find the reports of a new Passivhaus very encouraging but after a while, as I read the article, I repeatedly find tell tale signs - errors and omissions - that suggest that the projects are not actually Passivhaus buildings at all, Worst of all in some cases there are even claims of building in accordance with Passivhaus 'principles' - these projects are certainly not Passivhaus buildings. Whilst they are no doubt designed and built by well meaning individuals, the projects have not been subjected to the same level of rigorous analysis (leading to inappropriate specifications), they have not used the correct design tools (leading to erroneous assumptions) and they have not been subject to the same standard of quality assurance (which means that errors can creep in and as a consequence theory and reality will not converge).

Now I can hear you, the reader, say "Do such claims matter?" To me the obvious answer is a resounding 'yes'. For instance, imagine if someone claimed to have a 'BREEAM Outstanding' office. Would you expect them to have certification to prove it, or would you think it OK for them just to pass it off without actual substantiation - just because they tried harder than usual? At the moment what I have witnessed is that this kind of thing is happening with the Passivhaus standard - here and there people are making ill-informed, often unsubstantiated, and false claims. Whilst energy efficiency is the focus of the Passivhaus standard it is an over simplification to suggest that it is 'simply' an energy standard. It is in this respect that it should be recognised that Passivhaus is also a quality assurance standard. In order to deliver buildings that perform as predicted, as a quality assurance system, Passivhaus works on a number of levels and includes; certifiers, designers, components and ultimately buildings.

Is all this quality assurance required? Perhaps it is worth considering the need for quality assurance in the context of building performance. There is mounting evidence to suggest that buildings that are being designed to achieve thermal performance standards, including the Building Regulations, are in some cases consuming in excess of 70- 100% more energy than the predicted values. In light of the recent discussions at Copenhagen, if there was ever a need for quality assured construction it is now. The old adage 'you cannot manage what you cannot measure', would seem particularly true here.

Certification schemes such as BREEAM and the Code for Sustainable Homes (CSH) are well meaning. However, by being broad-brush design tools they do not focus sufficient attention upon the key details that can influence a building's design and ultimately its energy performance aspects. By not focusing attention on the important details it is unlikely to perform appropriately when the building is realised - leading to increased energy costs, increased carbon emissions and greater occupant discomfort. In this respect BREEAM and the CSH fail to offer a sufficiently rigorous quality assurance and, furthermore, this kind of tool has been shown to incorporate what can only be described as perverse incentives that can actually encourage designs that run counter to the greater ambition.

It was in this context that, within the UK, the AECB launched its CarbonLite Programme as a means of improving the quality of the buildings that are constructed. The programme has, to date, concentrated upon improving the quality of design skills, and though practical training for builders is yet to be commenced, much of the current course could be beneficial to contractors and sub contractors as it would serve to raise awareness of key issues.

Evolution or revolution?

The rise of the CSH has led to a dearth of 'innovators' each with their own untried and untested super product/ concept. Whilst it is great that the UK construction industry is finally thinking, there is an inherent danger of reinventing the wheel at great expense. Perhaps we could in fact be learning from projects that have already been developed, trailed, tested, verified and proven to work.

The Darmstadt Passivhaus was a research project funded by one of the state governments. The building physics models for the project were complex and dynamic; much beyond what is required, affordable and replicable for normal construction. The physics was then tested by building a real house that was occupied by families for years, rather than weeks, and was rigorously monitored throughout this period (in fact the houses are still occupied). This is a far cry from the 'demonstration' houses at the BRE Innovation Park.

After all this complex research and analysis the Passivhaus Institute went on to develop a simplified design tool that that would enable mainstream construction to replicate the results. This tool became the Passivhaus Planning Package (PHPP). Since then the Passivhaus standard has been proven to be cost effective time and again in studies across Europe, meanwhile much of the UK construction industry is wasting time, and money, trying to corner a market and score a bit of brand recognition. I just find myself asking whether it would it be wiser to learn from experience. When given the choice of evolution or revolution, I'd choose evolution.

Why are such issues of building physics and quality assurance vital? In light of the threat of climate change the government has undertaken a legally binding commitment to reduce the UK's carbon emissions by 80% by 2050 and other issues deserving attention, such as fossil fuel depletion and fuel security, there is a significant challenge to the status quo. This reduction target is not theoretical, to address climate change no amount of accountancy will solve the problem, this target must be achieved in reality.

It is in this context that the research by Leeds Metropolitan University becomes so powerful for they have found repeatedly that homes can, and are, failing to perform in accordance with design standards. As the theoretical targets become more stringent so the gap appears to widen. It is worth recognising the systematic errors that can occur in low energy or 'super-insulated' buildings designed to something akin to PassivHaus 'principles':

• the appropriate building physics design model is not used from the beginning of the design process, ie. not using PHPP - this leads to systematic errors

• the correct area and geometric conventions are not used to establish the energy performance - heat losses and energy consumption figures can be distorted

• incorrectly calculated U-values lead to an under estimation of the heat losses (an error of 30% is possible)

• the notional Passivhaus U-values are used - leading to an increase in energy demand (using this method it is unlikely that the 1 5kWh/m2.yr target will be achieved)

• thermal bridging is not accounted for appropriately which can lead to increased heat losses. (Poorly defined and inadequately designed details can result in 50-100% more heat loss than intended)

• incorrectly specified windows and doors can lead to heat losses being 60% higher than expected due to additional heat losses via the frame and spacer bar

• incorrectly specified heat recovery ventilation systems can lead to an increase in energy consumption of 25% (specifically by the use of uncertified heat recovery systems without due consideration for impact upon efficiency of the system as a whole - this will be discussed in more detail in part two of this article.)

• pressure tests are not conducted, ie. actual performance cannot be verified. The resulting error can mean that infiltration heat losses are >300% higher than required

• it can be concluded that no space heating is required which leads to ludicrous claims of affordable 'zero heating' and 'going beyond Passivhaus' (there is not space here to discuss this matter in detail, but suffice to say that it was the recognition that the reality of 'zero heating' was in fact impractical that lead to the Passivhaus standard being structured as it is. This matter was also explored in AECB/CarbonLite report 'A Comparison of The Passivhaus Planning Package (PHPP) and SAP.)

• poor construction details (failure to design for construction and inability to design out defects that will impair thermal performance - thermal bridging, poor airtightness, thermal bypass etc)

• poor site quality assurance - poor airtightness, gaps in insulation leading to constructed thermal bridges, thermal bypass etc. Instances of poor workmanship are inexcusable for the simple fact that the skills that are required are, in their own right, not complex. All we are talking about is attention to detail which was once customary practice and takes no more time than a more sloppy approach.

These failings, many of which also are commonplace within the construction industry, have a number of impacts, including the fact that the owners and occupiers of modern buildings are not reaping the full benefits of reduced fuel bills and improved thermal comfort. It also means that theoretical carbon emissions are not actually being achieved and as a consequence will not deliver the government's legal obligations. In this context it is notable to consider that where a building fails to satisfy the legal and/or contractual obligations mandated by performance standards, ie. Passivhaus or Building Regulations, designers and constructors may be exposed to claims of professional negligence.


Returning to Dr Feist's quote it can be seen that the goal of the Passivhaus standard is not simply to 'design to a number'. It is much more than that. The ambition of the standard is to close the gap between design and practice; to have theory and reality converge. If the UK is to achieve an 80% reduction in carbon emissions by 2050 the quality of the buildings that it builds, and refurbishes, needs to be vastly improved. This may be achieved by Introducing the appropriate quality assurance systems throughout the design and delivery process. Buildings without the rigorous quality assurance are far less likely to succeed in their aims and ambitions, particularly in very low carbon/energy buildings. It is in this context that the purpose of this article was to shed some light on the subject of the Passivhaus standard and the quality assurance that is associated with delivering such buildings at a national level and on individual building projects.

Accessed online: 7th August 2014

CREST Centre - South West College - Passivhaus Certified, BREEAM excellent and Zero Carbon


Paul McAlister Architects were delighted to win an open tender for the provision of architect led design team services for the provision of the new CREST Centre for South West College Enniskillen. This project is one of the most sustainable projects in Ireland and will be the first commercial building in Northern Ireland that will achieve the Passive House Certification. The project is distinguished as it will achieve all of the following three sustainable credentials:

  1. Passivhaus Certified for Energy efficient envelope and ventilation system
  2. BREEAM excellent in terms of the BRE sustainable benchmark for UK commercials buildings
  3. The building will also be Zero Carbon, this means that the building can provide, by renewable energy, it own source of heat and lighting.

Whilst a combination of these sustainable criteria has been attempted in other parts of the UK, this will be the first example in Northern Ireland or Ireland and will become a benchmark building for sustainability.

South West College is one of six Further and Higher Education Colleges in Northern Ireland and was formed as a result of the merger of the former Colleges of Fermanagh, Omagh and East Tyrone on 1 August 2007.  South West College services the geographical area of Counties Tyrone and Fermanagh.  There are five campus locations at Cookstown, Dungannon, Omagh, two at Enniskillen (main campus and Technology and Skills Centre) and a number of out centres.  The College has approximately 500 full-time staff and a similar number of part-time staff and an annual budget of £39M. The college offers a wide range of vocational and non-vocational courses, training courses such as Training for Success, Steps to Work and provides a service to the community, local schools, business and industry.  It provides courses ranging from basic skills to Higher National Diploma and Degree Level programmes.

The CREST centre will provide industry Research & Development, demonstration and testing facilities for new renewable energy products and sustainable technologies. The facilities will be used by small companies within the region who have ideas for new products but who currently do not have the physical and/or technical capacity to develop, test and commercialise these. Within CREST facilities and staff will be accessible to develop, demonstrate and test new technologies and show how these can be integrated practically and sensibly to achieve energy savings. The CREST centre will form one component of a wider bid for European funding to support Research & Development in renewable energy and smart technologies within small businesses in the border regions of Northern Ireland, Ireland and western Scotland.

The CREST centre will comprise of three areas; the Pavilion, Research & Development Lab and Hub. The Pavilion will be newly developed and the Hub and Research & Development lab will be integrated into the existing Skills Centre building.

The Hub will form the central office area within the CREST centre and will comprise modern office and meeting space where the CREST team will meet with companies to discuss their requirements and outline the services available. Within the reception area of the Hub, real time visual data monitoring screens will be located. These will display easy-to-understand graphs and tables to analyse the energy performance of a variety of renewable energy installations (e.g. wind turbines, solar panels) located within the region and provide useful data such as information on CO2 savings and energy output. The CREST centre in Enniskillen will form the core of a larger network of satellite facilities in Sligo, Cavan and Dumfries in Scotland, and modern electronic communication facilities will be required within the Hub to link with these sites (e.g. Videoconferencing, web conferencing etc). The hub will be accommodated in the existing building which will require adaptation. Within the Research & Development lab a range of advanced prototyping, testing and development facilities will be available to enable staff at the centre to support companies with practical hands-on new product development. The Research & Development lab will comprise a large workshop facility which can be divided into smaller project workspaces. It is envisaged that some of the CREST projects will involve the development of highly innovative ideas for which IP protection will be required and thus some of the project workspaces will need to be screened from public access to prevent disclosure issues. Equipment within the Research & Development lab will include a laboratory scale wind turbine, biomass heating apparatus, heat exchangers, heat pumps, solar heating and photovoltaic and various monitoring, testing and ancillary equipment. This lab facility is to be accommodated within existing accommodation which will require adaptation. The Pavilion area of the CREST centre will provide demonstration and testing facilities to showcase innovative products and processes and the use of renewable technologies in construction. The Pavilion will be designed to engage industry through experiencing (seeing, touching) new sustainable technologies and materials allowing for a deeper engagement in and understanding of the techniques on display. Products and processes will include new construction technologies – building materials e.g. hempcrete, insulation etc. and renewable energy applications e.g. heat pumps, solar panels. It is planned that the Pavilion will be a dynamic facility which will allow for annual/biannual reconfiguration to include emerging technologies.


Low Energy Timber Windows and Glazing

Timber window manufacturers have focused hard on their products and have been rethinking, redesigning and reconsidering. Consumers might be forgiven for thinking twice before choosing timber windows. They certainly earned themselves a bad reputation in the sixties and seventies and this reputation for poor quality in workmanship and material opened the door for, first aluminium windows and then later, uPVC. Thankfully, the quality of timber windows has increased greatly but dispelling the perception that timber windows need intensive maintenance regimes that could carry hidden costs is not so easy to fix. Lately, not just the materials and workmanship have changed, the industry has learned from its rivals and introduced modern production and finishing techniques, including offsite pre-finish­ing and quality assurance schemes.

From an environmental perspective, drivers such as the Environmental Protection (Prescribed Processes and Substances) Regulations of 1991, have led to a shift by the industry to using 'safer', preservative treat­ments and coatings, with some going even further and producing 'eco' windows specifically for this sector of the market. Manufacturers have also paid heed to performance expecta­tions, adopting an 'holistic' approach to the specification of all materials used, and giving due attention to better component design.

Now, window manufacturers build into the design a very wide range of factors. For instance, which timber species should be used, chosen on the basis of its durability, dimensional stability and above all its sustainability and environmental impact, with many now offering Forest Stewardship Council or Pan European Forestry Council certification as standard across their range. Certainly, at the 'green building' end of the timber window spectrum there have been some great advances in the UK with at least two new facilities starting production of high quality, high environmental standard and super efficient ranges.

The wood coatings' sector has also responded to environmental concerns (and legislation changes of course) by reducing solvent content and developing high-solids' coatings and improved water-borne formulations, with lower dirt retention characteristics. However, the expectation of higher performance and sustainability carries with it its own demands. Pre-finishing of external joinery has many advantages which offer the end user a very high quality product. But in order for the end user to benefit from that quality, there needs to be a parallel responsibility by the whole construction industry (the builder in particular) to handle and use this pre-finished joinery in a manner which reflects its value.

There are ways of ensuring that the products (windows and doors) are given adequate protection until the point of hand-over. This may require the adoption of such practices as installing windows into openings built around pre-fabricated formers. One of the most recent developments in the industry has been the introduction of energy performance certification, similar to that given to domestic appliances (see below).

It is clear that the joinery and wood coating industries are responding positively to change through a process of integration and closer co-operation. It is only by further extending this approach, working with the installers, going beyond the manufacturing operation into the building process, and above all, meeting and addressing the requirements and concerns of the consumer, that timber windows will secure their rightful place back on our buildings.

Passivhaus windows

A development for the UK has been the introduction of windows manufactured to the German Passivhaus standard. Not only do these incorporate the most advanced triple glazing, with typical glazing U-values of around 0.6W jm2K, but to meet the stringent comfort criteria of the Passivhaus standard, solid timber frames are not sufficient. As a result various innovations incorporating thermal breaks in the timber frames have been devel­oped. A number of ranges are now available in the UK, mostly manufactured in Europe,

and some certified by the Passivhaus Institute as complying with its requirements. Arguably these represent the limit of thermal performance available with currently available glazing and frame technologies. They will be required for those designing to the Passivhaus standard, as well as offering solutions for those working to higher levels of the Code for Sustainable Homes.

Turning to glazing, on new homes, double glazing is just about standard now but many existing properties still need to be upgraded. With our increasing love of large glazed areas, it may well pay to consider enhanced double glazing, or even triple glazing, if we want to keep those wide open views but avoid large heating bills, and minimise carbon emissions. Whilst double-glazing can reduce heat loss through windows by up to 50%, our love of large glazed areas is undermining these reductions. The technology for high and ultra-high performance glazing is well established, and the uptake is improving all the time but until newer advanced technologies, like vacuum glazing, become commercially viable, which is likely to be some years yet (see Volume 2 for a description), there is not huge scope for improvement on the current best practice.

An air gap between the glass of 16mm and 20mm is considered to be the optimum, and the difference between the two is negligible. Below 16mm the direct heat transference between the panes reduces the effectiveness and over 20mm air convection between the panes that has a similar effect. The basic standard for sealed unit double glazing, as required by the Building Regulations, would be a 28mm thick unit combination as such: standard float glass / 20mm air gap / hard coat Low E. This would have a U-value typically of about 1.8Wjm2K.

Low-e coatings

Low-e (Iow emissivity) coatings are a micro­scopically thin metal oxide or semiconductor film applied on one or more surfaces of the glass, usually on a face between the panes of a double glazed or triple glazed unit. Double glazing, using low-e coated glass, gives energy conservation properties equivalent to standard triple glazing. The coating is usually applied on the outer face of the inside pane (or outer face of both inner panes in triple glazing), facing the air cavity. These coatings work by reflecting long wavelength heat generated within the room (radiators and heating appliances), back into the building, whilst at the same time allowing short wavelength, solar energy (from daylight and sunshine) into the room. The incoming short wavelength solar energy is re-radiated by internal building surfaces at longer wavelengths, which are then re-reflected by the coating back into the room.

Low-e coated glass looks identical to ordinary clear glass, as the coating is almost invisible. Its effect on light transmission and reflection is hardly noticeable. It can be used everywhere, from the largest office block application to domestic conservatories, windows and doors and whilst designed for double glazing, it can also be used as the inner pane in secondary glazing, although hard coat low-e would be recommended for this application as it is tougher and more resistant to scratches. The advantages include the following;

  • improved insulation
  • reduced heating bills
  • reduced carbon dioxide emissions
  • reduced condensation
  • reduced cold spots and down draughts
  • takes advantage of the sun's heat

Gas fills and glazing bars

Aragon and other gases

Instead of air; argon, krypton or xenon gas can be injected between the panes. These gasses have better insulation properties than air and contribute to much better overall insulation. For instance, with an argon fill the U-value would be reduced by over 30%. The gasses only displace a proportion of the air in the unit and it is generally accepted that the double glazed unit should achieve a 90% fill gas-to-air concentration. This concentration will gradually reduce with age, at a rate estimated from 0.5 to 1 % per year. Units filled with argon do not degrade significantly until they reach 75% concentration, which adds up to about a 20 year performance durability, after which the unit will perform the same as an air filled unit (this may vary depending on the type of spacer bar used).

Not all double glazing manufacturers are yet able to offer double glazing with a gas filling. Contact the GGF1 for details of those that can. Other gasses, such as krypton and xenon, can be used but they are harder to source and more costly. Chris Herring, of the Green Building Store- who sell a range of exception­ally high specification windows said "Given optimal cavities, argon filled units give virtu­ally the same performance as those filled with the denser and much more expensive gases Krypton and Xenon. Their advantage is that they enable the cavity of the glazing unit to be reduced without affecting performance. Given the expense, their use is best limited to retrofit units which are required to fit narrow glazing situations. High performance argon filled triple glazed units, for example 4-18-4-18-4 with two soft coat low E coatings can achieve almost 0.5 W/m2K centre pane value".

Spacer bars

Advanced technology spacer bars are now becoming an essential part of any double glazed unit that intends to achieve seriously low U-values. There are now a number of different types available with the foam rubber 'Superspacer' from Edgetech IG3 being the most common. Herring said "I am not convinced there is much to choose between the advanced spacer bars, they all seem to perform well, with pretty marginal differences. The important thing is to get away from metallic spacers to true warm edge spacers. Our Ecoplus range of windows use the Superspacer, which we have found to be perhaps the spacer with the widest take-up in the UK. However our Ecoclad range normally use Swisspacer or Thermix4, which are more widely available in Eastern Europe where they are manufactured."

Whichever of these advanced spacer bars you choose it will significantly reduce the heat loss around the edges of the units. Most people will have witnessed the condensation that forms around the edges of double glazed units, well the advanced spacers significantly reduce or eliminate this (condensation on glazing may vary with a number of environmental factors as well as technical factors to do with the composi­tion of the unit). However, the most significant savings using these types of spacer bar will be achieved on windows where small (Georgian) type glazing units are used due to the edge to area ratio. However, their use on all sizes of double glazing units will enhance the energy saving potential of the window. Warm edge spacers can also reduce sound too - up to 2 decibels (according to Edgetech) compared to aluminium spacer bars.

Comparing low-e glazing

Hard coat - also known as pyrolytic coating, this coating is applied at high temperatures and is sprayed onto the glass surface during the float glass process.


  • the coating is durable, which allows for ease of handling and tempering
  • can be tempered after coating application
  • can be used in single glazing applications
  • utilizes passive solar heat gain.


  • higher U-values, compared to soft coat, low-e, products
  • higher solar heat gain coefficient, compared to soft coat, low-e, products
  • hard coat glass also has the possibility of a slight haze, which can be visible at certain angles.


K glass is made by Pilkington.6

NOTE: Pilkington do supply a type of soft coat low E glass known as Optitherm but in the UK most of their Low-E supply is in the form of Pilkington K Glass.

Soft coat - also known as ‘sputter coating’, this is applied in multiple layers of optically transparent silver, sandwiched between layers of metal oxide in a vacuum chamber. This process provides the highest level of performance and a nearly invisible coating.


  • high visible light transmission with optical clarity - minimal color haze
  • ultra-low emissivities, giving optimum winter U­values
  • up to 70% less UV transmission, compared with standard clear glazing.


  • soft coat low-e must be used in a double glazed unit; the soft coating is sensitive to handling
  • most soft coat, low-e, products require tempering the glass prior to the coating application
  • edge removal of the coating is required to ensure a proper seal in an insulated unit
  • more expensive than hard coat, low-e, glass.


Saint-Gobain (Planitherm Total)5

Pilkington (Optitherrn)6

Interpane (Iplus)7

Upgrading Windows - As Easy as A, B, C!

Poorly insulated window frames and single glazed windows account for up to 20% of heat loss in the average home. If you upgrade to energy efficient windows, you can help reduce your energy consumption and save money!

In recent years, windows have undergone a technological revolution to bring them up to today's insulating standards. Upgrading single glazed windows with energy efficient ones will not only make the property more secure, warmer and more comfortable to live in, but they will also help reduce your home's energy bills and enhance your property's overall appearance. The wide variety of materials, sizes, and colours for windows has opened a new world of design possibilities, which is limited only by your imagination and budget!

Above: Passive House standards can now be achieved with these Upvc/Alu-clad windows from Internorm (Passion Vetro Design and Thermoj). They are triple glazed as standard and come in a range of shapes and colours. Visit www.ecoglaze.iefor more information.

So what are energy efficient windows?

They are windows that help contain and conserve heat with i n the home, resist condensation and benefit from solar gain. They can be made using any frame material aluminium, uPVC or timber or even a combination of materials. Energy efficient windows are easy to recognise - simply look­ for its energy rating, as classified by the British Fenestration Rating Council (BFRC), where 'A' is the most efficient. The BFRC scheme assesses the total energy performance of a complete window (not just the glass) and allows accurate comparison of the performance of windows under identical conditions. The most energy efficient windows (A being the most efficient) also carry the Energy Saving Recommended logo issued by the Energy Saving Trust. NB. Glass doors are to be included in the BFRC rating scheme in 2009. Conservatories are currently excluded.

How much do energy efficient windows cost?

The cost varies not only between the various ratings but is also dependent on the frame materials, type of glazing used and the size and style of the overall window. A-rated windows will cost more than B, C, 0 and E rated windows, but when offset against the energy savings you will make, this is comparatively low.

How much would I save on my energy bills?

According to the Energy Saving Trust, when you replace single glazed windows with Energy Saving Recommended double glazing, you can cut heat lost through windows by half, as well as saving around £140/€160 a year on your heating bills (which at the time of writing this, was the equivalent of around 400 litres of home heating oil!) It can also save you around 720kg of carbon dioxide (CO2) a year.

How much could I reduce my carbon footprint by?

It is generally recognised that if you live in a single glazed house and install energy efficient windows you could reduce the energy you use by 0.30 tonnes (or 18%) per year. This calculation is based on 'an average, semi-detached house'.

Frame Type

The material used to manufacture a frame not only governs the physical characteristics of the window, such as thickness, weight, and durability, but it also has a major impact on its thermal characteristics. Since the frame represents 10-30% of the total area of the window unit, the frame properties will definitely influence energy performance and looks.

uPVC - A derivative of plastic, this material requires no painting. The choice of colours and textures has grown, from imitation timber to stand alone colours. They can easily be cleaned and aren't subject to attack from woodworm and insects. However, they can warp or discolour over time.

Timber Wood - this is a natural and sustainable material which comes in a variety of colours depending on the type of timber being used. It's warm to touch and can be stained or painted to suit your interior style. Minor maintenance is required to prevent moisture building up and rotting the frame.

Aluminium - This is perhaps the strongest and most durable of materials as it maintains temperature in accordance with the seasons and has an excellent lifespan. However, when it's freezing outside, aluminium can be exceptionally cold to the touch, which is why some window manufacturers have introduced Alu-Clad systems which have aluminium outside and another material inside. The aluminium protects against rain, hail, UV light, dust and air pollution, and comes in a range of colours or even timber effect finishes. On the inside, timber, vinyl or uPVC can be used to provide a warmer and decorative finish.

Above: These vertical sliding sash windows combine the elegance of traditional sash windows with all the benefits of modern uPVC - strong, won't rot, warp or require repainting. Available in cream, white or oak with brass, chrome or white window furniture. BFRC rated 'C and available from Camden Group,


There are three fundamental approaches to improving the energy performance of glazing products (two or more of these approaches may be combined).

1. Alter the glazing material by changing its chemical composition or physical characteristics, ego tinted glazing.

2. Apply a coating to the glazing surface.

Reflective coatings and films were developed to reduce heat gain and glare, while low-E coatings improve both heating and cooling performance. There are even coatings available for the exterior to break down dirt!

3. Add multiple layers of glazing with low conductance gas to the spaces between the layers; and use thermally improved edge spacers between the panes.­

Upgrading your glazing to include specialist coatings will help you save money controlling solar gain.

Understanding the Jargon ...

Double Glazed - Two panes of glazing with air spaces in between.

Triple Glazed - Three panes of glazing with air spaces between each.

Low-E (emittance) Coating - The coating is a microscopically thin, virtually invisible, metal or metaIIic oxide layer deposited on the inside of glazing primarily to reduce its Uvalue. The effect is reduced heat loss and better solar gain.­

Argon &. Krypton Gas - Originally, the space between panes was filled with air or flushed with dry nitrogen just prior to sealing. However, if the space is filled with a less conductive or slow-moving gas like Argon or Krypton, it minimises the convection currents within the space and the overall transfer of heat between the inside and outside is reduced. Argon is inexpensive, nontoxic, nonreactive, clear, and odourless, while Krypton has a higher thermal performance but more expensive to produce.

Tinted/Obscured Glass - Tinted glass is usefuI in controlling glare but solar heat gain and visible light transmission may be reduced, which is a benefit in summer but not in winter. The tint has no effect on the U-value. Obscured glass is used to protect privacy, but it can also reduce solar light.

Spacers - Higher quaIity spacers between panes can reduce 'fogging' and condensation, while some can incorporate a thermal/warm-edge for better insulation. This is particularly effective if you have aluminium or uPVC frames.

Safety Glass - Glass can be toughened (via repetitive heating and cooling processes) or laminated, both of which are difficult to break and ensure injury is reduced if they are. Laminated glass is a sandwich of two layers of glass with a plastic sheet 'filling'.

Top Tips

  • Windows and roof lights should be positioned where they will maximise solar gain.
  • The minimum standard for an 'energy-efficient' house is Low E, Argon filled cavity double glazing.
  • Ensure draught proofing seals and spacer bars on windows are working effectively - move a candle along the edge to see if it flickers. This may indicate air is leaking
  • Replacement windows & doors must comply with current building legislation on thermal performance, fire safety and ventilation. Ask your supplier to certify this before installation.
  • Decorate & Improve Your Home.

Operating System

When you select a window, there are numerous operating profiles to consider. Traditional profiles include projected or hinged types like casement and French windows; or sliding types like double/singlehung and sash windows. In addition, the current window market includes storm windows, sliding/folding and swinging glass doors, skylights and roof-mounted windows, and window systems that can be added to a house to create a bay or bow. The choice is vast' Modern profiles may also offer additional benefits of 'tilt-in' or 'tilt and turn', which make cleaning exterior panes possible from inside the house.­

Heat loss is a major concern for today's home owners and one of the key reasons we opt for multiple glazed units with gas infill. However, if your period property has traditional timber sash or casement windows, you won't want to replace them. Frank Clissmann from says the best way to make traditional timber sash windows more energy efficient is to draught proof the frame. He adds, "replacing single glazing with double glazing can reduce a room's heat loss by around 6%. However research from Glasgow Caledonian University found draught proofing an old sash window can reduce heat loss by around 86% without replacing the single glazing. This method is also more environmentally friendly because there is no waste."

 Other Considerations

  • Acoustic Performance - Noise is an environmental problem and makes life very difficult for some people. One way to reduce noise in your home is to use thicker glass or more of it and improve the seals around the window.
  • Security Performance - Window locks and thicker glass or multiple panes can improve safety.
  • Warranty – Lifespan and installation warranty will vary between manufacturers.

Did You Know...?

  • Trickle vents on windows will provide sufficient ventilation to reduce the build up of condensation and odours, and also control heat loss in your home. Shutters and thermal blinds or lined curtains and can help minimise heat loss at night.
  • Replacing single glazed windows with energy efficient windows can help increase the resale value of your property.
  • Shutters and thermal blinds or lined curtains can help minimise heat loss at night.

Changes to Part G Building Regulations

Will the updates to Part G of the Building Regulations result in water efficiency and safer hot water systems in new dwellings as promised by the previous government? In this article Cath Hassell covers the updates that are most relevant to sustainable building.

The updated Part G finally came into force on April 6th 2010. Originally planned for April 2006, it was shelved by Yvette Cooper, the then Housing Minister ¹. We were then promised its arrival in October 2009, only for it to fall foul of a European regulation. But it is here now and, unless work has already started on site, or planning permission has been granted, and work commences before April 2001, then any building work must conform to it.

The document has increased from 14 to 43 pages and now has six sections compared to three previously. The three headline changes to Part G are:

  1. a requirement to limit hot water at bath taps to 48°C,
  2. enhanced safety for all stored hot water systems, and; the requirement for all new dwellings to achieve a water efficiency standard of 125 litres use of wholesome water per person per day.

There are other updates that stand out.

  1.  Rainwater or greywater can be used in buildings for certain purposes;
  2. compost toilets are referred to for the first time;
  3. solar thermal systems require automatic protection against legionella; and hot taps must be positioned on the left of any appliance.

Rainwater and greywater

G1 allows for the provision of water of suitable quality to any sanitary convenience fitted with a flushing device, whilst requiring a supply of wholesome water- to showers, baths, bidets, washbasins, sinks (in an area where food is prepared), and any place where drinking water is drawn off. The document classifies alternatives to wholesome water as: water from wells, springs, boreholes or water courses; harvested rainwater; reclaimed greywater; and reclaimed industrial process water.

Rainwater and greywater can be used for WC and urinal flushing, washing machines and irrigation, provided an appropriate risk assessment has been carried out. The risk assessment should ensure that any rainwater or greywater system does not cause waste, misuse, undue consumption or contamination of wholesome water.

Enhanced provisions on hot water supply and safety

Under the old Part G, there was a stated requirement for safety measures to ensure the safe operation of unvented hot water systems greater than 15 litres. Part G3 has now been extended to cover all types of hot water system including thermal stores and vented cylinders. In brief, any hot water system, including the associated storage and expansion vessel, must be designed to cope with the effects of any temperature or pressure changes that occur in normal use, or as a consequence of an operating fault. If the operating temperature of the stored hot water could exceed 80°C under normal operating conditions (potentially thermal stores, and hot water cylinders connected to solar panels or solid fuel boilers), a temperature mixing valve (TMV) must be installed on the hot water draw off to limit the temperature to 600C ³. Ensuring that hot taps are always installed on the left hand side has long been good practice so that blind and partially sited people know which is the hot tap; it is good that it is finally a legal requirement. Controls to provide automatic protection against legionella proliferation in solar thermal systems are now required. These controls ensure that either the back up boiler, or the immersion heater, raises the temperature of the solar heated stored water to 65°C for 1 hour a week to ensure that there is no risk of legionella in poorly designed systems.

Prevention against scalding

Part G3 also states that the hot water supply temperature to a bath should be limited to a maximum of 48°C. To comply, a TMV (or similar) which will fail-safe at temperatures higher than 48°C, and cannot be easily altered by the building users, must be specified. A TMV installed on the hot water draw-off, where it could be easily accessed for the required yearly maintenance, would be the optimum solution. However, because of concern about the potential, for colonisation of waterborne pathogens (mainly legionella) in the pipe runs, the length of supply pipe between the valve and the final outlet is required to be kept to a minimum ⁴. In effect this means a TMV will be sited under the bath in most situations. Due to the concern within housing associations of increased maintenance costs, coupled with the length of time it has taken Part G to come into force, the market has already provided solutions to this regulation. There are mixer taps available on the market with an integral TMV in the tap body, making maintenance far easier. Private developers are still likely to install TMVs under the bath so that they have as wide a choice of bath taps as possible; any future maintenance will be the responsibility of the householder.

Compost toilets

G4 states that compost toilets require a suitable arrangement for the disposal of the waste either on or off the site, and that the waste must be able to be removed without carrying it through any living space or food preparation area. It further states that composting toilets should not be connected to an energy source other than for purposes of ventilation or sustaining the composting process. This effectively rules out the installation of dehydrating composting toilets, which must be applauded. To use an electrical element to dry out faeces (3.5-4 kWh every 24 hours) makes no environmental sense at all, and is something I have been arguing against since 1998. You can still install compact composting toilets if space is limited and there is no reliable water supply to the building''.

Water efficiency and Regulation 17K

For the first time ever the Building Regulations will address water efficiency. There is a maximum allowable amount of 125 litres of wholesome water per person per day in dwellings ⁶. This is known as Regulation 17K and at face value looks good given that average UK use is 150 litres/ person/day, and therefore this regulation requires an approximate 18% reduction in water consumption. To show compliance there is a calculator available online, which is straightforward to use ⁷. WCs, baths and taps need to be chosen and the flushing volume, or flow rates of all the appliances must be entered. The calculator provides a total water consumption figure in litres/person/day, which is then presented to Building Control to show compliance. It seems straightforward but this is where the problem lies.

The water calculator that is used to determine whether a dwelling will reach the presumed use of 125 litres per person per day, is the same calculator that is also used to show compliance with the Code for Sustainable Homes. Although the original calculator was upgraded in 2009, it is still subject to many of the same problems that beset the original, not least the seemingly random uses of water it assumes (right down to 2 decimal places in some cases). In some aspects the new calculator is even worse; the most notable example being the 'normalisation factor' that knocks almost 10% off the calculated usage to arrive at a reduced daily consumption.

The calculator assumes a person spends 5.6 minutes in the shower, fills the bath halfway up before getting in (50% of maximum volume), and flushes the toilet 4.42 times a day ⁸. If they have a bath and a shower in the dwelling they use the shower 80% of the time and the bath 20% of the time ⁹. The calculations used to determine consumption from taps is unclear. Current calculated usage ranges between 11.24 to 13.00 litres at kitchen sinks at flow rates as varied as 2 - 6 litres and between 4.74 to 11 .06 litres usage for flow rates between 2 - 6 Iitres at the wash basin. It is assumed that the property will have connections for a washing machine and dishwasher, and if no appliances are specified a default figure is used of 17.16 litres per person for a washing machine, and 4.5 litres per person for a dishwasher. If a waste disposal unit is specified, the calculator assumes a water use of 3.08 litres per person. Inefficient water softeners (using more than 4% for replenishment) will add to the load. Water softeners that use less than this amount for replenishment can add 4.4 litres to daily use, yet the calculator assumes zero water consumption.

The calculator produces a 'total calculated use' figure in litres, multiplies it by a 'normalisation' factor of 0.91 to arrive at a 'total water consumption' in litres/person/day. It then adds 5 litres for outside use, to say whether the dwelling meets Regulation 17K. 1 24.9 litres meets the regulation, 125.1 litres doesn't. The calculator adds 5 litres for external water use regardless of the actual situation. Living in a flat with no outside space? You use 5 litres of water per day. Living in a large detached house with a swimming pool, jacuzzi and an automatic irrigation system? You use 5 litres of water per day. Now, there are different arguments put forward about outside use only happening part of the year, or that once a swimming pool is filled up it requires little water to refill. But adding on 5 Iitres for all dwelling types just makes the calculator look stupid. Incidentally, a swimming pool that is just 8m by 4m x 1.5 m deep, installed in a dwelling occupied by a family of four would use up 6.6 years worth of outside use for each resident at 5 litres per day, a usage of water that shouldn't be classified as 'efficient'.

What is worse is that if you install several showers, with different flow rates you can offset high flow rate showers against low flow rate ones, thus allowing power showers in the main bathrooms. This enables large houses with several en-suite bathrooms to be fitted with showers with a flow rate of 15 litres per minute, (as long as they are offset with lower flow rates elsewhere in the dwelling), whilst that cannot happen with just one shower, as shown in Tables 1 and 2. Five minutes in a shower at 15 litres/minute uses 75 litres of hot water with a carbon intensity of near to 7kgC02 per m3. Allowing power showers in a dwelling that is supposed to be water efficient is surely nonsensical.

C02 emissions from hot water use

You can install 15 litre/minute power showers, have a swimming pool and jacuzzi and still pass the water efficiency criteria within Part G! So how much does this really matter? Isn't it the CO2 from heating and lighting our homes which produce all the CO2 emissions? Well no actually. Within new homes the CO2 emissions from water use will be as much as those for heating the property, even in a dwelling without power showers. When looking at the existing housing stock in the UK, the government has calculated CO2 emissions from hot water use as 6% of the UK's total CO2 emissions, and is concerned enough about that figure to have encouraged a number of initiatives to reduce it.

At the urging of DEFRA, the BMA (Bathroom Manufacturer's Association) has devised a water efficiency rating system that is clear, easy to understand and has been enthusiastically taken up by manufacturers. Showers with a flow rate of between 10 and 13 litres/minute are rated as poor while showers with a flow rate greater than 13 litres/minute are in the red zone. And, under the CERT scheme, energy companies are being paid to send households flow regulators that reduce flow rates from existing showers to less than 8 litres/minute. There are some good measures around to reduce hot water use in existing dwellings, to ensure that there is a greater choice of water efficient appliances on the market and that they are easy to identify. It's a shame there is no requirement to fit them in a new dwelling.


In summary, there are some good aspects about the changes to Part G. However, using the water efficiency calculator as it currently stands will do little to ensure that dwellings (especially houses as opposed to flats) built outside of the social housing sector will meet the government's stated aim of water efficient homes. It is to be hoped that the new administration will realise this and will bring in a set of proscriptive standards, such as the AECB water standard, as soon as possible. If not we will have the farcical situation where the average householder is being urged to choose a water efficient shower for their bathroom upgrade, whilst in the government's so called 'water smart' new homes, the residents will be splashing away under their power showers.


1. The official reason being that the industry had enough to get to grips with because of all the changes to Part L, which happened at the same time.

2. Wholesome water is the current term for potable water which, in this situation, refers to water supplied from the mains.

3. This TMV needs to be fitted as well as the TMV limiting bath water to 48°C.

4. If intermittent use of the bath is anticipated, provision should be made for high temperature flushing. Again this is to prevent legionella proliferation and is mostly aimed at little used baths in hospitals and nursing homes.

5. The best one I have found is the Separett which diverts urine and has an integrated fan to vent the chamber. The 12V model uses just 0.046kWh of electricity every 24 hours.

6. The figure is based on Levels 1 and 2 of the Code for Sustainable Homes, which requires an internal use of 120 Iitres, with 5 Iitres for outside use added

7. WWW.WRCPLC.CO.UK/PARTGCALCULATOR/DEFAULT.ASPX is a link to the water calculator itself. The documentation from CLG as to how the methodology works can be found at: WWW.PLANNINGPORTAL.GOV.UK/UPLOADS/DR/WATER EFFICIENCY CALCULATOR.PDF

8. Reduced from 4.8 times under the original calculator.

9. The old calculator assumed if there was a bath and a shower in the dwelling a resident would use the shower 60% of the time and the bath 40% of the time. As this meant only baths with ridiculously small volumes could be specified in dwellings built under the Code for Sustainable Homes, it was changed.