sustainable homes

Thermal Bypass - What is it?

Thermal Bypass - What is it?

The Government's legally binding objective of achieving an 80% reduction in national CO2 emissions and the drive for zero carbon homes and buildings is focusing attention upon building design and procurement.

Zero energy for all?

Zero energy for all?

From 2020 onwards all newly built or renovated houses in NI and ROI will have to comply with the Nearly Zero Energy Building (NZEB) standard. How that requirement will be put into practice remains unclear but there are some general rules we already know will have to be followed ..

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)

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.

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.


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 - 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

The 'zero carbon' definition

The definition of zero carbon has been under review and discussion since the initial proposal of the standard. The intention has always been that it would mean 100 percent reduction in net emissions relative to a dwelling compliant with the 2006 Building Regulations (England and Wales) - according to the initial definition, this was where any emissions created were offset by those 'saved' using on-site renewable capacity. Under what exact terms this will eventually be enforced and what the uplift in cost might be (and to whom) remains unresolved at this time. Carbon emissions have been separated into what are now termed ‘regulated’ and ‘unregulated’ carbon emissions. Regulated emissions are those from fixed building services, i.e. heating, ventilation and lighting; unregulated emissions are those relating to energy used by the building occupants, e.g. from cooking or electrical appliances. The initial plan was that 100 percent reduction in both would be the target - the L6 standard. Concerns about whether this was a realistic target in practice led the government in 2011 to alter the definition of zero carbon to include only the ‘regulated’ carbon emissions. This means that zero carbon can now refer to either Level 5 or Level 6 of the Code for Sustainable Homes.

Building regulations compared to CSH
Building regulations compared to CSH

The Zero Carbon Hub, a public private partnership, has been working since 2008 to support the delivery of zero-carbon homes, and this includes the development of a final definition for zero carbon. The Hub's extensive work has included publishing various advisory papers and carrying out useful consultations.

Allowable solutions

Achieving 100-percent reduction in carbon emissions, even if from regulated emissions only, involves the significant use of on-site renewable energy sources. The practicalities of having enough roof space, not to mention the cost burden, has led to a further strategy being introduced - allowing a certain proportion of the emissions reductions to derive from off-site sources or what are termed 'allowable solutions’. What exactly these will be or how they will be delivered is again unknown, but will most likely involve a payment towards the cost of introducing carbon-saving projects. The proportion in carbon reductions that will have to be achieved by the house itself is termed 'carbon compliance'. The split between these two is a matter of further debate. Initially it was thought that 70 per cent of the emissions reduction would be met by carbon compliance and 30 per cent by allowable solutions. An excellent paper by the Zero Carbon Hub highlights that this still remains very demanding and unrealistic for some house types. The recommendations in that report suggest the following carbon compliance levels:

  • 60 per cent for detached houses
  • 56 per cent for attached houses
  • 44 per cent for low-rise apartment blocks.

Describing Allowable Solutions

‘Allowable Solutions’ has been a useful catch-all term for any approved carbon-saving measures that would be available to developers from 2016 to allow for the carbon that they would not normally be required to mitigate on site through Carbon Compliance (see illustration).

The expectations that have become associated with Allowable Solutions are:

  1. That the developer would make a payment to secure emissions reductions through (largely) near-site or off-site, carbon-saving (Allowable Solutions) projects;
  2. That, independent of the developer, there would be an opportunity to aggregate a number of Allowable Solutions payments to deliver larger scale carbon-emission reduction projects;
  3. That Allowable Solutions would be affordable and (per unit of carbon) would cost, at least initially, less than Carbon Compliance;
  4. That wherever possible, Allowable Solutions would be linked with local projects that would bring local benefits.
Zero carbon comliance
Zero carbon comliance

The carbon compliance percentage achieved on any project will be determined by the efficiencies achieved by the building fabric and building services plus any on-site low or zero-carbon energy source.

In the original proposal for the zero carbon standard there were no specific building fabric efficiency targets. This was addressed in the (2010) Code for Sustainable - Homes: Technical Guide, which set a new criterion, the Fabric Energy Efficiency Standard (FEES), for the dwelling's space heating. Since the zero carbon standard for new homes is not to be enforced until 2016, FEES is likely to be developed further before then. At the time of writing, it helpfully introduces a Passivhaus-style space heating energy target - for the first time moving away from a carbon emissions measurement.

We feel this is a positive development. The lower the space heating target you can achieve, the less you need to make up to meet the overall carbon compliance percentage. Reducing the on-site carbon emissions through excellent fabric performance is also key to reducing the need for additional and expensive on-site energy production. Energy generating systems will also have a shorter expected life (a solar hot water system, for example, will last 10 to 25 years) compared with the general building fabric (average 60 years), so prioritising investment in fabric makes good sense.

For the zero carbon level, the FEES target is (currently) 39-46kWh/m2.a. The range reflects different house types - for example, it is easier to improve performance on a mid-terrace than on a detached house. The UK's Standard Assessment Procedure (SAP) method for measuring floor area is more generous than that of Passivhaus which means that the zero carbon target is actually equivalent to over 50kWh/m2.a in Passivhaus terms. The consultation for the next updated Building Regulations, Part L (2013) is also proposing an interim Target Fabric Energy Efficiency (TFEE) requirement for new dwellings, of 43-52kWh/m2.a, adopting the same measuring standard as the zero carbon FEES levels. As yet there is no final decision on the standard they propose to adopt - the TFEE or full zero carbon proposed FEES levels. Whichever is adopted will then also link into Level 4 of the CSH. The interim TFEE would apply from 2013 until 2016.

Fabric performance and ventilation strategies

The zero carbon space-heating target range is clearly less stringent than that of Passivhaus (at l5kWh/m2.a), and this reflects a reluctance to limit ventilation strategies to MVHR. There is a body of opinion that advocates natural ventilation solutions such as passive stack ventilation(a whole-house ventilation system that uses naturally occurring pressure differences to draw air in through trickle vents in windows and then up and out through ducts in the kitchen and bathrooms). This necessitates higher air-leakage rates, which come with a significant energy penalty. The air-leakage benchmark for zero carbon is being currently mooted at an air permeability of 3m3/hr/m2, This is approximately equivalent to 3ach (air changes per hour) for an average-sized house. There has also been discussion regarding the capability of the general construction industry to achieve very low air change rates, i.e. below 3ach. This compares with the Passivhaus standard of 0.6ach - again, a far more stringent standard.

Without mandatory fabric energy targets, there was an early tendency for those looking to meet the zero carbon standard to rely on relatively complex and hard-to-maintain low-carbon heating solutions to achieve the carbon emission reductions. This concentration on renewable technologies can easily lead to a less informed focus on building fabric, which will increase other risks. By beginning to increase levels of insulation in our homes and making them much less 'leaky', we are changing the way they physically behave, and an understanding of this is key. Making radical changes without understanding carries four major risks:

  • reduced indoor air quality (IAQ)
  • moisture within the fabric causing mould and deterioration of materials (and exacer­bating the risk of reduced IAQ)
  • unacceptable overheating in summer
  • underperforming buildings (in energy terms).

Introducing FEES will - rightly - refocus on the building fabric, but this will need to be coupled with appropriate modelling methods and training so that these changes in building construction do not lead to the risks just noted. Linking the required measurements to as-built performance (measuring real performance after occupation), rather than design performance (using energy modelling software during design), as now recommended in the zero carbon consultations, will assist with this.

A zero-carbon Passivhaus

There is a misconception that Passivhaus "will only get you to L4 (Level 4) of the Code for Sustainable Homes". If you built a Passivhaus and chose not to address any of the other sustainability criteria assessed in the CSH, then this might be true. In particular, Passivhaus does not include the water usage criteria demanded by Level 5 and Level 6. However, if water usage is addressed in a Passivhaus design, it should comfortably meet Level 5.

In fact it should be easier and cheaper to meet a zero carbon standard in a Passivhaus than in a structure that is not designed as a Passivhaus. This is simply because the building fabric of a Passivhaus leads to the exceptionally low energy requirement for space heating, even relative to a zero-carbon house

The Passivhaus standard also includes a total primary energy demand of 120kWh/m2.a, which will also help to achieve zero carbon because it encourages efficient energy use across all electrical appliances and uses within a building.

Together, this means that if regulated and unregulated carbon emissions are taken into account, a Passivhaus can reach a zero carbon level with minimal additional renewable devices. If regulated emissions only are considered (the current zero carbon definition), a Passivhaus has been shown to achieve a 65- to 70-per-cent reduction in regulated carbon emissions compared with a compliant Part L (2006) dwelling, when calculated using the PHPP, without the use of any on-site low- or zero-carbon energy provision. This meets all the current zero carbon 'carbon compliance' recommended emissions reductions (44, 56 or 60 per cent). In making a comparison between Passivhaus and zero carbon, it should not be forgotten that, by using the PHPP and applying Passivhaus methodology, a much more reliable prediction of real-life performance is achieved. And the Passivhaus also addresses summer overheating risks and IAQ (Internal Air Quality) much more reliably than a non-Passivhaus low-energy building.

Even where a project aim is to achieve zero carbon, it is worth giving serious consideration to using the PHPP and applying Passivhaus methodology and principles to the building fabric design, i.e. to meet or, even better, to exceed, the FEES target. There are many efficiency gains and no conflicts.

Broader sustainability criteria

As we have seen from the issues relating to ventilation strategies discussed above, the Passivhaus focus on building fabric performance, and scientific research into and testing of this, is critically important. The fact that other sustainability criteria are not included as part of the Passivhaus standard has ensured that this focus has been maintained. This is not to say, however, that other sustainability criteria apart from carbon emissions (which zero carbon focuses on) and energy in use  (which Passivhaus focuses on) are not important: the fact is that Passivhaus buildings can be made from many different materials and construction methods (both lightweight and heavyweight), and the Passivhaus standard is perfectly suited to combining with more diverse sustainable assessment systems. Unfortunately, official certification using two different assessment methods on one building will have cost implications, but in technical terms there is no inherent incompatibility between Passivhaus and other systems, such as the CSH or BREEAM, or the US systems LEED and HERS. Other standards can usefully widen the Passivhaus approach to consider some broader sustainability issues, including recycling, water management and 'Lifetime Homes' recommendations.

On-site low- or zero-carbon energy

While a zero-carbon Passivhaus may not require any or only minimal on-site or zero-carbon energy for carbon compliance, you may still want to consider such options. If the aim is only to meet the zero carbon FEES targets (not the full Passivhaus target), then some on-site or zero-carbon energy will be essential. (‘Zero-carbon energy’ normally refers to biomass fuel, while 'on-site' refers to energy generation.)

Carbon compliance
Carbon compliance

Zero Carbon Homes as defined by the Code for Sustainable Homes

Our built environment accounts for over half of our carbon dioxide emissions. We now have the Code for Sustainable Homes (CSH) to help designers and builders of new homes in the UK. But will it help or hinder? In April 2008 the government launched the Code for Sustainable Homes (CSH), calling it a 'step-change in sustainable home building practice'. The scheme that it replaced, and that it is modelled on (EcoHomes) failed to capture the imagination of the very conservative house building industry outside token projects, that were blessed with government funding and housing associations. Unlike EcoHomes though, the CSH feels much more like a mandatory, rather than an optional code. In fact they did a lot more than that because at the political level, at the time of its introduction, we were at the pinnacle of a housing boom, with massive demand for homes and a lot of potential new housing sites hanging in the balance.

The government used this almost unprec­edented demand to throw down the challenge. Permission would be given for new sites as the incentive (new eco towns), but adoption of the CSH is the mandatory side. Essentially, the feeling was that any volume builder, who could prove to be singing from the 'zero carbon home' song sheet, could expect to be favoured with easier planning permission. It sounded good for the shareholders, good news for home buyers and good news for the environment. But is it?

Well the answer has to be a guarded 'yes' because it has captured the imagination of many mainstream developers and the industry as a whole. However, on the downside, since the launch of the CSH we have seen unprec­edented levels of greenwashing. The most striking example is that many, very ordinary building products are being re-branded green, purely based on the assumption that they could be used in projects built to the CSH stand­ards. No Code level is mentioned but let's not forget that Code level 1 is barely better than current Building Regulations! Another example is industry trade groups claiming that all their members are now zero carbon but merely on the back of carbon offsetting! Are they now CSH compliant?

The true definition of 'zero carbon' has yet to be properly defined and big players in the industry have recently discovered that they may have bitten off more than they can chew by going along with the government's rallying cry of 'zero carbon by 2016'. This is an impossible goal and doomed to failure from the beginning, but we need to watch this space over the next couple of years for a further re-definition and a probable watering down of what 'zero carbon' actually means. For the time being though see the table below for the present definition. One concern is that it will get diluted in its requirements but not in name. For instance, there is a proposal on the table suggesting that builders who are unable to meet the zero carbon target by that time will be allowed to pay a fee. A fine, if you like, which, it is touted, will be used for carbon offsetting elsewhere. Therefore, one word of warning before we go on, what you read here may well not be what will actually be required in 2016.

Who it affects

Housing Association funded projects 2008-2012 Code level 32013-2015 Code level 4 Likely to require code level 6

Everyone else via Building RegulationsAssessment mandatory for all dwellings25% carbon improvement44% carbon improvement (below 2006 Building Regulations baseline)Proposed zero carbon homes

Another, more subtle and perhaps overlooked aspect of zero carbon is that, If aiming for level 6, builders (site owners) are having to enter the power generation business at a hopelessly uneconomic scale, which somewhat ignores the efficiencies of the renewables obligation certificate system (ROCs). At present it seems that on-site renewables will be eligible for tradable ROCs, which effectively renders them part of the national renewable generation grid and despite being on-site, adding nothing, or very little, to the national total. Feed In tariffs (that have proven so successful in other European countries) to encourage more on-site generation, may well have been a better route towards 'zero carbon' than ROC's, certainly at this small scale where plant costs are high and returns are low.

Zero carbon is not the only problem facing anyone wanting to achieve Code level 6. When you get to that level other difficult requirements also kick in, some of which are step-changes, such as increasingly stringent water use restrictions. The SAP (standard assessment procedure) software that forms the basis of the Part L of the current Building Regulations also underpins the energy category of the CSH.

Background to the CSH

The CSH was developed, at least in part, in response to the European Parliament's Directive 2002/91/EC on the energy performance of buildings, itself a response to Kyoto. In 2006 the government announced the 10-year timetable towards a target that all new homes from 2016 must be built to 'zero carbon standards'. This would be achieved through a step by step tightening of the Building Regulations. Since April 2007 the developer of any new home in England could choose to be assessed against the Code.

On the 16 November 2007 the government confirmed that it would be proceeding with the implementation of mandatory ratings against the Code for all new publicly funded homes, following responses to the consultation on making a rating mandatory. From May 2008 all homes built in England need to be rated to the CSH.

 The ‘zero carbon’ home (as defined in the code)

A zero carbon' home is where net carbon emissions resulting from all energy used in the dwelling is zero. This includes the energy consumed in the operation of the space heating/cooling and hot-water systems, ventilation, all internal lighting, cooking and all electrical appliances. The calculation can take account of contributions from renewable/low carbon installations on/in the dwelling, or provided by an energy services company (ESCO) on/offsite, provided it directly supplies the dwelling. Alternatively it is acceptable to include, in the estimate of carbon emissions, the contribution from 'accredited external renewables, For a true zero carbon home, it will also be necessary to ensure that the fabric of the building significantly exceeds the standards currently required by Part L of the Building Regulations. 2000 (as amended). The 'heat loss parameter' (covering the walls, windows and other elements of the building design) must be no more than 0.8W/m2K.

CSH uses the SAP (standard assessment procedure) computation which takes into account energy consumed through heating, lighting and hot water provision. Homes will have to reach zero carbon for these factors using the SAP computation. Heat and power for this element must be generated either in the home, or on the development, or through other local community arrangements, (including district heat and power) and must be renewable (i.e. non-fossil fuel) energy. A zero carbon home is also required to have zero carbon emissions from use of appliances in the homes (on average over a year). SAP does not contain any provision for energy consumption of appliances but will be updated to do so in due course. Until SAP is updated the 'appliances' element of the qualification will be that each home must provide an amount of renewable electricity equal to a specified amount of kWh per metre squared of floor space. This additional power must be renewable power, produced either within the area of the building and its grounds, elsewhere in the development or beyond, as long as the developer has entered into arrange­ments to ensure that the renewable generation is additional to existing plans. The amount of such additional power can be reduced by any surplus from the arrangements to meet zero carbon on heating, hot water and lighting.


The exception to the Rule - Wimbish Passive House Scheme

Architects visual of the site

Architects visual of the site

Norfolk-based Parsons & Whittley architects employed Passivhaus principles in the design of what is set to be the UK's first rural affordable housing scheme to gain Passivhaus certification At first sight, the 14-dwelling Hastoe Housing Association development underway in the village of Wimbish, Essex, looks like many other small schemes of its type, but take a closer look at the design and detailing and it becomes clear that this could in fact be a blueprint for such developments in years to come.


Aiming for completion in Spring 2011, the green­field scheme is being built under the 'exception site' policy to address local housing needs, with funding from the Homes and Communities Agency and investment from Hastoe. People will require strong local connections to be housed and no-one will be able to buy more than 80% of their home.

Besides providing much-needed affordable homes for a rural community, the scheme is also aiming for high levels of sustainability, a potential way forward in addressing the pressing issue of fuel poverty, as well as addressing climate change concerns.

The houses:

- a mixture of homes for rent and shared ownership

- are designed to be super energy-efficient, and will not only comply with Passivhaus principles but also meet the demands of Level 4 of the Code for Sustainable Homes.

Passivhaus standard buildings retain the heat created within the dwelling as well as from passive solar gain, eliminating the need for central heating and reducing fuel costs. The standard requires very high levels of insulation (in order to meet U-values of below 0.15W/m²K for walls, roof and floor), a design that makes the most of solar energy, and superb sealing throughout.

Promoted by the Passivhaus Institute in Darmstadt, Germany, there are around 25,000 Passivhaus buildings worldwide - the vast majority of them in Germany and Austria. The approach is rapidly growing in popularity in the UK as developers and designers strive to meet zero-carbon targets.

Of course, Passivhaus standards were originally developed against European norms - where floor areas tend to be larger. Adapting the standards for affordable housing in the UK, where floor areas are smaller due to cost and space pressures, means careful consideration must be given to design. It can also mean raising the bar on materials performance in order to meet required elemental values and airtightness demands.


Parsons & Whittley's design for the development - which is being built by Passivhaus construction expert Bramall Construction and

assessed, against Passivhaus standards by specialist consultancy Inbuilt - is simple without unnecessary steps and staggers, which add to the heat loss area and complicate the design and construction process.

A number of construction options were evaluated before finally adopting 190mm solid aircrete external walls wrapped externally in 285mm of Neopor rendered insulation. With insulation running under the reinforced concrete ground floor slab, and conventional standard trussed rafter roofs supporting 500mm Crown Loft Roll, the construction details have been kept simple and effective, meaning they can easily be replicated at future sites.

Key to effective insulation of the buildings was the specification of Dow Building Solutions' Floorrnate 300-A Styrofoarn-A insulation to run below the entire concrete floor slab of the structures. lnstalling insulation below the slab helps to create an 'envelope' of continuous insulation, which minimises heat loss, requiring a material that can maintain strength and good thermal performance even when used externally.

Floorrnate 300-A has a design load of 130kN/m2 and is highly durable, with excellent moisture resistance and compressive strength, enabling the insulation to perform outside the waterproofing envelope.  Installing insulation below the slab also helps to avoid thermal bridges at floor and wall junctions, and makes the most of precious internal space, meaning it is fast becoming recognised as an effective way of insulating new buildings.

Dwelling forms have been kept deliberately simple at the Hastoe development to avoid thermal bridging risks, and porches, meter boxes and brise soleil are all independently supported to avoid penetrating the insulation overcoat. East-west orientation of the blocks facilitates passive solar gains, with careful attention to shading to avoid summer overheating.

The design and construction methods also assisted the incredibly low airtightness requirement of 0.6 air changes per hour, with internal wet plaster providing the majority of the barrier, and all joins covered in specialist membranes or tapes.

Furthermore, specialist thermal modelling was undertaken by Inbuilt to calculate thermal bridges and advise on the impact of small changes to the design. For example, the crucial impact of small changes to window designs was modelled in advance to help value-engineer the project and feed into the specification of future sites. Everything was detailed at 1:2 in order to convey the importance of airtightness and to assist the accuracy of the Passivhaus Planning Package (PHPP) modelling.

Of course, design and build is one thing, but the dwellings also need to stand up to the rigours of everyday life. The choice of servicing strategy had to balance familiarity for residents, availability of components, client requirements and cost, and conventional gas boilers were eventually selected. These are being coupled with large thermal stores to prevent cycling, and will be supplemented by solar thermal systems. The thermal stores will supply domestic hot water as well as feeding top-up heat via a duct heater into the air supplied by a heat recovery ventilation system.

As well as following Passivhaus principles in order to gain certification and following Level 4 of the Code for Sustainable Homes, Brarnall is building the Wimbish development to: the Homes and Communities Agency's 'Design and Quality Standards and Strategy'; the Joseph Rowntree Foundation's 'Lifetime Homes' standard; and the Commission for Architecture and the Built Environment's 'Building for Life' standard.

The Passivhaus Standard


The Passivhaus standard offers a well-established alternative to the Code for Sustainable Homes and the Building Regulations for sustainable design and construction. Denise Freeman investigates the emergence of Passivhaus in the UK and the benefits of external wall insulation and modern render systems. The term Passivhaus relates to the rigorous energy-efficient building standard developed in Germany in the late 1980s. Although it is considered to be a relatively new standard in the UK, Passivhaus is widely used throughout Europe. 17,000 buildings have been constructed using its design principles. The core focus of Passivhaus design is to achieve an extremely low-energy building that requires little energy for space heating and cooling. Buildings built to Passivhaus standards typically achieve a 44% reduction in carbon emissions compared to an average existing home.

Passivhaus is sometimes confused with Passive House, which typically relates to a building with traditional passive design features, such as the use of solar gain. Whilst Passive House design relies exclusively upon the orientation of a building and format, and uses fewer or no active mechanical and electrical systems. A Passivhaus building integrates some passive design features, but takes an active approach rather than a passive approach. In essence, the fundamental space-heating requirement in a Passivhaus building is managed by a mechanical ventilation and heat recovery system. This active approach also allows the Passivhaus designer to be more flexible with the building design. Current legislation stipulates that new build homes should achieve a minimum of level 3 under the Code for Sustainable Homes. However, this is soon set to increase with all new builds having to comply with code level 4 by 2013. Passivhaus is equivalent to code level 4. The sustainable methodology behind Passivhaus brings the housing sector a step closer to the government's zero-carbon idea, which is almost impossible to achieve without implementing Passivhaus principles.

Core Elements

A Passivhaus building must incorporate a number of core elements including exceptional levels of insulation, an airtight envelope, a heat recovery system and thermally advanced windows and insulated doors. In order to realise the extremely high levels of thermal performance that the Passivhaus standard requires, the external walls must achieve a U-value rating of <0.15W /m2K. This is achieved through the use of an external wall insulation (EWI) system. EWI systems are increasingly becoming a key element in the specification process with regards to high thermal efficiency requirements. Around 30% of the energy used to heat a typical home is lost through the external walls. EWI systems work by wrapping the building in a thermally efficient envelope, significantly reducing any energy loss. maximised and comfortable internal maintained all year round.

Specialised Performance Actual Performance of Green Building (the specification trap)

For those who would prefer a very highly efficient house in a more traditional mode, volume house builder, Miller Homes, has constructed an allegedly zero-carbon home as part of an ordinary commercial development, and the house is available for sale. It is one of 5 built to different CSH levels as a pilot project by the company in Basingstoke. A spokesman said it had been a huge challenge, technically and financially. The properties will be monitored using smart metering as well as sensors to monitor humidity for a period of 12 months after completion. This will give a better picture of the reality of living in an airtight, “zero carbon” home, as well as being able to gauge the most and least effective of the new technologies employed. When the results are clear, Miller says it intends to build more. Hopefully these prototypes will be more successful than the Stewart Milne Group's Sigma home at the BRE Innovation Park. Research conducted over a year, and four periods of evaluation when the home was occupied by a real life family, has resulted in the developer going back to the drawing board. The evaluation showed a need to concentrate on primarily low energy (highly insulated) homes rather than using bolt on microgeneration technology and aiming for theoretically zero carbon structures by producing the necessary power onsite. The company found their add-ons, such as wind turbines, photovoltaic panels and solar thermal, did not consistently deliver the required performance levels.

One of the major problems with the original structure was the under performance of the building envelope. Although built to a higher specification than a normal house, it was found to be 40% less efficient than

Meanwhile, in a similar vein, some serious flaws in the energy calculations used for the Code for Sustainable Homes have been revealed after research by Jim Parker on the current Denby Dale Passivhaus project in West Yorkshire. Parker has concluded that 'a Passivhaus dwelling's energy savings are not realistically represented by its Code for Sustainable Homes ratings'. The building would only meet CSH level 3 criteria for Ene 1: Dwelling Emission Rate, the mandatory aspect of the Code's Energy Category, despite its being projected to be one of the most energy efficient buildings in the UK.

All buildings meeting the strict Passivhaus standards must have space heating requirements of less than 15kWh/m2/year, and use up to 90% less energy to heat than standard UK homes, often requiring minimal or no heating.

In addition, airtightness for Passivhaus buildings, such as that at Denby Dale, is required to be no more than 0.6 air changes at 50 Pascals. The report points out that many buildings receiving higher CSH ratings (up to level 6) actually perform worse than the Denby Dale Passivhaus in terms of space heating requirements and airtightness, but gain points in other areas, and sometimes through the use of inefficient and expensive bolt-on renewable technologies. It's a pity this research wasn't available to the builders of the prototype homes mentioned above.