An outstanding issue: The Performance Gap

An outstanding issue: The Performance Gap

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… So I made it my mission to find out what [they were doing wrong] and to establish what was needed to do it right.

Passivhaus Overheating: Design it out

Passivhaus Overheating: Design it out

Passivhaus overheating shouldn’t happen: it’s one of the criteria of the international Passivhaus standard. Even so, people sometimes ignore this requirement during the early stages of the design process.

Ground-breaking housing scheme captures one developer's journey to passive ...

Ground-breaking housing scheme captures one developer's journey to passive ...

Ground-breaking housing scheme captures one developer's journey to passive ... The just-finished second phase of Durkan Residential's ambitious Silken Park scheme in south-west Dublin bridges the gap between two extremes: while phase one was built to the 2002 building regulations, phase three - which will break ground next year - will comprise 59 passive certified units.

Passive homes move is active step towards carbon neutral future

Passive homes move is active step towards carbon neutral future

It’s a glorious day: Dun Laoghaire-Rathdown county council has passed a motion to make the passive house — and its equivalent — mandatory for all new buildings.

Dún Laoghaire council defies Alan Kelly on passive houses

Dún Laoghaire council defies Alan Kelly on passive houses

Dún Laoghaire-Rathdown County Council could be on course for a clash with Minister for the Environment Alan Kelly after councillors voted in favour of an energy-efficient building standard over which his department has serious concerns.

The case for making Passive House mandatory

The case for making Passive House mandatory

There is a growing sense that passive house's time has come. Following on from the examples set by umpteen municipalities and local authorities in continental Europe, there are signs of public bodies in Ireland and the UK making the passive house standard mandatory.

The embodiment of low carbon

Now nearing completion, the University of East Anglia's (UEA) most recent development, The Enterprise Centre, is on course to become an exemplar low-embodied carbon buildinq, pushing the boundaries for sustainable architecture.

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).

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.


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

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.


Eco houses a good or bad idea?

What is an Eco house?

Architect Paul McAlister

Architect Paul McAlister

The name is banded around and is ultimately misunderstood by the general public. It has also become a generic term encompassing all things ecological and sustainable in terms of building and living in an environmentally friendly home. There is actually no simple definition of an eco house and it could be said that any house which incorporates technology, such as renewable energy solutions, may be considered an eco house to a degree. Another ‘Green’ concept would be to build a house using some overtly ‘green’ material such as sheep’s wool insulation or straw bales for insulation of the external walls. The commitment to build in these greener materials indicates a strong statement in terms of the ‘greenness’ of the build but without a holistic approach to the dwelling the green opportunity of building a new dwelling may be lost.

The global problem of build-up in CO2 gases in the atmosphere and the knock on effect of global warming, and damage to the ecosystem, is a manmade phenomenon which needs to be addressed for a sustainable future.

In the UK 30% of CO2 is produced as a result of the energy requirement of the housing stock, which means the homes, that we all live in, produce a significant amount of all CO2. Governments have recognised this and have a target, enforceable by building regulations, for all new homes to be carbon neutral by 2016. This would be achieved by a series of incremental increases in the energy efficiency of dwellings and the increased use of renewable technologies.

The energy efficiency of dwellings is therefore the one area in which the individual may play a major part in reducing their ‘carbon footprint’ making a contribution to reduce CO2 emissions.

An added benefit of an energy efficient home is the actual running costs of the house itself. An initial capital investment providing a super-insulated envelope for the building and suitable means of energy efficient ventilation may have a payback period of 5-10 years, depending on specification. After this period the house is saving money for the occupiers, as it is possible to design passive houses that need no additional heat source except in severe weather conditions.

If we identify energy efficiency as one of the key elements in environmentally friendly building design then it would seem appropriate to focus on this area, as a key element in the design and specification, were the correct choice of building materials and construction techniques will make a significant contribution to the home. The use of renewable energy sources also has a role to play and the investment of relatively common technology, such as solar panels for hot water heating, should be considered for any new home striving to be energy efficient.

The other element of Eco build that makes an environmental impact is reducing water supply needs by recycling of rainwater from roofs. This water is stored and reused for washing and flushing toilets whilst the waste produced from the home may be filtered by reed beds.

Finally the choice of material to construct the eco home brings more choices to be made in terms of Green materials. The concept of embodied energy, the energy required to produce the material, becomes a deciding factor and also the amount of CO2 used in the production of the material. The use of timber as a building material, from sustainable and managed forests, is an obvious ‘green’ material as the trees themselves absorb CO2 when growing. The use of recycled or natural material also has environmentally green credentials. The judgement may come to personal preference or the financial implications of some of the less mass produced products may make their use prohibitive.

In the end market forces and government legislation will determine changes in building design. There is a strong argument to future-proof new dwellings for the lifetime of the home occupier and for generations to come. This investment will ensure a sustainable future for our housing stock and makes the Eco house concept one that becomes the prudent benchmark of new homes.

Paul McAlister

Passive houses will be Industry Norm

IF you are building or renovating a house you will inevitably hear the term ‘passive house’ or ‘passivhaus’, the word ‘passiv’ with a Teutonic clip of its ‘e’. For the uninitiated, this term, and the cheery declaration of ‘passivhaus standard’ slapped on a range of energy-efficient products, can be confusing. Passivhaus standards, or an approximation, will increasingly become the industry norm for house building, as all new homes are constructed to be carbon neutral, emitting no harmful gases as we heat our rooms and water.

Turn up the body heat

or a house to be deemed passive, it must draw a minimal amount of active external energy, if any at all (excluding solar), to run its space and water heating and keep it cool, where needed. Passive houses are sometimes termed ‘body heat houses’, as the warmth emanating from the people who live there, and the passive heating coming through the windows, is enough to keep them cosy.

In their most developed forms, these sustainable houses can become very active, selling energy back to the national energy grid. If you want to find out more about energy-positive housing, Google ‘Villa Åkarp’, the first of a new league of super homes constructed in Malmø Sweden.

Setting the standard

The energy standard for the true Passivhaus, is set by the PassivHaus Institute in Germany, and despite its rigorous demands, it remains a building concept not a brand. The concept was developed by Professors Bo Adamson of Sweden, and Wolfgang Feist of Germany and the first Passivhaus dwellings were constructed in Darmstadt in 1991. The criteria for a passive House per m² living area include a maximum of 15 kWh/m²yr annual space-heat requirement and no more than 42 kWh/ m²yr annual total amount of energy input.

A semi-detached, two storey Irish house built in the mid 1970s before the introduction of thermal insulation standards would have a space heating requirement of over 200kWh/m²yr and have a total primary energy demand of over 400 kWh/ m²yr. In short the energy efficiency of the Passivhaus is 90% better.

Highly insulated

A passive house is highly insulated throughout every centimetre of the envelope, including walls, roof, floor slab, windows and doors, and has no ‘cold-bridging’ where heat jumps across one material to another. It’s air-tight to prevent thermal loss and uncontrolled air ingress. The ventilations is carefully managed through a mechanical and heat ventilations system, abbreviated as a MHRV (75% of the heat from exhaust air is transferred to the fresh air by means of a heat exchanger). In warm weather the Passivhaus will use passive cooling techniques, including strategic shading. A successful build means a comfortable temperature year round, healthy humidity, fresh, clean air, no draughts whatsoever and laughable fuel bills.

Passive House
Passive House

Setting the standard

Certified passive houses have been built here in Ireland since 2005 to the correct layout and orientation and with the key materials and techniques, achieving Passivhaus energy performance through a highly exacting, rigorous build. Retrofit projects (which have different Passivhaus standards) are also becoming very popular. When developing new housing, or renovating existing house stock, builders have been enthused to reach beyond the building regulations towards near passive standards with low-energy designs and materials. There are actually only 20,000 certified Passivhaus builds in the entire world. If something is certified fit to go into a Passivhaus (when perfectly installed), you can be fairly sure it’s top notch in terms of its insulation properties for example.

Passivhaus Beats BER

An energy efficient BER ‘A’ rated house shares a lot of common ground with a Passivhaus. However, an ‘A1’ rated house in BER terms is not necessarily worthy of Passivhaus certification, and a Passivhaus may not reach a BER ‘A1’ rating, as the two are surveyed using different methods. The only downside voiced by the industry for passive builds is in terms of the increased cost to build and one or two lifestyle challenges. The whole house is at one temperature for example, annoying if you prefer a cool bedroom and warm living room.

Worth the expense

If you’re keen on building a Passivhaus or renovating your home to as close to passive standards as possible, the capital investment will be greater. For renovations the layout of the house may have to change and improving the insulation performance of the entire house will be vital. However, the long range rewards in terms of running costs and the potentially increased value of a superbly well built house make it well worth consideration. Part ‘L’ of the Building Regulations has done a lot to pull new housing and improvements towards high energy efficient buildings. Exceeding the standard and aiming for passive or near passive performance is a sound guiding principle.

By Kya deLongchamps

House Design relieves the misery of Hay Fever

Architect Paul McAlister

Architect Paul McAlister

Cooking steaks on the barbecue, mowing the lawn or taking a walk in the countryside – all normal summer pursuits for many people.  But, for hay fever sufferers, the thought of uncut grass sends them rushing indoors.  Over 15 million people in the UK have hay fever and 95% are allergic to grass pollen. But what’s the alternative to a summer of sneezing, a runny nose and watery eyes apart from a box of tissues, antihistamine tablets or moving to the Sahara Desert?  Believe it or not, building a new home with “hay fever prevention features” may be part of the answer.

“Triple-glazed windows are very effective at keeping grass pollen out of the house in the first place but a unique ventilation system makes the biggest impact.  The hay fever sufferer then has a ‘pollen free oasis’ to live in,” explains Portadown architect Paul McAlister, Northern Ireland’s first Passive House Designer.

A Passive House is a specific approach to energy efficient homes, originating in Germany (Passivhaus).  The key features are super insulation, extreme airtightness, triple-glazing and a mechanical ventilation system.

“One of the key features of a Passive House is the airtightness requirement meaning windows do not need to be opened for fresh air.  Instead, a clever system called Mechanical Ventilation Heat Recovery supplies and circulates fresh filtered air 365 days per year.  The filters used are very fine and they stop minute particles of pollen from getting into the house making it a ‘pollen-free zone’ for the hay fever sufferer.”

Up to 80% savings in energy costs can be made by living in a Passive House even though the ventilation system uses electricity as a power source.  Heat is collected from the air leaving the house and this energy is then reused to heat incoming fresh air.

“I find the summer months a real challenge whether I’m indoors or outdoors, “ commented James Ervine, a chronic hay fever sufferer from Bangor.  “Even though I shut the windows and remain in a cocoon for several months, my eyes still itch and my nose runs.  The Passive House design sounds ideal for someone with my condition and I will definitely consider this approach when I build a new home in a few years’ time.”

So watching the high pressure settling over Northern Ireland doesn’t have to bring tears to the eyes of the hay fever sufferer any longer.  If you’re planning to build a new house and struggle with hay fever every summer, it’s well worth investigating the Passive House technology.

Author Paul McAlister

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.

Passivhaus vs Code for Sustainable Homes

Many people appear confused about how PassivHaus and the code for sustainable homes can run in parallel, 'Does one compliment the other?’

To obtain the definitive answer, we need to remember that us that Passivhaus focuses on building fabric and performance without the use of renewable technology. Typically a PassivHaus will achieve code energy rating of level 4 or 5. This means that it is an ideal methodology for achieving the higher level of the overall code rating, whilst also minimising the cost of renewables.

Principles And Performance

The term 'PassivHaus' refers to a specific construction standard for buildings which have excellent comfort conditions in both winter and summer. These principles can be applied not only to the residential sector but also to commercial, industrial and public buildings. For houses, it is claimed that this is the world's leading standard in energy efficient construction. They are designed and built using a step-by-step approach with efficient components and a whole house ventilation system to achieve exceptionally low running costs to create something which is comfortable, healthy and sustainable.

There's an interesting article in Green Building Magazine written by Justin Bere about a talk given in London by Wolfgang Feist who founded the German PassivHaus Institute in Darmstadt.

The fundamental objective of PassivHaus design is unambiguously to cut energy consumption and to provide accurate design tools to measure the expected energy consumption in a clear, accurate, numerical way. Germans really don't have time for vagueness and are aware of the requirements set out in UK Building Regulations. However many of our Code level features are incorporated, no one can circumnavigate the essential requirement to produce a building designed to use less than 15kWh/m2/annum supplementary heat and no more than 120 kWh/m2/annum primary energy [total of heating, lighting, hot water, appliances and any cooling). No box ticking wood chip boiler - nothing will let the PassivHaus architect, developer or builder circumnavigates this fundamental, verifiable bottom-line requirement for PassivHaus certification.

The simple techniques necessary to achieve PassivHaus design are: Insulation [typically 30cm thick]; PassivHaus windows [airtight, triple glazed with thoroughly insulated frames achieving an overall U-value of 0.8 including the frame]; Airtight construction [max 0.6 air changes/hr under 50 pascals pressure] with very efficient mechanical heat recovery ventilation. Assuming that these three main performance targets are met, together with detailing to eliminate cold bridging and numerous other detailed requirements prescribed by the PHPP software, it is possible to eliminate the need for a boiler and the need for radiators or underfloor heating.

Comparing certain other UK building codes with the PassivHaus approach highlights difficulties in the UK codes that have been introduced in relative haste. By contrast the PassivHaus code has passed the test of time and Dr Feist is very careful to ensure that it remains truly robust. It is the very robust nature of the concept and the software that led the RIBA in a sustainability review to originally describe PassivHaus as 'The emerging European Standard.' Now there are about 17,000 buildings have been constructed worldwide, typically achieve an energy saving of 90% compared to existing housing principles.

The NHBC Foundation and Zero Carbon Hub have published 'A practical guide to building airtight dwellings'. It brings together the experiences of those who have already got to grips with air tightness for the benefits of designers and builders who have not. It provides solutions for common air leakage paths. Clearly, changes in the Building Regulations have now made air tightness an issue which cannot be ignored.

The Denby Dale Project

Typically, PassivHaus buildings are built using timber-frame construction or blockwork wall with external render. Green Building Store has succeeded in adapting the PassivHaus approach to British traditional building methods - by creating the first certified PassivHaus in the UK to use traditional cavity wall construction. Earlier this year the Denby Dale PassivHaus project in West Yorkshire received its official PassivHaus certification.

The project - built by Green Building Store's construction division Green Building Company - has pioneered the combination of low energy PassivHaus methodology with standard British cavity wall construction and building materials. Bill Butcher, Director of Green Building Store, said, "We chose cavity wall construction because most British builders are familiar with the technique and materials could be sourced easily from any builders' merchant. Cavity wall also met Yorkshire planning requirements for stone exteriors and was affordable for our clients. In addition, masonry construction, including cavity wall, offers a 'cave effect' which acts as a thermal mass, helping to keep temperatures stable in winter and summer".

It requires minimal heating - using 90% less energy for space heating than the UK average; £141 K build cost for the 118m2 three-bed detached house. Green Building Store's technical film 'PassivHaus low energy building in the UK' for building professionals is freely downloadable from The 60 minute film covers all stages of construction of the Denby Dale project.

What are the challenges?

Achieving the required level of air tightness, minimising the risk through good design and specification.

Is it costly to build?

European experience suggests an extra 6% is likely. There are not yet enough UK houses to make a proper comparison, although BRE is advising on a London project which has achieved PassivHaus for the same cost as a typical social housing one.

Are PassivHaus products widely available?

Yes but windows have at present time to be imported; they have generally been the reason for higher costs.

Will adopting PassivHaus facilitate compliance with buildings regs and the Code for Sustainable Homes?

Yes. If a compliant design specification is derived from PHPP [the PassivHaus Planning Package] and transposed into SAP, a 30-45% improvement in carbon emissions can be realised - without the use of heat-pump, biomass or other low carbon or renewable technology.

Passivhaus: An Affordable, High-Efficiency Standard

The Passivhaus approach is neither a building style nor simply a new build­ing technology. It is simply a perfor­mance standard, the implementation of which requires a set of experiences, tools, and high quality components available to all building professionals. Various projects have shown that the standard can be met in a wide variety of climates and with a wide range of archi­tectural styles, construction types (masonry, timber, steel or concrete) and building types (single family homes, large apartment complexes, offices, schools  and more).

The PassivHaus performance stan­dard is ambitious and clearly defined: 15 kWh per square metre per year for heating and, if needed, for cooling, combined with an aggressive total pri­mary energy limit, resulting in energy savings of some 75 per cent as com­pared with existing European new build projects. The remaining energy con­sumption of a PassivHaus is so low that it can be easily and affordably met with regional energy resources. Even renew­able energy, somewhat more expensive than today's oil and gas, becomes an affordable and competitive option when the amount of energy needed is as low as it is with a PassivHaus.

While measures to increase energy efficiency do not come free of charge, a PassivHaus integrates these measures into components that are needed in every new building. Improving the quality of the building envelope, the services, and the on-site project implementation not only results in energy savings, but also ensures greatly enhanced structural integrity, thermal comfort and air quality as compared to existing buildings.

Halle 58 Architekten’s three family apartment complex in the outskirts of Bern

Halle 58 Architekten’s three family apartment complex in the outskirts of Bern

A residential building in Liebefeld, Switzerland by Halle 58 Architects took first prize at the 2010 Passivhaus Architecture Awards (ph: Christine Blaser).

In a PassivHaus, the focus is on the longevity of the components, which will add value to the building during its life­cycle. Additionally, the heating require­ment, especially in the UK's climate, will be so low that the heating system can be substantially simplified, thus reducing investment and maintenance costs. Most of the components in a PassivHaus are simple to use and easy to maintain, such as high quality insula­tion, high performance windows and efficient heat exchangers.

Last but not least, the PassivHaus Standard is not an abstract theory; it has been tested and proven time and time again. All that architects and engineers need in order to realise a PassivHaus is know-how. The International Passive House Association has been working with affiliates worldwide, such as the UK's PassivHaus Trust, to further PassivHaus knowledge. Additionally, PassivHaus edu­cational programmes are available in almost all European countries. In short, PassivHaus is the affordable, almost zero-energy building solution.

Welsh Passivhaus Social Housing Trials

In 2009 Bere Architects won a competition to design low cost houses for Wales which would showcase the Passivhaus concept and feature innovative measures for energy efficiency and eco excellence. The houses are now complete and open for visitors at Ebbw Vale (by appointment) Larch House and Lime House are the first Welsh Passivhaus social housing prototypes to be erected in Wales. both house types are certified with the Passivhaus Institute by BRE Wales. Larch House has been designed to achieve Code 6, 'zero carbon' of the Code for Sustainable Homes. It is a 3 bed Passivhaus designed to minimize annual heat demand (below 15kW/m2/yr) using extreme peak load climate data prepared by the BRE for this Heads of Valley site.

Much of the winter warmth in Passivhaus designs is derived from solar gains, but Ebbw Vale is 1,000ft up in the top of a valley, with cold and misty winters. The BRE's weather data for the site showed it was twice as demanding as both Manchester and Innsbruck, Austria. To keep winter heat inside, the insulation levels are very high (walls 0.095 W/m2K; floors 0.076 W/m2K; roof 0.074 W/m2K), and because of the relative lack of winter sun, compared to a lowland site, the windows are unusually large to maximize the solar gains from a bright overcast winter sky (55% of south elevation). This is the traditional design strategy for a Passivhaus, resulting in great comfort, tiny energy bills, and bright and airy interior spaces. However, for social housing, a solution to overcome the costs associated with large windows and retractable blinds were required, so subtle but crucial changes were made to the design.

Lime House achieves Passivhaus certification using a different method, based on keeping the heat load below 10W/m2 at any time. 10W/m2 is the maximum amount of heat that can be transported by a low energy heat recovery ventilation unit, and unlike Larch House, Lime House has no towel radiator backup heating. It results in a building that focuses on minimizing heat demand during the worst periods of misty, Welsh hilltop, winter weather with short, dark days and cold nights. In these conditions, solar gains are of little importance, and internal heat gains are more important. So south facing windows are reduced in size and the better insulation of walls dominates, with no more than 20% south facing glazing. A weather optimization graph determined that any more than 20% glazing would increase the peak heat load above 10W/m2.


If fuel costs go up 5% per annum, the Code 6, zero carbon Passivhaus, social housing prototype will be significantly cheaper after 50 years than when it was built (due to its negligible demand for fuel and the feed-in tariff), whereas a standard building regs house will have more than doubled in cost, due to fuel costs. Even with 2.5kWp photovoltaic panels, a Code 5 Passivhaus will have cost only £10,000 more after 50 years than when it was built. At today's fuel prices our Code 6 Passivhaus is calculated to earn the occupant £1,333 per annum.


Now, with some UK based cost data that shows how Passivhaus houses can be built to a low cost, with really attractive payback periods that make it look short-sighted not to spend a little extra to achieve a certified Passivhaus, compared to a basic speculative builder house. These Passivhaus buildings will also future-proof occupants and owners from high running costs and fuel poverty.

The house building system which rewards speculators (private householders and commercial developers) for greed, regardless of the financial and environmental cost to future generations and the timidness of successive government ministers to go further than skin-deep into the portfolios they hold, to understand and then to explain and legislate for the greater good.

Cost analysis

A cost comparison was done against the RICS/BCIS database for one-off detached houses on normal lowland sites (nearest comparison available):

• Cost of Larch House, Passivhaus built to Code level 6: cost of the one-off, 100m2, three bed house, with normal UK weather data (7-10% less than cost using Ebbw Vale weather data), and including £12,000 towards the cost of PV, a sprinkler system, large windows and external sunshade blinds = £ 1700/m2.

• Cost of the lime House (low cost) Passivhaus: 76m2, two bed Passivhaus: After adjusting the Passivhaus for lowland weather data (saving 7% costs) we found a Passivhaus built to the 2 bed Lime House spec costs £13641 (excluding PV) which is just 14% more than exact comparisons with RICS data for average ordinary one-off houses built over the last 10 years averaging a cost of £1171/m2, both excluding prelims and PV.

According to RICS figures, once built in quantities, ordinary estate housing, over the last 10 years, cost an average of £760/m2, excluding prelims and based on RICS data of the average price difference between one-off and estate housing. It should be possible for a large volume house builder to build Passivhaus estate housing of the (low cost) type, using the lime House design techniques for £886/m2. That means that for a 2 bed house of 76m2, the cost premium for a Passivhaus is £9,500.

The return on that investment is 14-17 years, based on assumptions of 5-10% annual fuel price increases, and the cost savings of the house over 50 years are likely to be more than £ 60,000, even with only 5% annual energy increases and without income from the feed-in tariff associated with photovoltaic's. For 10% price increases the figure would be £360,000.

Justin Bere