Passive house

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.

The Progress of Passive House

The Progress of Passive House

The energy supply market is rapidly shifting from fossil fuel to renewable sources. This transition is necessary, not only to comply with European targets and international and regional protocols on climate change (20% share from renewables on total energy supply by 2020), but it’s also the most responsible way to promote energy security.

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.

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.

Criteria for the Passive House, EnerPHit and PHI Low Energy Building Standard

Passive House is a building standard that is truly energy efficient, comfortable and affordable at the same time.  Passive House is not a brand name, but a tried and true construction concept that can be applied by anyone, anywhere.

The Passive House standard can't be diluted and here are the maths to prove it

The Passive House standard can't be diluted and here are the maths to prove it

“As debate ramps up in Ireland about whether local authorities in Dublin should adopt the passive house standard, and the UK government scraps its plans for zero carbon homes, Dr Shane Colclough urges passive house advocates to prepare for the lobbying battles ahead by remembering the basic science behind the standard.”

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.


Rosslare Passive House Scheme

Ireland has woken up to the Passive House. Seven years ago Tomas O’Leary built Ireland’s first certified passive house in Wicklow – a home that showed Germanic influences in looks as well as energy performance. A new development at Grange Lough, Rosslare, reveals that passive can be made Irish – both in terms of what they’re built with, and how they look. Grange Lough in Rosslare, Co Wexford is the country's first commercial passive house development, and as such it's a landmark in the story of Irish construction. This is the first time that a speculative developer has looked at the market and decided it wanted passive houses. Not only that, but the scheme represents perhaps the most Irish take on the passive house you'll find. Its design is traditional- it does not look German, and incorporates much of what you'd expect in an Irish house, even a chimney. Most especially however, it has been built using Irish products and Irish expertise.

The design team is Irish, the developer is Irish, the thermal envelope manufacturer is Irish, the company which is certifying the house as passive is Irish, and almost all of the technol­ogy used in the house - including the windows and doors - is Irish.

"The passive house is a German concept but I think it's very important to localise it," says passive house guru Tomas O'Leary, director of MosArt and founder of the Irish Passive House Academy. "In Rosslare, they decided from the very outset that they wanted a fireplace and they weren't willing to roll over and accept no for an answer. You really wouldn't know it was a passive house walking around. It's traditional and I don't mean twee by traditional- it's just got a lot of the components that Irish people like."

There are three separate forces behind this project - developer Michael Bennett, Donal Mullins of Shoalwater Timber Frame who de­signed and fabricated the thermal envelope, and low energy designer Seamus Mullins of Seamus Mullins and Co. Both Donal Mullins and Michael Bennett have been building tim­ber frame houses for the past decade, while Seamus Mullins has provided much of the de­sign know-how. He recently completed the certified passive house designer course with the Irish Passive House Academy. Throughout their working relationship, the team has grad­uated to incrementally more efficient homes. The day we met in Rosslare, Bennett was fi­nalising the sale of an A3 rated house in another of his developments in Enniscorthy.

With rising energy prices and the recession fo­cusing minds on the energy performance of their homes, Bennett believes that the time is right for this kind of development. But location is also vital- Rosslare Strand has long been a summer holidaying Mecca. "We won't have first time buyers here," says Bennett, adding that the first house in the development carries a price tag of €490,000. "We'll have I expect retiree-type clients, with maybe an odd one re­turning from overseas, but as the houses are three and four bedroom, we are also catering for families and permanent residency." Given this profile, it was always vital that the house wear its passive tag lightly. "The Irish are very slow to change," he says. "If you built a state of the art glass house, would you sell it to any­one? I don't think you'd have a hope. People would come and look at it and ooh and ahh over it but they wouldn't buy it."


Giving the house a traditional look isn't all about meeting the market's aesthetic expec­tations. Irish houses need to be designed to cope with Irish conditions. "We've higher wind-speeds than mainland Europe, it's not as cold but we've more rainfall," Seamus Mullins explains. "The moisture levels mightn't impact so much on the thermal efficiency of the house but it will impact on the quality of the build. The detailing in Europe stands up in Europe but when it's put into wind-driven rain situa­tions; suddenly you're going to start getting leaks." Moreover, the design incorporates ele­ments of Irish design that have always made sense. The draft lobby, for example, is a stan­dard feature of many of the houses in the area.

There will eventually be eight houses in Grange Lough, which is a very private wall en­closed site. "There will only ever be one house for sale here at a time," says Bennett. The de­sign and construction team have however been very careful to ensure that early arrivals won't be living on a building site. All services and preparatory work for the eight houses are in place, all footpaths and roads have been constructed, while sites due to begin later are now landscaped and will remain so until con­struction can begin. Come construction time, the houses will be built behind hoardings, and as Seamus Mullins is quick to point out, the en­hanced sound insulation of a passive house means noise is unlikely to be an issue.

The first challenge facing Seamus Mullins was achieving the right orientation for eight houses on an elongated, restricted site. "If you haven't got a front elevation facing south, you've a rear elevation facing south," he says. "So it's a matter of changing the internal room layout. Nearly all of the four designs have a central core around the stairwell that faces south." Glazing to the west had to be amended due to over­heating issues turned up by the PH PP software. The houses themselves are not large by recent standards - the designs vary between 1,860 square feet and 2,200 square feet. "They're not large," says Mullins. "That's an important aspect as well, because to comply with passive certification there's a ratio of floor area of around 35m2 per person ... That's to try and get a better use of land, money and space." When he began his timber frame business eleven years ago, Donal Mullins of Shoalwater set out to ensure that any work that could be done in the factory was done in the factory. In order to preserve quality and continuity, the team that manufacture the frames also erect them onsite. He says that when he began building timber frame houses almost thirty years ago, the first panel taken from the back of the lorry was always the last to be used, and invariably suffered from constant handling. Bearing this in mind, Mullins developed a process of packaging the building system in bales and, and loads it to ensure minimal handling. "The first panel you take off should be the first panel you use." He says.Extreme attention to detail has been the hall­mark of the build. Achieving passive certifica­tion was vital to the commercial success of the project, says Bennett. "We had to be certain of our certification before we started. Anyone starting to build a house like this without their homework done and all their planning and all their issues addressed are on a hiding to noth­ing. There's no way can you get passive certi­fication without it." To facilitate this, the house was built on paper long before a sod was turned onsite. Because of all that preparatory work, says Donal Mullins, the construction stage didn't throw up any real stumbling blocks. "I wouldn't say there were huge issues during the build," he says. "The big issues were in the learning curve itself. Because of all the work we had done previously, we had a base of knowledge to build from." All three have been continually attending seminars and conferences in order to up-skill and keep abreast of best practice.

Achieving and then keeping airtightness is of course the perennial bugbear of low energy construction. It helped in Grange Lough that no subcontractors were used, and that many of the trade’s people had been working with Bennett for more than a decade. "If you don't bring your trades people along with you, if you don't educate them, if they don't know what they're trying to do, how in the hell can they work towards it?" says Michael Bennett. "We've done a lot of work on our people here."

Responsibility for achieving airtightness in the first place fell to Shoalwater, who have won an excellent reputation for themselves in this field using the Pro Clima system of membranes, tapes and adhesives. "When we were finished, we did our first blower door test," Mullins ex­plains. "We got an air change rate of 0.51 [ACH at 50 Pa]. That was very good. Then Michael could go and say to his electrician, his plumber, this is our airtightness, this is what you have to have when you guys are done. If it goes up, it's because of something you guys did. Now they're far more conscious and far more care­ful." A blower door test after each phase not alone kept tabs on how the air change rate was being maintained relative to the passive house standard of 0.6, but also revealed who was re­sponsible if the number went up.

One key issue that arose was with the Stovax stove. The blower door test immediately fol­lowing the installation of the stove drove the air change rate above the 0.6 threshold. Re­peat visits from Stovax improved the door sealing, which is where the problem lay, and moved the rate back down to acceptable levels. Surprisingly, the unit is still not a room-sealed unit. Though most of the air required from combustion is piped in externally, a small pro­portion is still taken from room air.

A potential issue also arose with the Beam cen­tral vacuuming unit. Though bin and turbine are both located within the sealed envelope, air could theoretically have escaped through an extract pipe which terminates outside the house. "We could have had a problem there," says Seamus Mullins, "but we were never going to find out if we didn't put it in. From a clean­ness and dust elimination point of view, the central vacuuming system is superb. The filtering system really fits with the passive principle in that you're creating this quality comfortable living environment." The solution which Beam came up with was a motorised valve, kept shut while the unit is not in operation, and triggered to open when switched on. The blower door test however u

ncovered no leakages in the system so the valve was not fitted.

The windows are from Munster Joinery's Fu­ture Proof range. "Passive house windows gen­erally cost people about €650 a square metre:' says Brendan Harte of the company.”We wanted to bring the price down, we wanted to put value for money into the market but still achieve the passive house standard. The glass section is 52mm triple-glazed and the PVC pro­file that we went with in Rosslare is a 90mm section, fully foam-filled all the way through." Two Munster Joinery windows are currently with the Passive House Institute in Darmstadt undergoing certification. The Passive House In­stitute was heavily consulted during research and development of the window range to en­sure that the onerous certification requirements would be met. The windows are the first Irish products submitted to the institute for certifi­cation. "I think that's very exciting because windows typically are the most expensive ele­ment in the passive house:' says Tomas O'Leary.”They're often imported and I think in these times, if we can generate local employment in construction, that's better for everyone."


"People are amazed when they hear that the windows are Irish, says Seamus Mullins.”Peo­ple think we should have Austrian or maybe German windows, we shouldn't have Irish win­dows, and are surprised to hear of the product range advancements that Munster Joinery have made." But using local products isn't just about local pride, says Donal Mullins. ''That window is a brilliant window and we can get it in Ire­land in a two week delivery date. It's so much easier to run a schedule when your window manufacturer can have them in ten days to two weeks, at this quality and with an Irish fit­ter. You've got any kind of little latch or lock problems, you ring him up and the serviceman is here." One of the most interesting findings of the project was in relation to cost. Seamus Mullins tracked expenditure throughout, and pre­sented a paper at the SEAl See the Light con­ference in Croke Park last September. He found that the cost of upgrading a project from A3 to passive came in at 02 per square foot. "That's in our first attempt:' he says.”We should be able to pull that down." The Grange Lough house is currently awaiting confirmation of its BER, which Seamus has calculated at high A3. He refers to Bennett's A3 house, just sold in Enniscorthy. "The funny thing is both the pas­sive house and the Enniscorthy house are A­-rated. In Rosslare, the running costs for all your heating and hot water, are going to be in the region of €500 - €600 a year, on the basis of an energy demand of 10 kWh/m'/a, while in En­niscorthy, the A3 rated houses is going to have an energy requirement of 67 kWh/m'/a - which is approximately six times more. It might not be six times more expensive to heat, but if it's three times more expensive, that means the Enniscorthy purchaser is spending an extra 0,500 to 0,800 a year for the life of that house."In order to meet the passive house standard, the house must be designed to have an annual heating demand of not more than 15 kWh/m'/yr. In Rosslare, the calculations are coming in at 10 kWh/m'/yr, 33% below the standard. Michael Bennett explains that they needed to aim high in order to provide sufficient comfort to ensure that certification would be achieved. "But we're going to get better at this, and more efficient at it:' he says. Being the first passive house in the scheme, everyone involved in­vested a huge amount of time and effort in achieving the right results. Bennett sees this time as an investment in skills and experience, and believes that from here on in, each house will go up within three months.

These houses are finished with the high end of the market in mind, but Bennett believes that it's entirely possible to provide the same qual­ity of build for the lower end. "I would hope, if not this year then in two or three years down the road we'll be starting a small scheme some­where. Ten or twelve houses, and they'll be 'white deal passive', to give passive certified houses to entry level buyers." Donal Mullins agrees. "Why not get into a position where we can supply passive houses at affordable prices to the county councils?"

Does Passive House Require a New Design Language?

Architect Paul McAlister

Architect Paul McAlister

The movement of building standards towards passive house and rising fuel prices are the main initiatives driving the construction industry in the direction of certified passive house standard within Northern Ireland. It is an attractive aspiration for us within the construction and design industry to be at the forefront of low carbon design and passive house design in Northern Ireland, whilst making positive contributions to C02 emissions. Fully pursuing this standard within this industry would also open up export markets for our knowledge, skills and products, however in any potential advance towards an implementation of passive house there are many issues to be considered. The first issue is the capital cost of a passive house build. It is not possible to put a figure on the extra cost for a passive house building over a conventional building which barely complies with the 2008 Building Regulations. This would be far too simplistic. Cost depends on a whole host of variables, which includes the private residential sector, passive house clients generally insist on high quality fixtures and fittings. For example, the extra cost for passive house standard windows over standard triple glazed windows, may be due to improved functionality alongside achieving the energy standard and the criteria of passive house certification.

Those taking up the challenge and aspiring to build to passive house standard should have a clear idea of the budget limitations surrounding their project and the space requirements that budget will deliver. However, many designs, despite the best efforts to optimise design and energy modelling, will always fall short of certification. Often additional improvements which move the design towards certification don’t quite make the passive house threshold for space heating demand of 15kWh/m2/yr. Having a heat demand slightly higher than the threshold, at say 18kWh/m2/yr may have slightly higher running costs, but they are minimal when compared with capital costs of finding the final 3-5kWh in some cases. Each individual project must weigh up their capital expenditure versus running costs to decide what is best for them. When the site condi­tions and design strategy produce a performance for heat demand that falls inside the passive house criteria then certification becomes a simpler process. However if the threshold is missed by a few kilowatt hours, resulting in the design being un­able to deliver the space heating solely through the ventilation system, it may be better suited to add a secondary heat source whilst still achieving a high performance building. With unusually cooler winters predicted for the coming decade, having some extra, user-controlled, heat contributors such as the addition of a couple of radiators may be beneficial.

Another issue of the application of passive house is design, which by its nature is subjective to the client and architect. A number of bespoke, architect-designed homes are being certified within Northern Ireland, which is a promising sight. However it is difficult to imagine standard ‘off the shelf’ designs being replaced with homes designed to optimise site and energy performance. Passive house can be adapted to every conceivable style of building with the emphasis placed by the passive house modelling tool on efficient building envelopes and internal layout and orientation. This could place added expense on those restricted to single storey buildings by planning. The proposition as to whether or not ultra-low energy buildings will require a new design language and how they will contribute to urban and rural landscapes is an unknown factor. It is important that planners are educated to recognise this new typology of building that may deviate in form from designs favoured today for example, by having a design that does not necessarily face the road.

The regulatory compliance, concerned with the recognition of passive house can be an issue. The two equivalent energy performance methodologies within building regulations have shared objectives to considerably reduce energy use, but actually have conflicting methods. Passive house comes with a difficult certification process, requiring air leakage testing after completion and evidence of installed insulation. It provides a model for inspection of low energy builds to ensure that adequate attention to detail is applied. Passive house prioritises minimisation of heat loss above all else, while the SAP methodology for Part F compli­ance is not as strict on fabric and ventilation heat loss but puts a high emphasis on the use of renewables. The English version of Part L 2011 came into effect in October 2010 with enhanced standards of performance required. A proposed solution to these conflicting methodologies is that the passive house standard could be recog­nised as an alternative method of compliance with the new Part L. This could provide a pos­sible strategic move by government to support the potential of the pas­sive house building sector by moving building regulation in line with the requirement of passive house certification.

The final issue concerns knowledge of pas­sive house building procedure. There is an education process needed to show how passive house standard buildings and its retrofit equivalent EnerPHit are achieved. The responsibility of propagating this information needs to be taken up by our enthusiastic designers and architects. It would be desirable if funding for research of new, more cost-effec­tive materials and technologies is secured and buildings already complete and in use at this standard should be monitored.

The point where every new building and renovation is a certified passive house may never become a reality, however it is not the attainment of certification that's important but the aspiration to go as far as is practical within the limitations of each project. It is therefore vital to accept no less than ultra low energy buildings in an attempt to make our entire building stock practically passive house standard; this would put into practice now what building regulations will eventually catch up with in the future.

Paul McAlister

Taking Control Of Air tightness

According to the Energy Saving Trust's Chief Executive Philip Sellwood, almost a third of new homes are still failing to meet energy efficiency guidelines. He told the BBC " ... the Government's 'Code for Sustainable Homes' is not being adequately enforced, giving cause for real concern. Our building regulations in the UK are among some of the toughest in Europe, but they are extremely poorly enforced as far as energy efficiency goes".

David Arendell, MD of roof ventilation specialist Klober feels the situation in respect of building air tightness gives grounds for even greater concern. He commented, "In the light of the EST's comments on energy efficiency, it is fair to assume that the level of understanding of how best to achieve air tight construction remains poor.

This is despite the fact that the phrase 'Build tight, ventilate right' has become synonymous with the strategy to achieve low energy buildings. If we don't understand how best to achieve the right balance of air tightness and controlled ventilation, we run the risk of perpetuating condensation problems within the roof space and building fabric. With every upgrade in insulation standards, so the risk increases.

Delays in consultation on Approved Documents Land G have prompted deferment in CSH 2010 until the end of the year, but the clock is undoubtedly ticking towards an ultimate target whereby all new homes achieve CSH Level 6 (effectively zero carbon). However, with house builders having lobbied consistently for tighter definition of how 'zero carbon' can be achieved, the Zero Carbon Task Group was set up.

There is some evidence to support such calls for redefinition. Research carried out in 2007 by the Richard Hodkinson Consultancy, for example, showed that 'PassivHaus' (a Europe-wide Standard with stringent air tightness requirements managed by the BRE and the Energy Saving Trust) would not actually meet CSH 3.

CSH assessment uses the Standard Assessment Procedure (SAP) test to calculate energy performance, and for a number of years there have been questions over the efficacy of the test, especially in relation to more thermally efficient buildings.

In terms of roof design, the requirement already exists for new public sector housing to meet CSH 3. The impetus towards 'zero carbon' will be reinforced when the equivalent of CSH 3 is incorporated into Building Regulations for England and Wales (some authorities indeed have already adopted this requirement). In Scotland, where many elements of the Code have already been incorporated into Building Standards, similar improvements are planned.

Of the nine categories within the CSH method of assessment, that for 'energy and C02 emissions' is by far the most significant. This is true for both the allocation of credits within each category and the final point’s allocations that result from use of weighting factors. 29 credits are available for energy and C02 emissions which, when weighted contributes 36.4% to the total available performance.

The right balance between air tightness and ventilation can certainly be struck without significant addition to building costs. Material choice however, can greatly influence a building's long-term air tightness. Sheet membrane air barriers coupled with sealants, for example, are more effective than sealants alone, counteracting the effects of buildings (particularly timber frame) drying out.

Housing designers can now benefit from Accredited Construction Details (ACDs), Enhanced Construction details (ECDs) and, in Scotland, the Scottish Ecological Design Association Guide for both warm and cold roof construction. Examples of wall/ceiling ACDs include a junction of ceiling level air barrier with masonry inner leaf and warm roof with room in the roof. Accredited detail Sheet MCI RE 02, for example, shows a warm roof detail at the eaves in a non-habitable loft using Klober Permo forte vapor permeable underlay and appropriate tapes (with an alternative pre-taped option).

For non-residential construction, air tightness is just as important, despite the absence of any CSH equivalent. Roofing materials such as zinc, for example, require airtight construction if the metal's underside is unventilated. At the recently build Abergwynfi primary school near Neath, built to achieve a BREEAM 'Excellent' rating, zinc was used on a series of circular roofs. A Klober Wallint air barrier was installed with sealing tape to meet the specified air tightness performance.

With current Building Regulation requirements stipulating air tightness of only 7m3/hr per m2 compared with CSH 3 at 3m3, techniques used to achieve it must undoubtedly change. CPD presentations and literature on the subject are to be welcomed. 'The Code for sustainable Homes and air tightness in roofs' is a CPD presentation from Klober examining how to 'build tight and ventilate right' within the realms of practical pitched roofing construction. Supported by ‘Taking control of air leakage' tightness it is a welcome source of information on a subject for which information is otherwise lacking.

By David Arendell, MD of Klober

The Low Carbon Buildings Programme - Energy Saving Trust

If you are a householder in Northern Ireland interested in generating your own heat or electricity, you can apply for a renewable technology grant of up to £2,500 per property. The Low Carbon Buildings Programme incentivises householders interested in fitting their own green energy systems, such as solar photovoltaic’s, wind turbines, small hydro, solar thermal water, ground source heat pumps and Bio energy, by providing grants to contribute towards the cost of installation.

The Programme is funded by the Department of Energy and Climate Change and managed by the Energy Saving Trust. Many people claim that they want to do their bit to help tackle climate change but are put off by the costs associated with renewable technology. By taking advantage of the grants available through the Low Carbon Buildings Programme, homeowners will find small renewable technologies a more affordable option. By installing micro generation technologies, homeowners will not only play a vital role in tackling climate change but will also save themselves money in the long run.

Noel Williams, Head of the Energy Saving Trust Northern Ireland commented: "I am pleased that householders in Northern Ireland have already applied for grants to install green energy technologies through the Low Carbon Buildings Programme and hope that even more people will follow in their footsteps and reduce their carbon footprint."

To be eligible for a grant through the Low Carbon Buildings Programme, consumers must choose a certified product and have it installed by a certified installer.

What is a Passive House?

A Passive house is a building in which indoor air temperatures of a minimum of 18°C are maintained year round without the need for heating appliances.

That’s right, you don't need neither radiators nor wood or gas burners nor air conditioners to live in a comfortable, dry and well ventilated house. This isn't a case of wishful thinking but rather of applied physics. All you need is a maximum heat load of 10W/m². Each new building can be a Passive House.

Is this an experimental concept?

No. There are currently more than 8,000 Passive House buildings operating in Europe (most of them functioning under more extreme temperatures, than you will find in Ireland), the oldest one of them up and running since 1991. The Passive House concept is proven both scientifically and practically to work well.

Is a Passive House also a Zero Energy House?

No, it is not. You still need a minimal amount of external energy to provide a comfortable and healthy indoor climate in a Passive House, although in some regions in Europe that amount would be next to zero. You certainly can go the extra mile, and turn a Passive House into a Zero Energy House. But this very last part of the process is the most expensive. A Passive House tries to balance economy and ecology, and therefore stops short of the last measures. You can easily cover the remaining need for heating and cooling energy with renewables, though, but the applied technology can be expensive.

Why is it called Passive House?

A Passive House tries to provide a comfortable and healthy indoor climate without the need to use active heating or cooling appliances. It heats and cools itself. There are machines to facilitate this purpose, namely an efficient ventilation system (not air-conditioner!), but I consider a fresh air ventilation system a vital ingredient of a healthy and comfortable home anyway. A good ventilation system with efficient heat recovery will actually save energy.

Do I need to have a South facing site to build a Passive House?

No, there are plenty of examples where a Passive House works perfectly without being aligned to the south. It’s a bit harder though, but definitely possible.

Do I need thermal mass?

No. Thermal mass is a helps in the retention of solar energy. Nice to have, but not unchangeable.

Can I open the windows in a Passive House?

Sure you can! Only – you don’t need to do it anymore. But you definitely can do it, if you want. That’s freedom of choice, isn’t it?

Are there specific shapes needed for a Passive House?

No. You might very well build a Passive House that looks like a 19th century villa. You can have it look traditional or modern. They come in all sizes, too.

What about summer?

The good news: insulation works both ways on opaque components like walls and roof. The “solar” design you chose to catch the sun in winter however could be a mayor problem in summer. One more reason why you shouldn’t watch window sizes, because thereby you also magnify solar gain. But there is a solution: keep the sun out in summer simply by using movable shades, like shutters. Always put them on the outside of your windows. It would be nice to automate closing and opening in dependence of solar radiation, too. That could be done quite easily with a small photovoltaic sensor and solar driven motor.

The ventilation system can, in combination with a mostly passive ground heat exchanger, work as a dehumidifier and also cool down indoor air a bit. Again: a big step towards comfort with only a small amount of energy!

How does it work?

It works by minimizing heat losses and maximizing passive heat gains. To minimize heat losses you first and foremost need lots of insulation. By insulation I mean materials with a thermal conductivity ≤ 0,1 W/(m K). This could be glasswool, polystyrene, foam glass, fibreboards, straw bales or others – in a word: low density materials with many enclosed air cavities. Neither rammed earth, nor clay, nor loam, nor concrete would do, since all of those don’t have noteworthy insulation values. All the windows, too, need to be very good insulated. And don’t exaggerate window size.

Think of your home as a present: you need to wrap it all around neatly. And don’t forget the corners!

Next you need an airtight barrier interior of the insulation layer. That could be made of any material that is and stays airtight. Building papers, polyethylene foil, plaster etc.. Just don’t forget joints and connections. They need to be airtight, too.

You need to ventilate your home. But you don’t need to loose indoor warmth doing it. Heat recovery is the solution. It only works well in airtight houses, though.

Now that you’ve cut the losses, maximize the gains. Catch as much winter sun as possible – but avoid overheating at the same time. Try to align the house as south facing as you can, and provide shades on the outside of the building.

You also receive gains from appliances and occupants. But it isn’t very wise to maximize gains here. In the case of appliances: you wouldn’t want to waste the energy you save on heating to run inefficient appliances (inefficient appliances only generate minimum heat). Heating problems solved, think about warm water supply. You can easily get it without burning fossil fuel or fossil generated electricity. Solar water panels are readily available to do the job without sending monthly bills. Solar panels may be integrated into the heat recovery system. Even a clothes dryer can be part of the ensemble. It is very well possible to build a Passive House in Ireland!

A Passive house, what’s in a name ?

The term Passive house comes from Swedish and German research into creating low energy houses, in terms of running costs. The concept was taken further in Germany with actual working models constructed that became known as Passivhaus or Passive House. The Passivhaus Standard is a holistic view of how a house may be constructed with the primary aim being energy efficient living. The Passivhaus Institut in Germany has set criteria for achieving the Passivhaus standard which, in effect, calculates the dwellings energy consumption.     The key to linking the name ‘Passive’ with the function of the building is to remember that the house is Passive in terms of its impact on the environment and its active energy requirement. To achieve this, these houses must incorporate features that other houses do not have at present.

This Passive House technology is now readily available, but is often poorly understood. It is also perceived as much more expensive to implement. The additional cost figures vary at between 10-15% more expensive that conventional building to the current building regulations. When taking a view as to the extra cost of achieving Passive standards it must be remembered that the energy saving year on year will pay-back the difference in of 5-10 years, after which time the dwelling is saving the occupants money. This future proofing of the house, in terms of energy use means that the houses inherent value would be maintained over the future years.

How do we achieve a Passive house? It is an area that needs professional advice and a ‘whole house’ approach as there are a number of permutations in achieving the standard.  The technology is also advancing making the choice of materials and technology reliant on the latest market innovations.

In order to put a marker down we have itemised the main principles and elements to make a passive house function. These ‘Passive house’ standards  are intended for the  European climate and would not be suitable for more extreme climates.

Characteristics of a Passive house

A ‘whole house’ approach is needed to the design a passive house.  The technology available to achieve the considerable energy efficiencies is advancing, making the choice of materials and technology reliant on the latest innovations in the market. The skill of the designer is to best employ the available materials and systems to achieve this low energy standard.  

The ‘Passive house’ must have all of the following features to function in the typical European climate.

Super Insulation and elimination of cold bridges

The most important aspect of low energy housing is the most simple to comprehend. It is a super-insulated envelope ( walls, floors, roof, windows and doors ) to the dwelling. It requires very high levels of insulation and special detailing of openings and junctions to ensure there are no ‘cold bridges’ to allow for the transmittance of heat through the building fabric. The windows for a passive house also have to have exceptional insulation standards in keeping with the other elements. It is often a misconception that the employment of renewable energies will produce a passive or low energy house but without the fundamental insulation element the use of renewable energy technology can be wasted.

Air-tightness of building fabric

In conventional houses up to 20% of energy may be lost through air infiltration or drafts that occur commonly at junctions of floors, doors and windows. For this reason passive houses are extremely well sealed in terms of air-tightness and this aids retention of heat. In current building an air pressure test is carried out on new dwellings. The building regulations are relatively easy to obtain, in terms of workmanship. The passive house standard is more onerous and relies on more careful consideration and detailing of the building fabric. Good on site construction techniques and supervision is recommended.

Circulation of fresh air

The need for active ventilation to passive houses is recognised due to the air tightness and this requirement has been developed as an advantage. A mechanical ventilation system is employed to maintain air quality. The rate of air change can be optimised and carefully controlled at about 0.4 air changes per hour. Passive houses have active ventilation to all rooms in the dwelling. The air in rooms that produce active heat, and odours, such as kitchen, bathrooms and utility room is extracted. Rooms that require heating such as bedrooms and living spaces have fresh air vented to them.  Overall the balance of air is maintained within the house by air movement below internal doors and an open plan house. The reason for this ventilation is to provide fresh air to the house and to avoid the build up of water vapour or condensation in the house due to the air-tightness. It should also be remembered that at any time a window can be opened for additional ventilation although in winter opening a window for ventilation would cause heat loss.

Heat recovery from circulated air.

The circulation of air is handled with mechanical ventilation which has the crucial element of heat recovery, commonly known as MVHR ( mechanical ventilation with heat recovery). The clever aspect of the system is that it literally ‘transfers’ heat from the extracted stale air to the incoming fresh air (which is ducted from the outside). The efficiency of heat transfer is over 85% and the majority of the heat from extracted air is therefore not lost to the building envelope, as with conventional extraction.  The system of heat transference to the cold incoming air means that the houses environment may be regulated and maintained at a higher temperature, for most of the time, without the need for an additional energy source except the low running cost of the MVHR. This system is often the least understood in terms of convincing the public of the benefits of passive houses and perhaps most off-putting to the public. Negative images of ‘air conditioning’ units humming on the ceiling are brought to mind. In fact this is not ‘air conditioning’ of the conventional type. The MVHR runs on less energy needed for a 100 watt light bulb and functions continuously, the unit may be located in utility rooms and have health benefits in that the air is filtered before entering the house. A significant amount of heat is produced with common domestic processes such as cooking, showering and the use of various electrical appliances.  Human bodies give off a significant amount of heat (People, on average, emit heat energy equivalent to 100 Watts) and this is significant to a passive house as the energy loss through the fabric of the building is so low. )To put this in perspective a 100 watt light bulb should be capable of maintaining the space heating of a 10 metres square room. Two 100 watt light bulbs would therefore have the capability of heating to a higher temperature the same room.)

Ventilation system used for active space heating.

The MVHR system is required to maintain air quality. The MVHR also acts as ‘air source’ space heating for the house in that the heat recovered from extracted air is transferred to incoming air and circulated throughout the house. This benefit along with a super-insulated envelope means that passive houses are able to dispense with conventional heating system as they would quickly overheat the building. Some additional source of heating is recommended as this would be required when the house is not occupied (no passive heat is generated ) or in severe weather conditions. Most Passive buildings do include a system to provide supplemental space heating. This may be distributed through the low-volume ( MVHR ) mechanical ventilation system. One recommendation is to have a dual purpose electrically operated 800 to 1,500 Watt heating and/or cooling element integrated with the fresh air supply duct of the heat exchanger ventilation system. It is important that the (MVHR) ducting is adequately sized to allow for this element of active space heating and the volume of air required for space heating ventilation.

Energy source for active space heating to the passive house.

The air-heating element associated with the fresh air intake air to the MVHR units can be heated by a small heat pump, by direct solar thermal energy, or simply by a natural gas or oil burner. In some cases a micro-heat pump is used to extract additional heat from the exhaust ventilation air, using it to heat either the incoming air or the hot water storage tank.

In some instances small wood-burning stoves can also be used in space heating and the water tank. Care is required to ensure that the room in which the stove is located does not overheat. The ventilation system would also need to be configured to circulate this hot air around a house that may not be open-plan.

Triple glazed high specification windows

A requirement of the super-insulation of passive houses is that the windows frame and glazing must be of a suitable insulation quality to stop excessive heat loss. Conventional double glazed windows are unable to meet the thermal values required and for this reason triple glazing is required along with specially designed window frames, with thermal breaks, that have a low thermal conductivity. It should be noted that the window glass may be coated and an insulating gas used in the sealed system to achieve the desired values.

Passive solar gain / orientation

One last feature of passive houses is the orientation of living spaces in terms of making use of solar gain. The capture of passive solar energy by glazing within the fabric of the building may be used to heat the Thermal mass of the building during the day and this heat is then released or radiated during the night stabilising the temperature of the house. The use of concrete floors to act as a thermal store for the suns heat during the day is a simple way of retaining heat and for this reason the glazing to the south may be sized to take advantage of this. The passive houses we are designing are not ‘Passive Solar Houses’ and overheating due to thermal gain can be a problem in sunnier climates and potentially lead to overheating of Passive houses.

Some characteristics of Passive Houses

The air is fresh, and very clean. Note that for the parameters tested, and provided the filters are maintained, quality air is provided. 0.3 air changes per hour are recommended, otherwise the air can become "stale" (excess CO2, flushing of indoor air pollutants) and any greater, excessively dry (less than 40% humidity). The use of a mechanical venting system also implies higher positive ion values. This can be counteracted somewhat via opening the window for a very brief time, plants and indoor fountains. However, it should be noted that failure to exchange air with the outside during occupied periods is not advisable.

Inside temperature is homogeneous; it is impossible to have single rooms (e.g. the sleeping rooms) at a different temperature from the rest of the house. Bedroom windows can be opened slightly to alleviate this when necessary.

The temperature changes only very slowly - with ventilation and heating systems switched off, a passive house typically loses less than 0.5 °C (1 °F) per day (in winter), stabilising at around 15 °C (59 °F) in the central European climate.

Opening windows or doors for a short time has only a very limited effect; after the windows are closed, the air very quickly returns to the "normal" temperature.

The air inside Passive Houses, due to the lack of ventilating cold air, can be drier than in 'Standard' Houses. This may be counteracted by slowing the rate of ventilation to allow water vapour to build up within the house as required to comfort levels.

Appendix 1.   Technical energy targets for passive house in Western Europe Climate.

The Passive House standard for central Europe requires that the building fulfils the following requirement,

The building must not use more than 15 kWh/m² per year heating and cooling energy.

 Total energy consumption (energy for heating, hot water and electricity) must not be more than 42 kWh/m² per year

Total primary energy (source energy for electricity and etc.) consumption (primary energy for heating, hot water and electricity) must not be more than 120 kWh/m² per year


 With the building de-pressurised to 50 Pa (N/m²) below atmospheric pressure by a blower door, the building must not leak more air than 0.6 times the house volume per hour (n50 = 0.6 / hour).

 Further, the specific heat load for the heating source at design temperature is recommended, but not required, to be less than 10 W/m².