Passivhaus FAQs

Passivhaus design is suitable for everyone – residential and commercial – but there is a lot of misleading information. We provide the answers to some common misconceptions.

“Passivhaus is a German standard so isn’t appropriate for the UK.”

Whilst it is true that the Passivhaus standard was developed originally in Germany by Professors .Wolfgang Feist and Bo Adamson, each Passivhaus design is based on the use of local climate data and is therefore fine-tuned to suit the particular region in which it is being developed. Passivhaus has been shown to work from Qatar to Canada, from Korea to New Zealand. The Passivhaus target is universal; the solutions are local.

“Isn’t Passivhaus just the latest sustainability fad? There’ll be something else along soon!”

The first Passivhaus was completed in 1991 in Darmstadt and has been occupied ever since – 25 years of consistent performance. There are thought to be over 20,000 Passivhaus buildings in the world and hundreds in the UK. Passivhaus is not a gimmick or a fad or a system … it is a scientifically-based component of building design and a quality assurance standard. It has been so successful in delivering low energy buildings that perform as intended that it has been adopted as the mandatory building standard in cities such as Brussels, Frankfurt and Dun Laoghaire-Rathdown County in Ireland. Outside of its north European heartland, Passivhaus is also taking off in the USA, Australia, Japan, Turkey and China – it’s safe to say Passivhaus is here for the long term.

“I like to open windows, I can’t live in a sealed box!”

And nor should you have to with a Passivhaus! All Passivhaus buildings have windows that open, not least for easy cleaning, and this may be of particular importance in the summer as part of a night cooling strategy. But what about when the weather outside is not conducive to opening windows, because of windy conditions or heavy rain perhaps? Or what if the building is situated in a noisy urban environment? It is just as important to maintain good air quality under these circumstances. Good ventilation and air quality are central to the Passivhaus concept, with filtered, fresh air being supplied, slowly and quietly, to all habitable rooms to balance against stale, moist air extracted from kitchens and bathrooms. By controlling the level of air leakage through the building envelope, it is viable to recover the heat energy from the exhaust air – so the more air tight the walls, floors and ceilings, the more efficient the ventilation system’s performance for the minimum of fan energy use. Counter-intuitively, Passivhaus owners have found that they can have the windows open more often because the heating season is so much shorter and the lack of draughts and warm interior make it comfortable to do so!

“Passivhaus is just expensive compared to other types of eco houses.”

This very much depends on a client’s priorities. Complexity usually increases costs because of the additional materials, structure and technologies – Passivhaus on the other hand encourages simplicity and practical construction so, if the design principles are built in from the outset, it doesn’t have to cost significantly more at all. Passivhaus does involves the use of high performance components such as super-insulation, windows and heat recovery ventilation that ordinary buildings might not incorporate so these individual elements may cost more. But when there are such significant savings to be made long term in energy costs, they amount to a sound investment.

And if you choose Cowan Eco Design as your architect, you won’t need to employ a separate Passivhaus consultant!

“I want a Passivhaus but without the architectural restrictions . . .”

Passivhaus is a design and quality approach to building, not a fixed solution. It will be down to your design team to marry architectural ambitions with Passivhaus principles, in much the same way as any building needs to comply with means of escape or structural regulations. Increasingly, the building industry provides solutions that permit more expressive architecture without having to compromise on energy use. Check out the winning buildings in the International Passivhaus Association 2014, for which Cowan Eco Design’s Mark Elton was a jury member, to see the diversity of design that is possible.

“I don’t want heat recovery ventilation . . . it’s just too noisy and it can’t be healthy!”

On the contrary, heat recovery ventilation that has been designed and installed in accordance with the Passivhaus standard should be practically inaudible and significantly improves indoor air quality. This is because it incorporates filters that cut out dust, particles, pollen etc and is designed to include acoustic silencers between rooms and sound proofing to the main heat exchanger. Only rigid metal or semi-rigid plastic ducts are used to cut out vibration noise. Many residents moving into a Passivhaus home have found that their respiratory problems have improved thanks to the better indoor air quality. And since in a Passivhaus the wall temperatures are designed never to drop below 17 degrees, condensation and mould can never form – another health reason to choose Passivhaus.

“I read that Passivhaus homes overheat in the summer?”

Any house that is well insulated for winter conditions has the potential to overheat if poorly designed and abused in operation. Passivhaus certification is very focused on this issue and designers have to demonstrate, using the bespoke software, that overheating risk has been mitigated through a shading strategy, a night ventilation strategy or through use of coolth recovery from the ventilation system. UK experience from existing Passivhaus buildings shows that if the building is not over-glazed, as many ‘passive solar’ buildings are, and internal heat gains are managed sensibly (by insulating the hot water system well, for example) then a Passivhaus stays cool in summer. After all, insulation keeps heat out as well as in, just like your fridge!

“I really want a home that is holistically eco-friendly and Passivhaus doesn’t cover that.”

Passivhaus is targeted at energy use because that has the biggest environmental impact but you can of course choose to build a Passivhaus from eco-friendly, natural materials. Timber, wood fibre, wool, clay, recycled newspaper pulp and even straw have all been used in the UK for Passivhaus projects. Cowan Eco Design can help with the selection of the most environmentally benign materials for your Passivhaus.

“I’ve just bought a property for refurbishment, rather than build new, so it’s too late to think about Passivhaus for me.”

Passivhaus is typically achieved through careful planning of the building form and orientation, window sizes and positioning with close attention to detail in the construction methodology to avoid thermal bridges. In refurbishment projects, many of these factors are pre-determined by the existing building. Nevertheless, a Passivhaus retrofit standard has been developed, known as EnerPhit. It incorporates the same scientifically sound principles, comfort and quality standards but allows some relaxation on the energy and air tightness targets to reflect the additional difficulty of compliance. Cowan Eco Design Director, Mark Elton, has experience in designing to the EnerPhit retrofit standard – for more information refer to our lasting retrofit download info sheet.

“My project isn’t residential so I don’t think Passivhaus is an option and I’m not considering it.”

The first Passivhaus in the UK was actually a community centre and there are many other types of buildings now certified including university buildings, schools, care homes, offices and even an archive. Across the world buildings as diverse as museums, prisons, supermarkets and swimming pools have been certified as meeting the standard.

“I want a building that is self-sufficient and generates it’s own energy needs so a passive building doesn’t go far enough for me.”

Many Passivhaus buildings incorporate solar water heating or photovoltaics in the design and thanks to the Passivhaus design philosophy the amount of energy needed to be net self-sufficient is greatly reduced. The latest Passivhaus software introduces the Passivhaus Plus standard which accounts for exactly this requirement.

For a PDF download of these FAQs, click here.