Passivhaus – your questions answered

Passivhaus is a design methodology which maximises the health and comfort of buildings while massively reducing their energy consumption.

The Passivhaus approach is not dissimilar to standard approaches to low energy building design but it takes core principles such as insulation, draught proofing and double glazing much further. Passivhaus buildings have an optimal combination of added insulation, lack of draughts and air leakage, advanced glazing as well as a mechanical ventilation and heat recovery system (MVHR), which provides up to 80 percent of heating needs through warmed fresh air. This results in buildings which stay comfortable “passively” for most of the year without the need for large and costly heating systems.

Such is the success of Passivhaus that it’s almost a ‘design movement’ now. Since the first Passivhaus was built in Germany in 1990 there are now more than 7,000 Passivhaus buildings across Europe, with further projects planned across the globe including South Korea, the US and New Zealand. Refurbishment projects, schools, offices, sports centres and fire stations have all been built to the standard.

Why has it been such a success?
Its success lies in its simplicity. A building is deemed to meet Passivhaus standards provided it has a space heating demand below 15kWh/m2/ year and primary energy does not exceed 120KWh/m2/year.

These targets are verified with a comprehensive and accurate energy design tool (the Passivhaus Planning Package), which results in highly efficient buildings that require little or no energy use for heating or cooling, very low energy bills overall as well as excellent internal comfort and indoor air quality.

In what ways do Passivhaus standards for schools or offices differ from housing?
Commercial buildings and schools will follow the same energy model (PHPP) and techniques as housing but the occupancy inputs will obviously be different. As a result, the design priorities differ, but the space heating and cooling target of 15kWh/m2/year remains the same. The primary energy target of 120kWh/m2/year is a good starting point, but in practice some schools and offices are achieving this already. Therefore, on projects we are currently working on, we are aiming for even lower.

At Inbuilt we are also particularly interested in the options for Passivhaus care homes – ultra low energy accommodation for elderly and vulnerable people which also gives them a really healthy and comfortable environment without eating into the pension.

Sounds like the answer to all our sustainability needs! Is there anything else that needs to be done?
Sadly, yes! We’re a long way from realising a sustainable society. Sustainability is about much more than zero carbon or environmental wizardry, it’s also about making people’s lives better, now and in the future. Even Passivhaus buildings can overheat in summer or suffer from bad acoustics if poorly designed. If occupants are uncomfortable in their surroundings, we can’t call this sustainability.

At Inbuilt we commonly use Passivhaus as a starting point for sustainable buildings, but we also use other tools to deliver the full health, comfort and sustainability outcomes.

Can any architect design a Passivhaus building?
I think all architects should have a go, as long as they don’t underestimate how challenging it is.

While only a small group of architects in the UK currently have the in-depth knowledge and level of understanding to deliver buildings to Passivhaus standard, interest is growing all the time. Passivhaus is something that has to be planned from the very start of the project, not ‘bolted on’ half way through a project’s design. Ideally the architect will be trained to use the Passivhaus Planning Package, and will understand how to design for genuine sustainability.

I’d also strongly recommend getting a German speaker on-hand – most of the in-depth knowledge and experience on Passivhaus is written in German so a lot of important lessons get lost in translation if you can’t access this information. I’ve learnt this the hard way struggling with online translation. Thankfully Inbuilt now has three German speakers!

Can I design a Passivhaus building in masonry, or is it easier to meet the standards if I stick to timber frame?
There are examples of masonry, steel, timber, even straw bale Passivhaus buildings. Providing you have the right thermal and air tightness detailing, any kind of construction is suitable. However, in terms of air tightness, it’s often easiest to control workmanship on prefabricated systems.

I’ve heard that you can’t open windows in a Passivhaus building – is that true?
No! Windows can be opened in Passivhaus buildings. But in practice most people choose to keep them closed in the winter as continuous fresh air is provided by very quiet mechanical ventilation systems. Comfort levels are very high and air quality is exceptionally good which is great news for any asthma or allergy sufferers.

Do Passivhaus buildings need a heating system?
Passivhaus buildings don’t usually have a traditional central heating system. Instead they have a smaller, lower cost heating system which can meet the reduced heat demand.

Do we have the construction or site supervision skills in this country to achieve Passivhaus standards?
There are pockets of expertise starting to develop in the UK but the quality of construction required in Passivhaus is new to many builders. The UK is also learning from leading countries such as Germany and Austria, which have a long experience of Passivhaus. Over there, contractors and architects tend to work in partnership to deliver a number of Passivhaus projects, learning through experience until Passivhaus becomes second nature.

Is there a reliable supply chain in the UK, or do I need to import building materials and systems to meet Passivhaus standards?
At the moment, the supply chain is mostly from Germany and Austria and some international companies working across the EU. But at Inbuilt we are increasingly talking to UK-based manufacturers of doors, windows, boilers and other equipment to teach them about Passivhaus and encourage them to manufacture products which are of the correct standard.

Why are there no certificated Passivhaus buildings in the UK? What puts people off getting an official certificate authenticating the building’s performance?
In the UK there are a few good examples of Passivhaus design principles in action, but no certified buildings as yet. Several schemes are in planning, and a few of Inbuilts projects will be coming to site this year.

Inbuilt can provide certification in collaboration with the Passivhaus Institute in Germany. The process involves a check of the Passivhaus Planning Package inputs (the energy model with which a Passivhaus is designed), documentation of the build process and, importantly, an air pressure test.

Why is there such interest in Passivhaus buildings in the UK now?
Building professionals in the UK are starting to take notice of the many advantages of Passivhaus, in particular the minimal energy bills which are associated with it. In a political and business climate where sustainability is so high on the agenda, Passivhaus is definitely the way forward.

Also the Passivhaus community in Europe is a very open one, willing to share information and knowledge on techniques and benefits with other enthusiasts. This ‘open-source’ approach means that Passivhaus has spread rapidly around the globe. It also provides a reality check or peer review which drives performance up.

As Passivhaus grows in the UK over the next few years the worst thing we could do is to keep all this learning to ourselves. At Inbuilt, as well as designing real Passivhaus buildings, we will be passing our know-how to others through training and organising tours to see Passivhaus buildings in Germany and Austria.

Read more about Inbuilt and Passivhaus at: www.inbuilt.co.uk/html/passivhaus.htm