The point of PassivHaus is to reduce energy consumption. That’s it. It is a design and construction method developed by Dr Wolfgang Feist over the past 20 years in Germany to reduce the amount of energy a house uses. It is not concerned with CO2 emissions, with sustainable materials, with embodied energy or embodied CO2. It sets two energy benchmarks — 15kWh/m2/yr for space heating and 120kWh/m2/yr to include space heating, domestic hot water, lighting, fans, pumps and main appliances. But this begs the question, is energy efficiency really all that matters?
It’s Not Mandatory
PassivHaus is a choice. Compliance with the Code for Sustainable Homes (CSH), however, is mandatory across most of the country. So if the self-builder chooses to adopt PassivHaus it will be as well as meeting the prevailing Code standard, not instead of.
CSH is ratcheting up from the current Level 3 (already Level 4 in some parts of the country) to Level 6 in 2016. PassivHaus, in terms of CO2 emissions, will do better than Level 3 and could scrape Level 4, but will not get to 5 or 6. We still need to develop the methods to meet those CSH standards and PassivHaus may lead us to believe we are already there.
Sustainability Matters, Too
Sustainability means considering materials, longevity and now, crucially, CO2 emissions. It means building houses that suit young and old alike, that can be adapted to meet changing needs over generations, that use replaceable materials. For the sustainable builder, energy efficiency is a factor within the overall design. Energy can come from a zero-carbon source and efficiency does not need to be the altar upon which all other things are sacrificed.
Lifestyle Has to Change
The energy split in a house built to 2010 Building Regulations standards is broadly 53% space heating, 19% hot water and 28% power. In a PassivHaus it’s broadly 12% space heating, 32% hot water and 56% power.
Electricity becomes the dominant energy source, with its huge CO2 overhead. It’s said that energy-efficient living is 20% technology and 80% lifestyle. PassivHaus addresses space heating but not hot water and power demands. It is only lifestyle that affects these.
It’s More Expensive
The consensus seems to be that PassivHaus will increase build costs by 15% to 25%. The extra design work will be a big factor, but it flows through every element of the build. A triple-glazed, PassivHaus-grade window will cost around £350/m2 while a double-glazed window with a U-value of 1.4 will cost around £220/m2. PassivHaus doors will cost 60% more than conventional doors. PassivHaus requires an obsessive attention to airtightness detail and that impacts on glues, mastic, tape, grommets — the things we would not normally think about.
Then there is certification — a similar process to CSH compliance where evidence of conformity must be produced. The certification itself will cost £2,000. Testing and evidence gathering could add another £4,000. And that’s on top of any CSH requirements. There are some 8,000 certified PassivHauses across Europe and said to be three or four times that number of ‘nearly passive’ houses — built to the standard but not certified, perhaps because fuel bills have more impact on sale value than a certificate could ever have.
Code Level 5 is Stricter
Consider a 200m2 house built to CSH Level 3 standard. The build will need airtightness between 7m3/hr and 5m3/hr, use low-energy lighting, solar thermal and a gas boiler with underfloor heating; energy consumption will be around 83kWh/m2, which translates into CO2 emissions of 5.6 tonnes per year.
If that same house is built to PassivHaus standards, probable real energy consump tion is around 140kWh/m2 (the 120kWh/m2 plus those other power usages not included in PassivHaus standard). But the calculation is more complicated as the 120kWh/m2 standard refers to primary energy. That is, energy going into a power station, not to the house. If we assume the PassivHaus is all electric then the energy entering the house is only 27% of that figure — the other 73% being power station and Grid losses. That translates into CO2 emissions of 3.9 tonnes per year — a reduction of 30% but still some way short of CSH Level 5 or zero carbon.
What it means is that the CSH provides stiffer targets than PassivHaus — and that is the way the legislation is taking us. And, it might be said, the CSH addresses all issues relating to sustainability — rather than the perhaps narrow nature of our current PassivHaus obsession.