24 Oct 2014

Whither Passivhaus?

Last week I attended the 4th Annual Conference of the UK Passivhaus Trust. On many levels, it's all been a super success with the number of UK projects burgeoning towards the 250 mark and expected to get to 1,000 sometime in 2015. Interest is growing far and wide beyond the little core of activists who launched the trust back in 2010.

But of course it's still very small fry when set against the total amount of building going on and there were voices to be heard saying that maybe, just maybe, Passivhaus isn't quite the way forward we thought and hoped it would be. It sets out to be an exacting target and therefore an expensive one to meet. Whilst for new builds it looks eminently achievable and economically justifiable, in the retrofit market Passivhaus has the feel of being overkill. The structural changes you have to undertake in order to get an existing house to EnerPhit, the reduced retrofit standard, are so great that you begin to wonder whether it is really be worth the bother. Only a very keen energy wonk is ever likely to undertake an EnerPhit conversion: fuel prices would have to be an order of magnitude greater than they are now to make economic sense. Even the environmental sense is questionable.

There were lots of very interesting presentations. Caroline Martin of WARM caught my attention with her analysis of post-completion testing of a number of Passivhaus homes in the West country. The usual spread of outcomes was on display — there always seems to be a joker in the pack who leaves all their windows open throughout the winter and shows up as a total energy hog, and Caroline's sample didn't disappoint in this respect.

But there were also a handful of homes where the heating hadn't been put on at all during the winter. "Was it a particularly mild winter in Exeter?" she asked herself. Weather stats showed that it hadn't been — it was very average. So these homes hadn't just met the fabled Passivhaus space heating standard of 15kWh/m2/annum, they had scored zero kWh/m2/annum. This set me wondering whether they hadn't been over engineered. The design idea is not to eliminate heating costs altogether, merely to reduce them to a very low number and presumably the cost of getting the score down below this is deemed to be money wasted.

In general, the Passivhaus standard is responsive to weather data, thus making it easier and cheaper to build in warmer climates, certainly as regards the amount of insulation to be built in. Conversely, it is much harder to build in colder climes and this has led to a revolt in North America where many low energy enthusiast feel that the standard is just a little too German and that different climates would be better served by variations on the standard. Their specific beef is that when you get into the far north of the US and Canada, the wall insulation becomes unrealistically (and pointlessly) thick. They argue that it would be far cheaper and more cost effective to generate a little electricity on site than to build to an arbitrary standard which is optimised for central Europe.

Now Passivahusers have long desisted from offsetting their heating standard with renewable energy. "No green bling, let's keep it simple" went the oft repeated refrain. But now it appears that the Passivhaus Institute in Darmstadt is about to jump aboard the green bling bandwagon and start offering alternative Passivhaus standards which incorporate on-site energy generation. Watch out for Passivhaus Plus and Passivhaus Premium. Old die hards will have to make do with Passivhaus Classic.

It seems that politics is at work here. I couldn't quite get to the bottom of it, but the EU is pointing us towards a new target, the Nearly Zero Carbon Building, and it will be requiring that these have some form of onsite electricity generation. In this light, if Passivhaus is to stay relevant it has to bring PV into the equation. It also has to take into account not just the primary energy used (a lesser known target of the Passivhaus standard) but the carbon intensity of that primary energy.  Hence the new versions of the standard referring to carbon intensity of energy used.

But in doing this, the Passivhaus standard starts to resemble other standards (like the Code for Sustainable Homes) which no one much loved. I fear they may be a small backlash amongst British and Irish enthusiasts who set their stall out on the simplicity and robustness of the original standard. But a full scale American-style tea party revolt? I don't think so. You might not guess it from our newsprint, but I think we are just a little too European for that.


  1. Gd post, even tho no comments - keep goin!

  2. A German Passivhaus friend and colleague says the British don't revolt, they "tut"

  3. I expect that the “no heating” may be due to having an old computer running 24hrs a day, or other such heat sources.