27 Oct 2011

On 2011 UK Passivhaus Conference

Monday and Tuesday this week saw me at the 2nd UK Passivhaus Conference at the Barbican Centre in London.

There were around 250 attendees consisting of a fair smattering of old AECB-heads, a fair few BRE types, a sprinkling of academics and a good gaggle of "people who had come to learn." Consequently, the conversations ranged from the basic "This is what a Passivhaus is" through to the arcana of extreme building physics. The Passivhaus Trust itself would seem to be in rude health, energised by the fusing of the AECB's enthusiasm with the BRE's clout and professionalism.

Not everyone in the sustainable building arena buys into Passivhaus as a concept. Some decry its enforcement of MVHR (mechanical ventilation), others are suspicious of its cult-like qualities — it's very much the brain child of Wolfgang Feist and he gets to decide who and what gets certified, as well as remaining the owner of the PassivHaus Institute. But the beauty of PassivHaus is that it's a relatively simple standard, it appears to be based on solid building science, it's been shown to deliver what it says on the tin, and it's an internationally recognised standard, thanks mostly to the tireless promotional work of Feist himself. And in the UK in particular, Passivhaus still represents a giant leap forward on current building standards, even low energy ones, so it's not hard to see why the green building movement (OK some of it!) is so keen to promote it.

Day Two was for me the more interesting. It delved into a variety of technical topics and it would have been good to be able to sit in on them all, but the nature of the breakout sessions was that you had to choose one from three. Mark Siddall was particularly impressive on the subject of thermal by-passes and wind washing, a topic that lies beyond the confines of Passivhaus, but goes a long way towards explaining why low U value walls and roofs don't perform as designed. I also sat in on a good session given by Paul Tuohy (Strathclyde Uni) and Prof Chis Tweed (Cardiff) about the problems of post-occupancy monitoring. Everybody and their aunt calls for more of it, but the process is fraught with difficulties and the results are sometimes meaningless because there are so many incidental factors at work. Co-heating, in particular, was singled out as being hugely unreliable which is interesting because the practice involves keeping the temperature in a building constant over a long period and measuring the resultant heat loss, which reminds me of the tests run all those years ago by Actis to show that their multifoil was the equal of 250mm mineral wool.

Another observation was the ever growing interest in natural building materials and breathable fabrics. This is another area on which Passivhaus is silent: it emphasises airtightness above almost everything else, but has nothing to say on vapour permeability or embodied energy. Should these be included? Is there good practice to be passed on here or is it just getting too complicated?

And, more than once, the subject of quality control came up. Much of the success of Passivhaus is down to ensuring that the building is designed right and built right and the official or certified Passivhauses have to go through an expensive (like £2,000) and fairly rigorous auditing process. The materials need to be checked off, invoices examined, photographs taken. All very anal and tedious but critical in delivering quality. Some people are of the opinion that the certification process lies at the very heart of Passivhaus and is the main reason for its monitored success, but others feel that it's much too expensive and the certification cost needs to be reduced. It's a political point as well because Feist's PassivHaus Institute is resolute in insisting that they remain the police force here and they fear that any move away from this will inevitably lower standards. The UK Passivhaus Trust is firmly in Feist's camp but other countries (notably the USA) are taking a more relaxed view, claiming that the standards should be open and usable by all.

In one sense they already are. Anybody can look up what the Passivhaus standards are, anyone can purchase the design package (the Passivhaus Planning Package), anyone can claim to build to these standards. But where is the quality control? Without some form of rigorous certification process, how can you really know you have built a genuine Passivhaus and not a pale imitation that doesn't deliver energy savings as designed? It's a big issue, arguably the biggest one surrounding the Passivhaus movement. And it's interesting to note that of the 30,000 Passivhaus buildings constructed to date around the world, only about 10% have been through the official certification process.

Which brings me onto my final point, if it's the certification process which is the BIG THING, then maybe there's nothing much wrong with our building regs as they now stand, if only we built them properly.


  1. Your last point would certainly make a big difference to energy usage. I made a similar point as part of my 2008 article on the prospect of zero carbon housing - http://www.mikebriggs.org/zero - which also calls for a change in attitudes and culture across the sector.

    The other key requirement is to accurately calculate thermal performance at the design stage, whether or not achieving the Passivhaus standard is the aim. This requires a tool - such as the Passivhaus Planning Package - which is proven to be produce reliable results in low energy buildings.

  2. While I have read most of your post and agree BUT can you try and make them a bit more conscise?

  3. I like the long posts - If you've got a lot to say, say it.

    The text is written more in the style of traditional media (long paragraphs) rather than new media (plenty of sub headings and paragraphs about half as long). Apparently people find it harder to keep track of where they are when scrolling down a screen and linke having markers.

    Sorry that was totally off topic - it's true that passivhaus has a straight forward prescription which is clear and easy to understand. I think that's lacking from other methods.

  4. The comment about post-occupancy monitoring raises again, for me, the issue of what happens well down the line to a Passivhaus (and MVHR houses in general). One would assume that the first occupants will be completely up to speed with the systems and act accordingly but I know that my Victorian end terrace is not being lived in as it was designed to be (no doubt the builders and original occupants would be horrified by the thought of an inside toilet!). What happens when we need to radically alter our usage? What if we want to convert the front room into a garage so that we can re-charge our electric cars; what if we need to go back to three families in an average three-bed house; what if the area goes to crap and the house becomes a cheap private rental and then the MVHR breaks and the landlord is too tight to repair it; what happens when the third owners decide it's too stuffy and open all the windows and then find it cold so install bog standard gch... It is in the nature of high-tec that it becomes obsolete or stops working properly (anyone splash out on a mini-disc or DAT?). "Adapt or die". Can a Passivhaus adapt? I think that is the l;ong-term monitoring question.

  5. Please don't make your posts shorter Mark!!

    Have you read Mark Siddall's paper on quality assurance on the Passivhaus Trust website?

    I think that one of the strengths of PH is that it is a clear claim, unlike low energy or eco house.

  6. Doesn't do much to enhance the perception of estate agents....don't trim your posts!

  7. It seems to me that the greatest asset of the Passivhaus standard is that the performance is based on the building fabric but the greatest weakness is reliance on MHRV.

    I plan to self-build to Passivhaus standard but I'd like a simple efficient MHRV system that I can service myself so I do not have expensive maintenance costs. Are the Passivhaus recommended MHRV systems easy to maintain by the householder or is maintenance a factor to be added to the building running costs? Anyone know?

    As for getting the finished building certified - bring the cost down to less that a grand and I'll consider it in case I want to sell on, otherwise I'm with the 90% of other Passivhaus builders who want to spend their hard-earned cash on something a bit more useful that a piece of paper.

  8. Post length if fine by me but then I'm over sixty and don't suffer from the that modern affliction: a short attention span.

    I do prefer to design a passive houses rather than a PassivHaus, which are really active houses with all the kit and controls required. I do use and agree with all the standards, especially the airtightness but prefer to use passive stack ventilation. The additional heating load is about 1kW on a reasonably sized house which can be met, in rural areas where most of my designs are, by using a small wood stove. I also prefer thermally massive houses, where you can get several days carry over of heat, to typical PassivHaus lightweight structures. I like a house which just sits there and does its thing on its own with very little control or active input.

    Regarding embodied energy in materials, this only becomes significant if you are designing for a short life, say sixty years. In our energy constrained future we won't be able to build quantities of new houses, or alter significantly existing ones, because the energy to do so will be in short supply or too expensive or both. If you look at the age of some of our present housing there is no reason to suppose that a well built passive house won't last for three or four hundred years. So over that lifespan embodies energy is a very small proportion of the energy used in a building.

    Local and natural materials will come into their own as energy prices rise and a greater proportion of these will be used in the lower numbers of new houses built. Until then we have such a huge number of houses which require insulation, 25 million, that we will have to use any insulation materials that we can get hold of. That 25 million represents 625,000 per year or 2500 per working day to insulate to achieve an 80% reduction in carbon output by 2050. No small task!

  9. Mark - The difficulties of conductiing a coheating test are somewhat overstated - as you say, all it involves is heating up a house to a set temperature and measuring the energy required to maintain that temperature relative to the outside. At Leeds Met we have been doing this for 20 years and have found the test to be reliable and repeatable, and when used in conjunction with other techniques such as heat flux measurement, thermal imaging and trace gas decay it can tell you a lot about the quasi steady state thermal characteristics of a dwelling. Where there are discrepancaies between the design expectation and measured heat loss, then we can usually explain these quantitatively. The problem with the Actis tests on the swiss chalets was they were not comparing like with like rather than there being a problem with the test methodology.



  10. That's interesting, Jez. I remember a comment from someone at the BRE years ago that the test itself is somehow flawed and that is why the results vary so much, but maybe that was to do with the problems of getting two buildings to perform in the same way.

    I think the point being made about co-heating at the Passivhaus conference was that it was slow and cumbersome, not that it didn't work.

  11. Wow! Nice post! It's more than informative! I'm currently remodeling my house and I'm thinking of making an upgrade to my insulation. The budget might be too steep but hopefully I can make it work. I didn't know where to start but I got some ideas from your post. Great work! Thanks and more power to your blog! Cheers!

    Kevin Akins- kevinrakins@nuhrd.com