10 Feb 2007

Are Passive Houses the answer?

Tomorrow I am off on a Passive House (PassivHaus) study tour. I take an evening flight to Hanover and join seventy others at the Loccumer Hof Hotel for a day of lectures on Monday followed by a full day’s itinerary visiting three PassivHaus sites. Sandwiched between this is a gala evening meal at Hanover City Hall for which they have thoughtfully emailed us the menu. It looks to consist of about half the annual produce of Lower Saxony and I don’t anticipate many of the guests will be clubbing into the small hours after that lot.

For those of you who know little or nothing about Passive Houses or, more specifically, the PassivHaus standard, I can’t do better than to suggest you mug up at the relevant Wikipedia page.

The Passive House concept is beginning to get wide coverage in the UK media. It’s seen as the most advanced example of low energy housing anywhere on the planet and over 6,000 have been completed to date, mostly in Germany and Austria. In the UK, the BRE have taken it under their wing and it is they who are organising this study tour. The question we will no doubt all be asking is: “Is this the future of low carbon housebuilding?”

Whilst there are lots of plus points, there are also serious doubts in my mind about whether the PassivHaus standard is the perfect solution. In particular, what irks me most is that it sells itself as a performance standard – it is quite specific about just how much energy can be consumed per square metre of floor area — but it also adds several other stipulations about what you can and can’t include in a passive house. For instance, you must have mechanical ventilation with heat recovery, whether you want it or not, and you must have windows with ultra-low U values. Why is it so prescriptive about these items? Are they saying you can’t meet the performance standard without these features? Or is there some other reason for including them?

They say that passive houses can be either masonry or timber frame? But German timber frame is very different to British timber frame: is our local version of timber frame suitable or does it need more thermal mass? What about using other build systems like SIPS or ICFs?

There are also lots of issues to discuss like costs and transferability to other nations? As discussed on the blog recently, the UK has the smallest homes in Europe. It’s harder to lose 300mm of wall insulation in a rabbit hutch. Does it make sense to do so? And does the standard restrict house design to the rectangular box? Or can it be adapted to the more varied UK styles?

Another issue is the requirement for triple glazing: is the extra expense, not to mention the embodied energy used in manufacture, ever justifiable in the British climate? In fact, I hope the whole house embodied energy argument gets aired. It’s hardly worth reducing the annual carbon emissions from 5 tonnes to 2 tonnes if it’s going to take an extra 60 tonnes of carbon to manufacture and build. Whether it does or doesn’t, I have no idea. But it’s the time and the place to speculate about these issues and I’ll be posting my answers when I get back mid week.

1 comment:

  1. I have to agree most with this topic. The solution of technical requirements behind it and the creation of a good price-performance ratio is task of the product manufacturers of passive houses. In this sense demands for the advancement of concepts, components and of passive house architecture are to be made. Keep working, we will be there!