Transition Culture

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2 Mar 2006

Eco-Build ’06. Talk No.3. Chiel Boonstra – The Passive House.

passiv**Chiel Boonstra** is a Senior Consultant DVH Building and Industry Sustainability Consultants and a specialist in the Passive House model. His lecture focused on the Passive House, which is a concept for a house which requires no space heating at all. Clearly there is a lot that can be learnt from this excellent model which will be needed in post-peak housing. However, there is a catch.

Boonstra began by saying that old buildings use 180 Kwh per m2, low energy buildings between 75 and 40, and the Passive House as little as 15. There are now as many as 3,500 Passive Houses in Europe, the concept dating back 15 years. The key to them is that they are incredibly well insulated, and well detailed. The windows are triple glazed, the buildings are airtight, have good ventilation and also heat recovery systems. They also make good use of shading to prevent overheating in the summer.

pvOne of the essential elements is that they rethought the wall system, so that rather than a solid wall with insulation in the middle, the whole cavity is insulation. They use these amazing windows, with triple glazing and U-values as low as 0.8. They have also been using the Passive House model when retrofitting buildings; he showed a tower block in Germany that had cut its energy needs from 200KWh per m2 to 26, using these principles.

The catch I alluded to above is twofold. Firstly, one key flaw with the Passive House is the materials. The Passive House uses a lot of concrete, and also rather unpleasant expanded foam products made from petrochemicals for its insulation. Despite offering a model for houses which can carry people into energy descent without the need for any heating, the degree of embodied energy in the materials was not mentioned once.

What interests me is whether or not it is possible to build a Passive House using materials from within a, say, 15 mile radius? A colleague of mine here in Totnes is doing his MSc dissertation for the Sustainable Construction course he is doing focusing on this concept. If it can be done, then it becomes an essential part of the Energy Descent Action Plan, setting a target when all houses will be built like this and back casting what needs to be put in place in order to achieve that. The Passive House shows that zero energy housing can be achieved, but at the same time throws down the gauntlet to the natural/local building movement to try and match it, to take that as the benchmark to compare our buildings against.

sbThe other thing about the Passive House is that they are almost all, to my eye, pretty ugly buildings. For me, beauty is almost as important as energy efficiency. The Cob Cottage Company talk of ‘building homes so beautiful they make grown men cry’. Don Beck, one of the experts on Spiral Dynamics, says that rather than informing people about the environmental crisis and expecting them to act, we should “design the habitat

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Tom Atkins
2 Mar 10:23am

The Eco-Build thingy sounds like it was great – wish I’d been there and thanks for your opinions on it Rob.

Aha – passive houses! Well, we’re about to embark on an ‘almost’ passive house here in Ireland. It could be fully passive but we really want a small wood-burning stove for heating, hot water in the winter, for boiling the kettle and for the soul. That said, we’re looking at a tiny stove with a 3.5kw output for the whole 120m2 house.

Is the house local? Well no, it comes from Sweden and will be supplied by Scandinavian Homes. On their website you can see examples of the houses built so far including Ireland’s first fully passive house which will be used as their offices. We visited this and it was very pleasant to be in.

Although they currently come from Sweden there is no technical reason why it couldn’t be made entirlely in Ireland. We asked why they don’t use Irish timber. The answer was not anything to do with the inherent quality of Irish wood (some say it grows too fast) but rather that the timber mills were not able to produce sufficiently accurate finished product in Ireland. The timber itself is fine.

As for the other materials, there is not concrete or expanded foam in the shell of the house – it’s all breathable rock wool and warmcel (recycled newspaper) in the roof which I personally have no problem with from a sustinability point of view. The foundations are admittedly a thin slab of concrete – but you could use lime if you wanted.

Even importing the timber from Sweden or Canada (as you mentioned recently) is not such a bad idea. I suggest that slow boats will be navigating the oceans long after we’ve all stopped driving the SUV to Tesco’s. A big slow boat hardly adds to the embodied energy of non-preishable goods. (I’ll do some maths on this soon – or maybe George Monbiot will beat me to it!)

As for not needing much fuel when running the house this is THE most important aspect – and I’m pleased you’ve given very energy efficinet houses some air-space. The information here here and here shows just how unimportant (relatively) the construction phase of building is. It’s much lower than the 20% energy use over building life-cycle suggested in an earlier posting. A crucial aspect in our damp cold climate is a ventilation heat exchanger – as Quentin Gargan says – a ‘no-brainer’ – but to make one of these work well, you need a ‘tight’ house, and to make a ‘tight’ house you need precision construction. This is hard to achieve outside of a factory.

So, onto beauty – you’re right Rob – a precision built passive house will struggle to match the beauty of a hand sculpted cob house. This is a trade-off that only the person who the house is being built for can make. Beauty is in the eye of the beolder and for me, knowing the good that something is doing makes it more beautiful – I find wind turbines quite gracfeul – but suspect if they were spewing out noxious gas I would find them less so. Thus a nearly passive house gains beauty with knowledge. (And Ruth has convinced me to go with a turf roof – so it will look pretty gorgeous, even though we’ll be wasting 120 square metres of potential roof water for drinking!)

Does anybody have figures for heating (watts per metre squared) for various cob houses? I suspect Kevin McCabe’s Aga in his house in Devon is chewing it’s way through a lot of fuel… We need good figures for cob houses including the additional time / energy spent fitting things into curvy spaces 😉

If we are to use wood for heat and hot water we need to use as little as possible. I’m hoping not to have to spend too many hours a year chopping and stacking wood. For those who live in large towns and cities, completely passive houses are perhaps the only way to go in the long term – how many acres of forest would we need to heat London with wood?

One very important thing you got me to realise was that it is important to build houses that last a long time. The estimated life-span for these timber houses in the Irish climate is 250 years. Not as long as a cob house, but not bad and plenty long enought to grow new trees for the next building.

Perhaps the biggest thing that I will be missing that the natural building movement taught me is that if we were hand building our own house we would gain empowerment, removal of need for loans / large cash lump sum, and less need for specialist designers. I feel that this is where the emphasis for post-peak building must lie – people may not have access to loans and structural engineers in the future and in this landscape local natural materials offer a very important function.

So, to emphasise your last point Rob – I totally agree that the next challenge for the natural building movement is to make precision methods (draft prrofing, ventialtion heat exchange etc) with accurate total life-cycle energy figures available to the local natural builder. The romance attached to natural materials is there for a reason – they are healthy, beautiful, sustainable and local. But this alone won’t help if the end result is expensive and poor performing from an energy point of view.

But then, perhaps with declining populations and larger households (people moving back in with each other) we won’t need to do much building for the next 100 years. Long live the retro-fit!

4 Mar 4:20am

Rob – I like the article’s focus on doing better that the commercial package.
You mentioned a friend doing an mscon the issues ? Well last summer I bought about 25 fleeces (as sheared) from my neighbour here in the Welsh Marches, aiming to have a go at laying up, pressing & rolling them as a alternative to fibreglass and expensive wool blocks –
Sadly I’ve had no time this winter and things are getting busier, so if he’d like them to experiment with, rather than waiting till June, I’d be glad to hear from him.



Thomas Heufers
1 Feb 7:53am


If somenoe is interested we can offer passive houses (wood construction) with an eletricity consumption under 3.000 kWh per year.

Take a look on our website.
For further informations phonecall 0049-5231-569596 (Germany).

We sell europewide.