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Turf rooves: Good, bad, or ... ?

Occasionally you see a turf roof on a building, and I always wonder whether turf rooves are a good idea or not. The Six Cities design festival in Inverness is focussed on ecological housing so this was the perfect time to find out.

I've read about and seen the traditional Icelandic turf houses. But Icelandic farmers of the past had almost no other building materials available, so it's hardly surprising they tried making houses out of turf. And besides, modern Icelandic housing has completely jettisoned turf rooves, which suggests there might be arguments against them.

Yet, various eco houses do have turf rooves - in Inverness there's the Glachbeg Croft Education Centre, for example, and the library of the Great Glen House, which according to the festival guide has "a sedum turf roof that retains heat better and is a home for insects, plants and birds." Sounds good. But if anyone is in need of heat retention it's the Icelanders, so why haven't they stuck with them?

I can think of a couple of disadvantages of turf rooves. In particular, sticking with the eco theme, we may want things like solar roof panels, or large windows set into the roof (to cut down on lighting/heating bills...), so those would "compete" with the turf for roof space... but those are recent innovations and anyway, they can presumably live side by side.

Perhaps maintenance? The big question I don't have an answer for is how much maintenance a turf roof needs. Would you really want to have to get the stepladder out and trim/weed the roof every now and again? (BTW see later for more on this)

Returning to the Icelanders, there may be a completely different reason why turf roofing is passé. Since it is cheap, simple, and has a very obvious appearance, maybe it picked up strong associations of poverty and farming. It does seem that Reykjavik's early urbanites felt it much more fitting to use corrugated steel for their rooves, with its modern appearance and bright painted colours. (It did puzzle me when I saw all the corrugated sheet metal around Reykjavik - is that really a suitable material for building warm houses, resistant to the briney sea winds?)

So for me the question is still wide open. Could turf roofing be a sensible option for a row of ordinary houses in the middle of any old town?

UPDATE 2007-05-29: Today we visited the Findhorn eco-village, where there are some turf rooves dotted around, so I asked the guide. He said that turf rooves are essentially an aesthetic choice - they are decent for insulation but have to be quite thick (for moisture retention), meaning the house needs sufficient buttressing to support the weight. So they're not particularly cheap option or with strong benefits. They also need a relatively shallow roof: less than 20% slope for grass, but sedum works better and on more slopey rooves. The guide said they typically strim their grass rooves once or twice a year, so the maintenance is not very difficult.

UPDATE 2007-06-03: wikipedia has a decent article on turf rooves.

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