[GSBN] Question about SB insulation at foundation/ceiling
derek at unm.edu
Tue Jan 24 09:16:06 CST 2012
I'm not sure if this discussion is still alive on the linked site that Joyce posted. The newest posting is just about a year old, but perhaps the discussion will warm up again. Bruce King posted a comment last year, when the discussion was current.
Something that wasn't mentioned in the article or comments is the naive assumptions regarding the effective insulation value of the strawbale waffle slab design, even before the bales start to rot. The assertion is made, and not challenged, that the under-slab strawbale insulation would provide R-50. Whatever number we accept as the insulative value of each bale, the thermal bridging of the concrete in the matrix would cut the effective insulation of the waffle slab design dramatically. Thermal bridging isn't a problem with the design sketch that Joyce included, but the risk of rot probably remains.
There is an alternative approach that uses bales as floor insulation, but above grade. After a European Straw Building gathering a few years ago, traveling with Catherine Wanek, I visited SB buildings in half a dozen countries, including several that used strawbales in the floors, to meet Passiv Haus design goals. All of these structures were build on piers, so that the bales were above grade and isolated from the moisture concerns that afflict buried bales. Here is a link to one example, the S-Haus in Austria.
derek at unm.edu
On Jan 23, 2012, at 10:40 AM, Frank Tettemer wrote:
> Well now,
> that is pretty interesting.
> Thanks, Joyce, for sounding the alarm.
> Before I actually (physically and personally), had built any SB houses, I naturally ass-u-me-d that bales in the floor and ceiling were a good idea.
> It is too bad that the article in finehomebuilding references the experimental work of Michel Bergeron, of ArchiBio, in the ground-breaking book of Steen/Steen/Bainbridge/and Eisenberg. I love the book, and it is what gave me hope for the idea of burying bales below grade.
> Fortunately for me, Linda Chapman, (archi. from Ottawa), talked with me about doing this in the early nineties.
> She had boldly gone where no one had gone before. And the floor rotted.
> And there was the evidence from the huge three-story yoga retreat centre, built in Quebec,
> which was such a rotten embarrassment, that I won't mention it anymore.
> Then there's the theory that if you stick each bale into a garbage bad before you bury them under the floor ...
> just to say I did, I took a bale, put it into a garbage bag, and placed it into a weather-protected shed, to see what happened.
> First of all, it took three trys with the garbage bad to place a bale into it, without it being punctured by straw.
> Secondly, during the summer of 2000, which was a fairly wet year, the bale self-composted, with out having had a drop of rain on it. I imagine that relative humidity was all it took. It was full of mildew in two months time.
> I have to say, though, that the idea is so intriguing, that it captures the imagination of quite a few clients, who would wish me to design a foundation using straw bales.
> Maybe it's just a stupid idea, here in a climate with huge weather extremes, (+35C to -35C), and many days of damp rainy weather?
> Maybe all the ideas have not been tried as yet?
> Frank Tettemer
> Living Sol ~ Building and Design
> 613 756 3884
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