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Cob: RE: Re: Thermal Mass and R-valuesMichael Saunby mike at Chook.Demon.Co.UKTue Aug 3 11:47:05 CDT 1999
On 03 August 1999 17:06, Raduazo at aol.com [SMTP:Raduazo at aol.com] wrote: > Mike, > If you have the money to buy sheets of polystyrene you might try making > the wall by standing up the sheet on edge with the 4' dimension vertical and > the 8' dimension horizontal and then start building on either side then every > so often poke a stick through the foam to bond the two independent walls > together. The sticks extending through the foam will allow the two walls to > act as a single unit and give you the equivalent strength of a single thick > wall while the insulation will prevent heat transfer through the wall. > Ed I guess you meant this to go to the list, or another Mike. Personally, and I expect others on the list would have similar reservations - 1. It's an untried technique so you'd need to figure out a decent experimental method. How to simulate many years of thermal changes (daily and seasonal). Physical impacts, my own cob house suffered a serious shift in the roof, I don't know when, maybe a century or more ago. etc. 2. How would you calculate if this is worth doing? Over how many years do you expect to recover the extra costs of materials, and labour since your technique isn't without a degree of fiddling? 3. Polystyrene is really dangerous in a fire. 4. Polystyrene also acts as a moisture barrier. Is this good or bad? 5. Polystyrene carries an environmental cost that many will not tolerate. Don't get me wrong, I'm not anti-experimentation, it's the basis of all worthwhile learning but you need to have some idea of what you're hoping to achieve. If it's only going to save a few quid a year, why bother? If it could save hundreds for little extra cost then it might be better than some of the alternatives. BTW in the US do you have tables of heating costs vs. R values of materials? How do you decide what amount of insulation is worth installing if you want to get a payback in 10 or 15 years? Right now I'm working on a (mathematical) model of the dynamic thermal behaviour of cob walls. I've got other stuff to do first though so it'll be a while before I post it to the list. I'm hoping it will start to answers some of the questions of whether to insulate or not, and if the answer is yes whether to place insulation between walls, on the inside or outside. It might help answer some other questions too. Anyone else done this? Or even done the calculations for the steady state? Michael Saunby
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