Cob: RE: Re: Thermal Mass and R-values

[Michael Saunby]

On 26 July 1999 14:24, Mike Carter and Carol Cannon 
[SMTP:cobcrew at sprynet.com] wrote:
[SNIP]
>> >If so what would be the trade-off between structural material, i.e.
> >something that will hold the roof up, vs. insulation which will just
> >collapse under the weight?
> I think this is the wrong question.  The trade-off is between the cost of
> the insulation materials and whatever heating/cooling would otherwise be
> used over the lifetime of those materials.  If we can't come up with a 
good
> way to add insulation to cob walls, I will start building thicker walls
> (currently averaging 22" at base).
>

OK.  But in that case you've got (at least) two calculations.  One for 
insulation, cost of materials and installation, vs fuel costs over the 
lifetime of the material (or the structure if less).  Then a second for the 
cost of providing a weatherproof, (beatheable ?) physical shell.  If you 
want to factor in the energy use and pollution involved in each option then 
that might change the choices too.

To be honest I thought the trade off between energy use and cost of 
insulation was a no-brainer but choices of fabrics for the shell seem 
somewhat harder because the choice you make is what creates the insulation, 
or lack of it, problem in the first place.  Glass, brick, stone and 
concrete are even worse because their insulation is worse than cob. Wood or 
straw (when dry) are rather better insulators than cob, but solid wood 
buildings are no doubt expensive, and straw has its own problems.

Michael Saunby