Cob: Re: Thermal Mass and R-values

[Tom Fetter]

Hi Tony.

Based on what folks said in reply to my similar query a while back, I'd 
probably encase strawbales within a cob wall -- more cob on the inside of 
the house (for structural and mass reasons), and either a thinner cob wall 
on the outside of the bales, or a thick mud plaster (which, if straw is 
incorporated, amounts to much the same thing).

It will be important to have a good, high foundation with a damp barrier, 
and significant overhangs.  This is to protect especially the bottom portion 
of the wall from splashback, and keep it dry.  It will go a long ways to 
prevent flaking and cracking due to moisture in the cob freezing.

I'm inclined to include strawbale insulation all 'round the house, including 
the south side, and rely on south facing windows for solar gain.  In Ottawa, 
as in Edmonton, there are enough truly long stretches of cold in the winter, 
that I'd be afraid of too much heat loss.  What may be fine in Arizona, 
Oregon etc. I think just won't be workable in the kind of climates we live 
in.

It also occurs to me that it may be possible to build somewhat higher 
"lifts" of cob in this technique - the strawbales would act as one side of a 
form, and may give enough added some support to the mix to prevent slumping 
'till the courses were a few inches higher.  Sticking some bamboo stakes 
etc. through the strawbales into the cob on each side may also prevent bale 
settling -- both sides of the bales would effectively be held in place by a 
masonry wall.

BTW, if you get private responses to your note, I'd love to be copied on 
them, if the senders agree.

Tom Fetter.

>From: Tony Glaser <aglaser at engsoc.carleton.ca>
>Reply-To: Tony Glaser <aglaser at engsoc.carleton.ca>
>To: coblist at deatech.com
>Subject: Cob: Re: Thermal Mass and R-values
>Date: Tue, 17 Aug 1999 15:58:49 -0400 (EDT)
>
>
>
>I want to build a cob home in Canada where it sometimes gets as cold as
>-35 degrees Celcius, so I want to be clear on this issue which you cobbers
>have been discussing for some time (as I see in the archives).
>
>As I understand it, thermal mass is how much heat your walls can store,
>and insulation is how slowly heat is put in or taken out.
>
>If Cob has a high thermal mass and a low insulation, that must mean that
>you can store a lot of heat in it, but the heat also enters and leaves
>quickly.
>
>So in the winter I want the outside of my wall which faces away form the
>sun (north) to be as insulated as much as possible, all of the time.  The
>side which faces the sun should be insulated as much as possible at night,
>but in the day insulated _just_enough_ so that the sun can transfer it's
>energy into the wall at the rate it wants to.
>
>In the summer, I wan't shade and no insulation, but lots of thermal mass.
>(Which is why cob is so great for warm climates.)
>
>So as far as I can tel, the easiest thing to do is stack straw bales
>around the shaded parts of your house in the winter (adding some to the
>front at night if its cold enough to freeze the balls off a brass monkey),
>and move the bales away in the summer.
>
>I guess an advantage to this is that the bales will collect snow, which is
>itself a great insulator, and looks pretty.
>
>This is what I'll do unless someone has some better advice.
>
>Thanks,
>
>Tony
>
>--------------------------------------------
>Anthony Glaser
>aglaser at engsoc.carleton.ca
>http://www.engsoc.carleton.ca/~aglaser
>Year 2 Electrical
>Faculty of Engineering, Carleton University
>
>


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