Cob appropriate climates

[Shannon C. Dealy]

On Sat, 7 Nov 1998 s.zeidel at utoronto.ca wrote:

> I was looking over a few of the cob websites and was wondering about a few
> things. First, what is the weather restriction for this sort of building
> material? I live in Canada, and noticed that there are some cob workshops

This seems to be a fairly common question with most alternative building
materials, and the answer is both simple and complicated.  The simple
answer is that all of the common alternative building materials (straw
bale, cob, light clay, rock, thatch, whatever) are appropriate in any
climate.  The complicated answer is that it depends on how you use them
and what you are trying to use them for.  Each of these materials has
strengths and weaknesses so it may be necessary to mix and match materials
and techniques in order to meet your needs.

It is important to keep in mind that pretty much any material/technique
is appropriate for interior use, it is only the outer shell that has to
deal with the local climate.  Regardless of what you use for your exterior
shell, cob is appropriate for your interior plasters, fireplace, floor
(though you may need insulation below it in some climates), built-in
furnishings, sculptures, etc..  Personally, if I were in an extremely cold
climate, I would probably build a cob structure, wrap it in straw bale,
then wrap the straw bale with a very thin cob outer wall or very thick cob
plaster, probably a few inches thick.  The big disadvantage of this
approach is that it's alot of work, and some people may not care for walls
that are 3+ feet thick.  The advantages however I think are worth it:

   1 - The main cob walls will keep the interior temperature very
       stable and will provide solid structural support for the roof
       without the need for dealing with the compression issues of
       straw bale.  In addition, if moisture should ever get into the
       straw bales, the thick interior cob walls should minimize/eliminate
       any of the mold getting into the interior of the house, and it
       would also make it possible to replace the rotting straw in the
       bale wrap without making a hole through to the interior the house.

   2 - The straw bale wrap will minimize heat loss from the cob walls.

   3 - The thick outer cob wall/plaster will protect the straw bales from
       moisture.  If the outer wall is thick enough, you could dispense
       with bales altogether, and simply tightly pack the space between
       the inner and outer walls with dried local grasses or other 
       insulative materials.  It might be better to make this outer wall
       using wattle and daub or some other technique which is better 
       suited to thinner walls.

As always with cob, you need a high foundation and wide roof overhangs,
but this only applies to the exterior, so the thicker interior cob wall
should only need a minimal foundation/moisture break.

Shannon C. Dealy
dealy at deatech.com