Cob: Cold Temps

[Shannon C. Dealy]

On Sat, 10 Aug 2002, Do wrote:

> Hello all,
> I've been seeing a lot of discussion on flood plains, heat, humidity and air
> flow, but I have a question on how to build a better cob house for the cold.
> I live in a small town in the Colorado Rocky Mountains and it regularly
> gets below zero overnight in the winter.  In addition, the snow load on the

Generally, for climates with continuous extreme temperatures, I would say
to go with an exterior insulation wrapping the cob walls such as straw
bales, and I think this is probably a good idea in your area as well
(though maybe it's unnecessary for a sun exposed south wall if you get
winter sun on your site).  If you have good winter solar exposure, you
might be able to get away with less insulation with a proper solar design.
The important thing to remember with cob is that what your 24 hour
temperature extremes are is completely irrelevant, what you are really
interested in is things like 24 hour temperature averages, multiple
day temperature averages, and what you can do to shift these averages
toward your comfort zone through proper building design for your site
(such as using solar gain).  The temperature of the cob is not going to
shift significantly over a period of one night, it may take days or even a
week or more to really shift the temperature of uninsulated cob.  How long
it takes to shift it by some arbitrary amount is a complex interaction of
various factors including: wall thickness, straw content of cob,
average temperature difference between the wall and outside air, air
pressure, humidity, and average wind speed, not to mention any thermal
gain you get during the day from sun exposure

> roof would be very heavy. (A good winter will see a couple of feet on the
> ground at all times).  Are regular cob walls strong enough to handle this
> snow load (it seems they would be).  Does anyone have any experience or
> advice on this?  How do I keep it warm in the winter and cooler in the 90

Properly designed and built cob walls should easily handle the weight of
many feet of snow on your roof, though depending on the design of your
building and roof system, you may need some kind of a top plate/bond beam
on the top of your walls in order to evenly distribute the weight of the
roof supports since extremely heavy point loads on a cob wall can cause
problems with cracking at the point of load.

> degree summer weather?  And since the summer days are 90 and the nights are
> 40-50, is there something I need to consider with that extreme temperature
> difference?  What other things would I need to keep in mind?

Actually, for your summer temperature swing, plain, uninsulated cob
sounds ideal, since the temperature of the cob tend towards the average
temperature which it sounds like would be around 65 to 70 degrees.
Of course for year round temperature control, you will probably need to go
with insulated cob unless you can reliably capture enough solar energy in
winter to maintain your building temperature, without causing significant
solar gain during the summer.

Shannon C. Dealy      |               DeaTech Research Inc.
dealy at deatech.com     |          - Custom Software Development -
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