Cob: RE: Insulation

[Sojourner]

Otherfish at aol.com wrote:
> 
> The point I'm wanting to make is, think of your building like
> an organism - lots of animals get furry for warmth in the winter.
> Why can't a house do that too?  Simply stacking bales around the
> outside of the building would accomplish this.

Firstly, let me say I'm not trying to totally denigrate this idea, but
only to point out some potential problems and alternatives.

I personally wouldn't have exposed strawbales stacked around my house.

In the first place, they are going to get wet and rot.  That means you
have to do it all again - first hauling off the rotting straw bales.

Straw bales are heavy, they weigh anywhere from 65 to 80 lbs each. 
You're talking about an awful lot of work.

In the second place, the problem with places like the NE US and the
Midwest is that it gets cold enough in the winter to need insulation to
maximize your heating efficiency, and hot enough in the summer to need
insulation to maximize your cooling efficiency.

One solution, probably the BEST solution for these types of climates
(where you have both extremes of temp to deal with at different times of
the year) to this problem (of regulating internal temperatures) is to go
underground.

But not everybody wants to live underground - it can be very
claustrophobic.  Also, building underground comes with its own set of
problems that not everybody wants to deal with.  Requires a lot of
excavation, heavy equipment, or back-breaking labor, among many other
things.

You can earth-berm.  I'm not sure if you can use cob in an earth-berm
situation - if you can, then that might be a solution that'll get you
some natural temperature regulation and still let you have the cob.

Again we're talking a fair amount of heavy excavation, again its not
something everyone wants to live in.

A straight cob structure is going to be difficult (not impossible, just
difficult) to regulate the internal temperature, at least with the
thinner walls that people on this list seem to be favoring.  I never
heard of a wall thinner than 2' or 3' thick discussed on this list years
back, but maybe my memory is faulty on that point.

I think we have a guy from Devon posting to the list?  It is my
understanding that the cob structures still standing in Devon actually
have walls on the order of 3' to 4' thick.  Is this correct?

If so, perhaps if you really really want a straight cob structure in
such a climate (which, after all, is most of the US) the thicker cob
wall might be a potential solution.  If you get a thick enough wall, its
going to have SOME insulative properties at some point, no matter how
low the natural insulative value is per inch.  Going with an estimate of
.25/inch which I have seen mentioned on this list recently, a 4' thick
wall is R12.  R12 may not be enough for Minnesota or places where the
weather gets that kind of bitter cold, but for most of the midwest and
much of the NE, R12 combined with seasonal shading, orientation to
whatever amount of sunshine you can count on, windbreaks, etc, MAY be
enough to get you over the heating/cooling hump with some reasonable
expectation of efficiency.  It's up to the guy building the house to
decide what they'd be satisfied with.

But if you're going to use strawbales to insulate, it seems a better
solution to just build them into the wall to start with, plastering over
with cob.  Then you have a nice, roughly 2' thick (by the time you
plaster inside and out) wall that looks just like cob, and you have
permanent insulation.

This means you don't have to haul 80 lb bales of hay around your house
twice (or more) a year, concomittently having to haul off the rotting
stuff.  (Of course, if you want it for your garden as mulch anyway,
maybe that's not such a hardship <VBG>)

You don't have to pay up to $4 a bale more than once - the cost of straw
and hay has been very high lately.  In some areas where wheat is grown
by the thousands of acres it may be more affordable, but the most common
prices I have seen for small square bales of hay or straw is $4 a bale
or more.  Occasionally I have seen them in the last year for a bit less,
occasionally a bit more.  I live in rural (very rural) MO, where straw
is actually more expensive than hay, and hay goes for these prices. 
Straw is more.  Check in your locality, prices vary.  In any case you
are talking a yearly expense at the least.  Count on hay/straw prices to
increase as time passes.  Most farmers I know couldn't imagine a $4 bale
of hay 10 years ago.

Extending your roofline out say 3 or 4' may help minimize this problem,
but it won't help with the rest.  Again, this is an additional expense,
but may be a reasonable one - the extended roofline will also serve to
protect your cob walls and to shade the house in summer.

You don't have to worry about animal or insect infestations in the
exposed bales, right up against your house, where rodents are like as
not to gnaw through your earthen walls.

And you don't need to worry about the kids climbing the stacked bales
and knocking them down.

If you're going to coat them over with a mud plaster to avoid many of
the above mentioned problems, to me it makes the most sense to just
build them into your walls to start with and have done with it.  YMMV.

Another problem I haven't mentioned before is code.  Even in many
seemingly rural areas, people still have to deal with building codes. 
If you're going to try stacking exposed strawbales around the outside of
your cob home (that you probably already had to fight to get a variance
for, unless you are fortunate enough to live in an area where there are
already cob codes in place) you are exposing yourself to additional
problems with the exposed strawbales.  You may get away with it for
years and years and years, or you may not.  Just something to consider.

Holly ;-D