Cob: COBB AND INSULATION

[DoNegard at aol.com]

Holly
<<> 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.

<>
Isn't this is a matter of personal taste?  I don't see how taste affects 
insulation value.
 
<< 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.>>
As with mamy unprotected natural fibers, they eventually decompose and stink 
and become worthless as insulation.
 
<<Straw bales are heavy, they weigh anywhere from 65 to 80 lbs each. 
 You're talking about an awful lot of work.>>
That is true, but I think that lot's of hard work is what some people are 
willing to give in exchange for not having to avoiding dealing with 
commercial establishments and products.
 
<< 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.>>
Or, couldn't you say, the homes in some climates benefit from insulation from 
both hot and cold weather.
 
<< 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.>>
Is it BEST if it suits you, or BEST because of most economical?
 
<< 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.>>
Yes, dirt and rock are take a lot of energy to move them about.
 
<< 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.>>
As cob is earth bound with straw, why would it not make a good berm?
 
<< Again we're talking a fair amount of heavy excavation, again its not
 something everyone wants to live in.>>
Didn't we cover this already?
 
<< 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.>>
Because of which factors?

<<  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.>>
A way to check the thickness discussed years back would be to look at copies 
of the records of discussions held then.
 
<< 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?>>
Seems as if this would be a good time to ask the guy from Devon.
 
<< 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.>>
And that guy who is going to be satisfied needs some facts to work with.  If 
it is true that four inces of cobb insulates to about R one, here is what it 
would take to build a cobb equivalent of my house in Minneapolis, MN.  My 
walls have 7 inches of fiberglass, so the cobb equivalent would have to be 44 
inches thick.  This would not allow much view out of my biggest windows which 
are 60 inches wide.  And the sun would only spend a little while looking at 
my whole 60 inch window, so from cobb I would have to reduce my expectation 
of passive solar gain in the winter by more than half, I would guess.  And 
how many feet of earth would it take to equal the 12 inches of fiberglass in 
my attic?  Looks like about 76 inches thick (6 feet, 4 inches).  I don't 
think I could afford to build a house strong enough to hold up that much cobb 
on the roof.  And I don't want to think about the waterproofing I might have 
to do in the roof, and even less about the thought of repairing a roof leak.  
I wonder how the costs (excavation, shoring, heating & cooling) would compare 
between building a berm that went up the back and right up over the top of 
the house, and digging into the side of an existing hill or cliff or bank?  
Earth sheltering (which is what I described above) was popular in the 1970's, 
and I have made the assumption that earth sheltering was replaced by 
superinsulation because it was cheaper to build and heat and cool and 
maintain.  Does someone have the facts behind the change in popularity from 
earth sheltering to superinsulation?

<< 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 makes post and beam framing, and straw bale walls covered inside and out 
with some durable coating, look pretty good, even if you have to do something 
special to keep the bottom of the bottom row of bales dry.
 
<< 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>)>>
I hauled a few of those 75 and 80 pound straw bales for a neighbor when I was 
in high school, and I thought it was going to tear my arms off.  I went 
looking for hay bales to handle, which at 40 pounds or so, I could toss 
(after handling a few straw bales).
 
<< 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.>>
It has strong appeal to me to handle the materials that my house is made from 
just once, at the time they are installed.
 
<< 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.>>
I vote for a big roof overhang, because I know what it feels like to sit in 
the shade on a hot day.  And if I can feel it, I'll bet the house can too.
 
<< 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.>>
Are you telling me that mice and other little critters don't like to live in 
straw?  That is a surprise to me.  If so, what factor keeps them out?  Do 
they get it down their neck?  Oh, I'll bet you are talking about straw bales 
that are covered with a cement-like coating.
 
<< And you don't need to worry about the kids climbing the stacked bales
 and knocking them down.>>
Amen.
 
<< 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.>>
Yup.  What does the jargon term/acronym "YMMV" mean?
 
<< 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>>
As governent(s)grow, and nice land to live on becomes more scarce, it is 
fairly certain that codes will soon cover most, if not all, the U.S.

Don Negard in Hot Springs, SD