Cob: [Fwd: Re: insulation]

[Darel Henman]

Andrea,
  some comments interspersed with yours.

andrea arnold wrote:
> then receiving her reply about cob only being used in warmer climates, etc.
She was wrong.  They are used in cold climates.   But, not extremely
cold and prolonged freezing,
cloudy climates.    (Anybody know what the middle east earthen houses
are made of?  Rammed earth?)

 
> I've read several books on cob building and none of them have ever mentioned much on insulating, other
> than that you should make a cob mix with a higher ration of straw in it for better insulating
> properties.
There is a limit to how much straw can be used and this depends on the
character of your clay soil as well.  If you add too much straw your
walls won't be strong enough to bear up a roof, and it won't be cob
anymore it would be more like the "light clay" mix used for non-bearing
walls and uses a form to shape it.


> I know people use cob in cold climates. I had always been under the impression that 2 foot
> thick exterior walls were insulating enough by shear mass.
Not in all cases.  The mass will carry you over well, but it will lose
heat.  It needs a source of heat to keep it warm.   Depending on your
climate for example, solar radiation and heat energy through windows may
be sufficient to carry you over.  But, continued cloudy spell for two
weeks could easily deplete any heat in the walls.   It would then take a
lot of energy to get the walls up to a comfortable temperature again.  
The heat will seep out of the walls in both directions, inside and out. 
More of it will go outside during the winter because it has the greatest
thermal gradient (its colder outside).

Also note, that historically they didn't insulate the walls, doesn't
mean that its a good idea.  If you are in a cold climate, it is wise to
insulate at least the north wall.  This can be done in several ways. 
Some people simply put a shed or storage on that side as a buffer. 
Others insulate it.   

Think about how and where, the heat will be leaving you house.  Miniize
it as much as possible.

> Everything I've read on passive solar design says how good cob is to absorb heat during the day
> from the sun to then give it off at night to warm your house.

Yes.  But it is a very general statement.  For example you must have
heat during the day, as you noted above.
Cob will perform magnificently in the summer for my hometown for example
when the day is hot and the nights are cold.   But, for the winter time
you have to consider the longest cloudy period, when no solar energy get
into your house.  It wouldn't hurt to consider supplemental heat in your
design and then add it later if needed.

> 
> I am looking to build a house next year in northeastern Pennsylvania.  Winter nights can be in
> the low teens and single digits.  But I know there are
> cob homes in PA, NY, MA, etc.  There's a cob "company"
> in Colorado and another one in Vermont.  Plenty of
> people have built in cold areas and this is the first
> I have heard of someone having to put in layers of
> insulation.  So I'm still a bit puzzled by it.
This was probably necessary in areas like northern England, Scotland
where there are prolonged periods of cold cloudy days.  And at any event
it would be better to insulate it on the outside, notably the north,
east and west sides which won't get solar energy anyway, but will suck
out heat.  Insulating on the outside here, keeps the thermal mass energy
storage inside where you need it and can use it.  

> 
> I was also wondering if layered walls were then strong enough to hold up the roof.
They can be made so.

> A while back in the conversation, Marlin had mentioned the cob walls were
> two 6" thick walls with a layer in the middle.  Would
> a thicker solid cob wall be stronger/safer?

I would definiteyly, say that a thicker monolithic cob wall would be
stronger. 

> Anyway, I am new to all of this.  I'm 28, and after 10 years of wasting money on rent, this will be my first home.  I'm currently living in WA, but plan to move
> back to my native PA to build.

Material issue: Check out the soil there for clay content and charater. 



> I've also been
> volunteering on weekends with a natural builder in my
> area.  I've learned some basic carpentry and have been
> helping him insulate a regular wood framed house with
> light straw clay in the walls. 
Good idea. Sounds like fun.  Note, I also heard of using rices husks,
instead of straw in a mixture for insulation.  And also just carbonized
rice husks.  Carbonized (scorched black) so pests wouldn'T be attracted
to it.

> I plan to attend a cob workshop this summer, and am now wondering if the way
> cob is built out here in the Northwest will work in the Northeast.
It should.  Remember that cob as they know it in the Northwest, started
in England and Europe of a thousand years ago.  The town of Devon in
Great Britan still has 800 year old cob houses about.

See:  http://www.devon-calling.com/culture.htm#Cob Walls

Here's a good cob article:  
http://www.periodproperty.co.uk/article004.htm

Regards,
 darel

> 
> I was interested in building with cob because with
> what I've read, cob is overall the cheapest and the
> easiest- as far as skill level-  method of natural
> building for a beginner owner/builder.  The longer I
> stay on this cob email list the more complicated it
> seems to be getting!  Any advice from you is much
> appreciated.
> 
> Thanks,
> 
> Andrea Arnold
> 
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