Cob: RE: Insulation

[Sojourner]

Otherfish at aol.com wrote:
> 
> <<Anyone done this?  What kind of wall thicknesses were used?  I imagine
> it might have to be fairly large for stability of each wall - 1-2 feet
> thick each?  And how much airspace?>>
> 
> IMHO this is one of the less estute ideas to be suggested
> on the list - I mean, its enough expense & work to build
> ONE cob wall - why build two simply to insulate your building
< - bad idea !!!!!!!

Because if you're living in the north where it gets COLD you MIGHT want
to stay warm.  Well, maybe not you, but most of us.

Cob is not quite as bad as stone, from what I've been told, but some
insulation is still indicated - at least for those of us who would like
to stay warm without having to burn down the whole forest over winter.

BTW, the word is "astute".

> <<Would packing the airspace with straw help or hinder?>>
> 
> It would help - straw is VERY good insulation
> 

> - BUT at the risk of being pedantic - this double cob wall idea
> is really too dumb to even consider

Ummm, I don't think you know what the word means.  Do you realize you
just called yourself "narrow, stodgy, unimaginative, pedestrian"?  I
would have to agree with you however - you are being pedantic.

The only meaning of that word you have not fulfilled is the one about
being ostentatiously learned.

> - OHHHH how opinionated .......!!!!!

At least you're honest.

> <<I want to build a structure (or perhaps even structures in
> the north-east somewhere (NY or New England), but I have these
> nagging concerns that I will just end up building a chilly
> vault (at least in the winter).  >>

I'm with you.  I'd say stone has a lot more thermal mass than a cob wall
- have you ever been in a stone house in the north in winter?  I have -
a "chilly vault" doesn't BEGIN to describe it.

Cob has more insulative properties than stone, but not enough to make a
difference as far as I'm concerned.  If you build the walls 3 or 4'
thick, that might do it without having to go to a double wall cavity. 
I've seen figures bandied about on this list for R values of .25/inch to
1/inch - I suspect the lower figure is more accurate.  So a 4' thick cob
wall would give you an R12.  It's hard to say what the insulative
properties of cob are because it varies so widely from one site to
another on just what the actual stuff going into it is.

I'd go with a double wall myself.  For sawdust, a foot wide cavity would
give you tons of insulative capacity, I don't know about straw.  If
there's a sawmill anywhere near you you should be able to get all the
sawdust you can haul away for free.  It will settle over time - you
might want to give yourself a way to get back in there in a couple years
and add sawdust, if you're putting it in loose.

> Not if you make it passive solar with some sort of heating backup
> (wood burning is pretty low tech & (dare I use the s word)
> ssssustainable ).

Wood burning is actually sustainable only if it is practiced only by a
small percentage of the population on enough land to maintain their own
personal woodlots (and I do mean maintain - NOT just cut 'n clear until
you run out of wood).

Coppicing might work well with a masonry stove, but coppiced wood is not
so good for the typical wood stove - has a high potential for increased
creosote buildup in your chimney.

If everybody in the country started burning wood the pollution would not
only be incredible, we would run through every burnable stick quicker 'n
you could say "jack flash".

What's "sustainable" on a small scale is not always "sustainable" on a
large scale.

Of course, you could say that our current population level is itself
"not sustainable".  But I'm not planning on doing anything to reduce the
population level to one I think IS "sustainable", myself.

> Think simple - put a winter coat of bales around the cold side
> of your building

In New England and New York, that would be all four sides, really. 
Well, maybe he could skip the south side - depends on how much sun he
typically get in the winter.  Some places are pretty much overcast all
winter and you're not going to get much solar gain when its cloudy. 
Some places aren't.  Not knowing which sort he has to work with, it
behooves you to cut the guy some slack.  One solution doesn't work for
everybody - if it did, we'd all be living in stick-framed cubicles in
town, and we wouldn't be having this conversation at all.

If you want straw bale insulation, just build a straw bale house - and
plaster it over with cob.  A perfectly acceptable solution, and in a
cold northern climate, probably a better housing solution than straight
cob.  IMHO.  YMMV, and obviously does.

I know someone who was planning on building a double wall and insulating
the center.  I don't think its a "dumb idea" - what's a "dumb idea" in
my opinion is ignoring the question of insulation in a climate like
that.  I know someone posted to the list about some guy who thinks his
northern cob home is warm enough unheated to be comfortable in in the
winter as long as you're wearing a coat and gloves - well, that's not
exactly my idea of "comfort".  An unheated cob house in the north is
going to end up being just about the same temp as it is outside -
thermal mass and "solarizing" notwithstanding.

Like I said, sometimes its cloudy.  Sometimes it SNOWS (*gasp*). 
Sometimes you might like to keep warm in a sustainable fashion - and
that includes conserving your own energy when cutting and splitting all
that "sustainable" wood fuel.  Which you DON'T want to have to do in the
middle of winter when you've run out of wood trying to keep your
uninsulated cob house warm.  Green wood isn't a whole lot of fun to
burn, either.  Burns smoky and not as hot.

I'm from Ohio, and we virtually never see the sun all winter. 
Solarizing would only make me too hot in the summer, wouldn't help at
all in the winter.  And it doesn't get near as cold where I'm from as it
does in New England.  Upstate New York can get preeettty durn chilly -
they say they have 2 seasons there.  9 months of winter, and 3 months of
Bad Sledding.

I say go for the insulation idea, its not a dumb idea.  If you use straw
or sawdust between the two walls, make sure you protect it from the
possibility of wicking moisture up through the bottom - maybe a foot
thick layer of plastic peanuts all around, covered with a thick layer of
plastic, then the straw or sawdust on top of that.

I don't know about straw, but from another list I'm on I have found out
that the sawdust idea (for insulation) works just fine, and you can
treat it with boric acid (10% by weight) to cut down on fire hazards and
reduce any potential insect problems from not much to nil.

Good luck, hope you find a truly sustainable way to keep warm in the
way-to-cold for me climate you're looking at.

Holly ;-D