[Cob] Other components: How bad is Tyvek?

[Amanda Peck]

I don't quite visualize what the order of layers is there.

Can you just think, "the original inhabitants of this cabin probably just 
lived by the fire in the winter, unless they had some sort of powerful 
blanket/down/fur to sleep under, we can do the same!"  (My dogs and I think 
anything above freezing is pretty good sleeping.  But we do have the 
powerful down.)

I'd consider that styrofoam stuff fastened to rafters/roof sheathing/purlins 
that keeps ventilation where you want it--the underside of the roof, below 
that insulation, and below that put a ceiling.  If I've got what you're 
doing right.  Even before I heard that the Feng Shui people hated exposed 
beams/rafters directly above sleeping people, I wasn't a big fan of them.  
Probably partly because I once worked for a construction company that put 
faux exposed beams in to try to give some class to their awful houses.  I 
don't really think it did.


David Atmoweg wrote:
Greetings, everybody-

A while ago the combination of light clay straw and wool came up.  I was 
happy to report that there's finally a place in North America that offers 
wool as
insulation.  After two particularly tough winters, we're a little 
disillusioned.
We're working on a two-hundred year old cabin in the Catskills, and used 
light clay straw for the walls, with which we're quite happy.  We haven't 
even plastered
over it because it's so lovely by itself.  We tried to make panels of light 
straw clay to fill our rafter spaces, but the stuff proved awfully heavy to 
try to hang, and all
the spaces are different widths and we ended up using wool.
Now, the light straw clay doesn't let a lick of air through, so far as we 
can tell, but it takes a long time to warm it up.  Its thermal mass seems to 
be working
more as a heat-sink than a storage mass when it's below zero outside, and 
I'm wondering if we should seal it better from without.  The wool, 
meanwhile, isn't
living up to its R-value because this is a leaky, gappy old structure and 
wool batting doesn't halt a breeze.  The upshot is we have at times a fifty 
Fahrenheit
degree temperature differential between the floor downstairs and the air in 
the rafters.
We wanted to cover the wool upstairs with burlap, which is cheap and 
low-impact and would look like a good compliment to the light clay 
downstairs, but we
begin to think we need a real barrier up there.  Our woodstove is churning 
out the BTUs and they're getting away from us.  So the question is, do we 
buy three
rolls of Tyvek, trap the wool upstairs and back the light-clay downstairs?  
We need to maintain some moisture flow for the light clay, of course, but we 
appear to
be living in a seive now.  Is Tyvek made in a toxic, wasteful process?  What 
benign substance can we seal this place up with?  I tried to infuse a sheet 
of burlap
with beeswax, but it's just too coarse.  Canvas might work that way, but 
it's expensive and heavy.
Somebody out there has the answer, I'm sure...

-d.

http://www.flamingbunny.org
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