permaculture

["Eugene F. Monaco" <EFMonaco@compuserve.com>]

There is a strawbale discussion group that has beaten this moisture issue
to death, and then some.  While there are some experts doing lab testing of
various wall sections, with and without vapor barriers, there seems to be
three schools of thought.

First, let me say that there are examples of 100-plus year old straw bale
homes in humid climates, particularly in the UK where it was supossedly
first contemplated. Sstraw bale and it's sister, cob, which is straw mixed
with clay and sand, generally does okay if it's stucco'd, and (read well)
sheltered from rains via an overhang.  If you keep the rain off the wall
the straw will tend to stay dry.   Fungi thrives in moist, acidic
condidtions (forest floor), and the use of lime-based stucco along with low
moisture, tends to cause an alkyline condidtion which keeps fungal rot
within tolerable levels; tolerable being 30 to 60 years life span, note the
pyramids were not made of straw bale, also note that most conventional
apartment houses are only designed for 30 to 50 year life span.

So the three schools of thought on vapor barriers are as follows:

First, is the use of a vapor barrier as Dan H. explained, on the humid side
of things to keep the moisture out of the wall.  Think of your hot steamy
kitchen and bathroom.  There you'd want it on the inside of the wall.  But
what about days when its dry inside (maybe a fire going) and it's humid
outside.  Then it seems as if you'd want the VB on the ouside.  Most
conventional thinking and construction practices put it on the outside;
they even shrinkwrap the house with a product called Tyvec.  In my
experience as a disaster recovery consultant, I've seen rotted walls
(conventional studs and drywall) at guess where?  The bathrooms and
kitchens.  If it were me I'd put a double VB at the bathroom and kitchen
(inside and out) to keep the moisture out of the wall.  But we all know the
moisture migrates doesn't it?

So that leads to the second school of thought which says, install a VB on
the outside as well as the inside. Slick but expensive.  Also, as anyone
who has dealt with stucco in Florida knows, when it rains, the stucco gets
wet, then it dries.  But in Florida they're using stucco over concrete
block so the block doesn't rot, but it can get dank in there unless you
have AC.  There is a product, genererically called EIFS (Exterior
Insulation Finish System), also known as Dryvitt, or Sto, that has as it's
final layer, a waterproof final coat which beads off the water and doesn't
get wet.  These layers of 'mud' are applied over exterior rigid foam
insulation, held together by a fiberglass mesh.  It allows you to shape
things and get architectural detail which is why it's popular.  The final
coat being waterproof is one of it's claims to fame.  Not to be outdone,
the paint industry came up with a product called elsatomeric paint which is
like painting your wall with rubber.  It's elastic, a polymer, easily
patchable and, if you can stomach the toxins produced from the entire paint
industry in general, not a bad product.  It will waterproof the outside; so
there's your exterior VB.  Slap one on the inside of the wall, or just at
the bathroom if you're in a bind, and you've got your double VB wall
section.  The theory is that you just flat out don't let moiture in.  But
you better keep the bales dry during construction.  And of course there are
the leaks.

The final and I think best approach is to forget VB's all together and let
the wall 'breathe'.  Forget plastic VB's, elastomeric paint and the like. 
Just use a lime-based stucco on both sides, and keep the roof overhang in
tact.  The moisture will migrate through the walls and not do all that much
rotting in a reasonable lifespan.  Of course don't try to impress an
up-town yuppie with this system, it might be a little close to the earth
for them.  But it's inexpensive.  I'd still install a VB at the toilet room
if there were showers in there, and design for good ventillation where the
interior humidity was high.

Having said all this, let me close by saying that in general I don't like
straw bale for the eastern US, mainly due to the totally unsustainable
agricultural methods in which the wheat straw is produced.  If you drive
through southern Ohio, and parts of the midwest where they grow this wheat
straw, it is a monocultural nightmare--the most devistated land I've seen
in these parts.  It's difficult to justify purchasing straw from these
farmers.  If one were to grow one's own wheat, organically, or
permaculturally, Fukuoka style, one would want all the biomass to be
returned to the site and mulched, not hauled off as if a surplus to build
houses.  But then again, we're in transition, it's all relative, and there
are trade offs.

Below is subscription information for the strawbale discussion group.

Regards,
Gene Monaco
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
East Tennessee Permaculture  (EFMonaco@compuserve.com)
Herbs, consultations, & training for total health and environmental
sustainability
PO Box 11851, Knoxville, TN  37939      (423) 457-4354
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

*************** Forwarded Message *****************

>Will someone forward me a copy of the instructions for setting Digest
mode,
>signing off, etc.  I deleted the file I had accidently.


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