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GBlist: Re: SB: an interesting moisture snippet
At 05:49 AM 5/4/97 -0400, you wrote:
>This is a part of a post from the greenbuilding list that I thought might
>have some significance to this list. It reinforces one of my pet
>theories about moisture in bale walls, that it is their capacity to store
>large amounts of moisture and give it back, similar to the way wood
>framing in walls does through the seasons, that explains the inexplicable
>ability of the walls to survive in high moisture areas. Anyway, have at
>Begin copied message:
>Date: Sat, 03 May 1997 16:14:20 -0500
>Subject: GBlist: Dense pack and diffusion
>I still have a retrofit question:
>How does one protect a blown in insulation from water vapor migration?
>Is vapor barrior paint the only path?
>I answer a lot of letters on weatherization and generally pays to start
>out with basics.
>Invasive examination of a zillion houses that have had cellulose dense
>packed (DP) into their old walls, has shown no moisture troubles in even
>the most severe climates (wet and/or cold). It's just a super process.
>Here's why: consensation in walls requires 4 things. A large resevoir of
>water vapor, a path, a motivation, and a cold surface. Generally,
>weatherization contractors clean up the water problems before insulating
>because they know the problems in tight, wet houses. DP effectively cuts
>off the path for water vapor between the warm living areas and the cold
>exterior wall surface. We also balance and seal duct systems so that
>mechanical pressurization is eliminated as a motivating force.
>So while we can't eliminate the cold surface, we can to a good job at
>eliminating all the other factors that contibute to condensation
>building failures associtated with retofit insulation.
>But there's something else that I generally don't mention because it is
>too complicated for most novices. It's the *huge* moisture storage
>potential that DP imparts to a wall assembly. Building scientists agree
>that they cannot accurately model the moisture content of a wall system
>without accounting for storage potential and, of course, more is better.
>Well, DP provides the most, and this has been demonstrated to be a big
>factor in protecting the walls and building durability into the finish
>systems. Houses insulated in the '20s with cellulose in Saskatuan
>(12,000 DD) had perfectly preserved wall assembles when studied in
>the late '70s during demolition. It is the only insulation material that
>has a this kind of track record, vapor diffusion barriers (VDB) or not.
>And speaking of VDBs, they are generally considered useless at best and
>destructive at worse. Special paint is silly and completely undesirable
>(along with gloss paint and vinyl wall paper) in the South. Diffusion
>has been known to be a second order moisture problem since 1950. Now it
>is recognized as a non-issue. VDBs in the form of paint and poly sheet
>do not contibute to the pressure boundary needed to exclude convecting
>water vapor from wall cavities. So we don't use them in new construction
>and don't loose any sleep from their absense in retrofits.
>end copied message
>Development Center for Appropriate Technology (DCAT)
>PO Box 41144
>Tucson, Arizona 85717
>Note new fax number
>(520) 624-6628 phone
>(520) 798-3701 fax
>Very interesting post, on a first scan it appears that moisture is not a
problem even in cold climates.This confirms my exp. with cold climate wood
burning where a large amount of outdoor air is required for combustion and
chimney suction. I brought in theair quite close to the stove directly from
the outside and yet i saw the humidity in the house drop as soon as cold
and thus relatively dry conditions prevail.My airtight house did not vent
any humidity- instead we distribute the humidity all over, vent the clothes
dryer inside if not hanging them to dry, etc Occasionally i would see a
momentary iceflower on the glass of my site built double unsealed glass-
after you open the bathroom door you notce an amazingly fast spread of
condensation first down and very quickly into the furthest corner.
it is amazing how moisture creeps into anything and it diffuses all over..
I had an occasional water drip problem when ice against the roof would melt
during mild weather-a tiny crack against the chimney caused condensation
and ice build-up. it is in such ceiling and attic places that miosture can
do damage to strawbales as ice can cause large amounts of meltwater to drip
into one spot on a bale.On the other hand, any house with single glass
would grab any moisture and lock it up as ice on the windows and cause it
to be out of the airmass .untill weather warms up and the ice melts and
Now to the reason for my post:
You mention that you first deal with the moisture problem by "DP"
it blocks the path of the moisture.What is this magic wand? can i have
some? And what do you think of mixing latex paint with sand and clay as a
finish adobe coat on interior strawbale? would exterior latex be necessary?
iplan to run some tests through next year by leaving some bales out to test
these compounds. I see it s a way to recycle leftover paint and have a
little business.Thanx for your opininion and do you think one can
hammermill any paper and or fiber and or styrofoam (white) into a loose
blow in recycled insulation? I had enercon recycled paper blown into my
double stud 8" northwall and it worked well altho there was some bulging on
the interior as i used 1/8" recycled sawdust panelling and it was not stiff
enough so i recommend nailing strapping up on the inside
and i used continuous airtight 4 mil poly, the sticky goop and all.
It was an investment that paid off ever since.The plastic may not be
necessary to keep out moisture but careful airtight detailing keeps in the
warm air and produces a higher relative humidity in our conditioned space.
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