[Strawbale] Pressure-treated Wood Foundations ( PWF) (was re: Frost heave)

[Speireag Alden]

Sgrìobh Shody Ryon:

>Thanks for talking the time to give your thoughts. I
>am wondering if I were to back fill with large amounts
>of gravel and cover that with a 2 meter perimeter of
>EPDM rubber sloped at 50mm per meter (I am trying to
>approximate 1/4" per foot) with a termination into a
>slit pipe underground gutter at the outside perimeter
>for water drainage if the rubber and back fill that
>with a foot or so of soil for flowers. I realize I can
>do what ever I want, but I recently have been bias
>against wood foundations and wanted to run through
>this with someone.

     Could you provide more details, Shody?  What are you backfilling? 
What is the perimeter which the EPDM is around?  I'm not able to 
picture what you're asking.

>If a wall is insulated well,
>that is it, has no convection or air movement inside
>of the wall and the insulation absorbs and releases
>moisture well and retains its R value when wet would
>that eliminate the source of moisture.

     The wall construction has nothing to do with the source of 
moisture, only with how it deals with the moisture.

>I am thinking
>of 9 inches of dense packed cellulose, and thinking of
>doing away with a moisture barrier. If it had a
>relatively stable gradient of temperature through the
>insulation wouldn't that eliminate condensation?

     No.  Condensation is not a response to sudden temperature change. 
It is a response to the temperature dropping below the dew point. 
The location of the dew point depends on the amount of water 
suspended in the air.

     So, if you have a wall with no air movement, but no vapor 
barrier, then the moisture (vapor) which is suspended in the house 
air will diffuse through the insulation as vapor, until it reaches 
that point in the wall where the temperature is at the dew point. 
There, the vapor will become liquid water.

     But that's a fantasy wall.  They almost all have some small 
amount of air movement, and I would venture to say that insulated 
stud wall *all* have some small amount of air movement.

     If you're building a wall in a cold climate, put a moisture 
barrier on the inside, and seal all penetrations obsessively.  The 
main way that vapor gets into a wall and condenses is not vapor 
diffusion through solids, but rather, carried on the back of air 
movement through very small cracks and pinholes.

-Speireag.

-- 
A wise man will make haste to forgive, because he knows the true 
value of time, and will not suffer it to pass away in unnecessary 
pain.
--Samuel Johnson, lexicographer (1709-1784)