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

[Shody Ryon]

> 
>      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.
Hi,
Assuming dry earth has about ½ the thermal storage
capacity of water and some degree of R value,
all-be-it rather low, perimeter rigid insulation
buried horizontally underground out side the
structure, as opposed to installing it vertically on
the exterior of the foundation, will yield more
thermal mass, if I understand this concept.

http://greenershelter.org/index.php?pg=3

So I propose back filling the excavated trench dug to
erect the foundation walls with 3/4” drain gravel in
case of membrane failure and covering it with rigid
insulation then rubber then soil for flowers. So the
perimeter is underground exterior to the insulation
envelope.
>      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.

That is the common conception, I am sure. Lets take a
look at the vaulted ceilings that have rigid
insulation without any air space. Why don't they have
an air space? For some reason they are exempt from the
rule other ceilings have of needing to be vented. All
other ceilings are supposed to have ventilation, as
far as I know. Dense packed cellulose, if truly
uniformly packed, should stop air convection inside of
the wall and if so, should stop the source of
condensation, correct? 
 
>      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.

This is what really gets me confused. Isn't gypsum
board  air tight? That is, if the wall penetrations
like electrical boxes are sealed on the inside of the
box as well as on the outside? They used to call the
first coat of mud and tape, “fire taping” because fire
was positively slowed by this process. Assuming the
wall is sealed with either the gypsum board or the
vapor barrier, am I to believe moisture will not enter
the joist bay from the exterior where there is no
vapor barrier? If there is a vapor barrier on both the
interior and exterior, does that mean the inside of
the wall will have less vapor inside than the climate
supplies to the general area? If so, how and why is
that the case? If not, the whole vapor barrier
argument is founded on faulty logic, or what am I
missing?
Thanks to whomever wishes to enlighten me.
Cheers,
Shody


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