[Strawbale] Frost Heave-basement/cob

[Speireag Alden]

On 2007, Nov 26, at 20:22, GuyW wrote:

> gee...millions of dollars has changed hands in SoCal over vapor- 
> emissions
> thru concrete....There are standard sodium chloride dome tests to  
> quantify
> vapor transmission thru concrete...guess not, tho...

Looking in the ASHRAE Handbook, it appears that concrete is 3.2 perms  
per inch of thickness, which means that a quality four-inch slab is  
about .8 perms.  Anything under 1 perm is a vapor barrier.

An eight-inch concrete wall could be .4 perms.

So, yes, concrete can be a vapor barrier.

I over-stated when I said that you had to intend it to make it vapor  
permeable.  Poor quality concrete, or old concrete which has been  
stressed, can be more permeable.

Getting back to the original question, though:  if you have a  
basement wall with some soil moisture outside of it, and you generate  
moisture inside the house, and you insulate on the inside of the  
basement wall, you can expect condensation behind the insulation, and  
subsequent mold problems.

-Speireag.