XPS or No....I noticed this

andrelaplume2September 17, 2008

I have been struggling with weather or not to use XPS. I was in my Dad's 22 year old 4 star energy efficient PPL home with finished basement an noticed that his poured concrete walls were insulated as follows:

Pourced Concrete Wall, Plastic Sheet directly against that, white 1/2" styrafoam against that. Thats it! He does have a section drywalled. I assume they just studded in front of the foam. I found the plastic in between the foam and concrete interesting.

Of course the styrafoam of 22 years ago is likely different than the XPS of today.

It seems the methods are always changing.

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The white foam is probably expanded polystyrene (EPS) like the stuff in coffee cups. If they had omitted the plastic it would have been perfect, though lacking in R-value. If the plastic runs right to the top, there's no way for the wall to dry either way. At least, the foam should be essentially undamaged by any condensing vapour on either side of the plastic. Nowadays Fire/Building Codes require the foam to be covered by a 15-minute thermal barrier.

Twenty years ago, I was using the worst but most common method: fiberglass batts with poly to the inside and often poly against the wall too. But I would run the concrete-side poly down under the drywall, which was cut an inch above the floor. The idea was that any condensing vapour would then run back into the finished space. I learned of that technique somewhere in the "expert" literature of the time.

    Bookmark   September 17, 2008 at 8:41PM
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