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XPS under radiant floor? open vs. closed-cell spray foam walls?

Posted by infohound2006 (My Page) on
Mon, May 11, 09 at 5:13

Hi folks,

I have two important questions regarding insulation for our basement which will be our rec / media room.

1. Should we insulate the concrete floor by extruded polystyrene (XPS) below our radiant heating panels? (the current plan is a thin poly sheet, Rehau Raupanel, + floating engineered wood).

2. We want to foam the cold concrete-block walls, and our GC is recommending open-cell spray foam rather than closed-cell foam, "so that the concrete can dry to the inside". (Now that I've read Building Science articles, I'd have gone for XPS panels there too, but our GC has already built a framework of metal studs in front of the concrete, and Paraseal waterproofing memmbrane on the outside)

I know that the cc is a vapor retarder, not a barrier, but I'm especially skeptical of the open-cell foam below-ground because it can absorb moisture. Am I right? Can someone point me to a Building Science or other respectable reference?

3. For sound-control of the ceiling, what are the relative costs of QuietRock, open-cell foam, and ???. (remember, this will be a pool / media room)


PS. We're in the high-labor-cost SF Bay Area.

Follow-Up Postings:

RE: XPS under radiant floor? open vs. closed-cell spray foam wa

According to Dr. Joe, either type of foam is acceptable.

See "Understanding Foundations" (See Link) p. 6 .

I prefer cc foam because its higher R Value means it uses less space. Also, when applied on cold surfaces, the oc foam shrinks back.

Here is a link that might be useful: Understanding Foundations

RE: XPS under radiant floor? followup

For soundproofing, use soundproofing materials--either constrained layer damping drywall, such as Quietrock brand or multiple drywall layers and Green Glue. Before the constrained layer drywall was invented, I used multiple layers on resilient channel. Lots of labour that can be easily short-circuited by just one wrong fastener, research shows.

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