XPS basement walls

Old 01-08-15, 03:48 PM
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XPS basement walls

Just starting on finishing part of a painted concrete block wall dry basement. My plans are to glue 2" XPS board R10 to the exterior block walls then frame in front of the XPS with 2x4 studs and finish with drywall. I do not plan to use any additional fiberglass insulation in the exterior stud walls, but will use fiberglass with vapor barrier on the interior walls between unfinished and finished side of basement.

Since none of the walls are load bearing, I would like to put some non-wood spacers (1/4") between bottom sill 2x4 and the concrete floor to permit any water that might ever enter get to the drain without wicking through the wood sill and to keep the wood off the floor.

Any recommendations for what I am planning to do, including what to use for spacers?

Old 01-08-15, 04:57 PM
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Vapor barriers have no place in a basement, IMO. If you are using kraft faced insulation on your interior walls, that's probably ok. (for the sake of stapling it up) My suggestion would be to use unfaced insulation on exterior walls and be darn sure you airseal all the XPS joints with a compatible tape. Leave a gap at the floor and foam it. If you place foam against the rim, air seal the edges with foam, and lay a piece down between joists (flush with the bottom of the joists) so that wall foam will meet ceiling foam... and tape that joint. Glue is probably a waste of time and money, since something's going to have to hold it back into the glue anyway... I'd probably predrill a small hole with a masonry bit and hold it to the block with just enough cap nails or fluted masonry nails so that it won't fall down. (hopefully, just one at each corner) Once the wall is framed in front of it, it won't be going anywhere.

A couple coats of latex paint is usually all the vapor retardant you need.

For your sill plate shims, I'd probably just cut some 1/4" treated wood shims. But if you are stuck on using non-wood, PVC boards or any type of solid composite decking ripped down to size on a table saw would be fine. HD sells Azek, Menards has Certainteed PVC... Lowes has Royal PVC I believe.

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