Pre Treated Wood or XPS or FoamSeal

the-tech-guyJanuary 24, 2012

hello all,

I am about 95% complete with insulating my concrete walls with XPS. I was able to glue them but I spent alot of time smoothing out the walls with my Fatmax chisel. Anyway, my next step is framing! My question now is what is the best method for protecting the base wood from rotting? Do I use XPS, or the Owens Corning Foam Seal, or pre treated wood? Ideally I would want the most cost conscious choice however if one is really better than the other I would probably go that route.


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Sill plate gasket is an excellent seal on the rim (foundation to base plate) and in similar wood to wood connections. But it is not a water barrier and should not be used below the base plate. Instead, you can use 6 mil poly, which is available in 9" wide rolls. I prefer using strips of 1" thick XPS, scored and snapped from standard panels. They serve as a barrier to the liquid water, plus raising the base plate above any small floods that may occur. XPS costs more than the poly. I don't use pt bases as I don't like the idea of cutting that inside; the sawdust is not healthy and you have to coat the cut ends of the PT wood.

Owens Corning polyurethane sill plate gasket is designed for use between the foundation and the wooden sill plate to inhibit air infiltration.

    Bookmark   January 24, 2012 at 2:15PM
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Thanks for the reply.
If I did go with the 6 mil poly, do I just cut strips or do you actually wrap the bottom plate with it?

    Bookmark   January 24, 2012 at 2:44PM
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Just roll it out, centre the baseplate and attach it through the poly. It comes in black, which makes it easy to see where you're putting it.

The poly serves as a capillary break, thus preventing the rise of moisture up the concrete and into the wood. Capillary moisture movement has great power; it's what moves water up every tree.

    Bookmark   January 24, 2012 at 4:43PM
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I had some time off from my basement project and now I am starting up again. I left off cutting XPS to use as a baseplate but that got time consuming so I am looking at PT wood. I called around the local big box stores and they are saying now PT wood is safe to use. (Hmmm?) What is safe enough to use? Home Depot sells a green wood called Top Choice and MCA MicroPro. I also read about Bluwood and Timbersil. Any recommendations?

    Bookmark   December 13, 2012 at 12:33PM
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Any CA (copper azole) or ACQ (Alkaline Copper Quat) pressure treated wood is considered relatively benign as long as you don't burn it, which releases the toxic chemicals into the environment. Still, use masks and gloves when handling it.

The active ingredient in Bluwood is chlorothalonil, a potential human carcinogen.

Still, a lot easier to use the XPS. Just lay the foamboards on the floor or across a couple of sawhorses with a layer of ply or OSB scrap underneath. Then score the boards with a razor knife and snap off on the edge of the ply or a 2"x whatever. No need for precision. Takes about a minute a cut.

    Bookmark   December 13, 2012 at 1:22PM
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