OSB sheathing touching foundation wall: Should I be cutting a 1/8-1/4″ slot to prevent direct contact and wicking?
Construction is 2×6 wall, 7/16 OSB, 2 inch EPS foam (high perm), house wrap, 3/4″ rain screen and siding.
Currently exterior walls are up, with a standard foam sill plate gasket and the 7/16 OSB. I am wondering if the OSB in direct contact with the concrete foundation wall will be an issue when the whole wall is completed. Drainage plane for the house wrap is right at the edge of the foundation wall, and rain screen/siding actually hangs off the wall 3/4″ + siding thickness.
Ideally the framers would have spaced the OSB sheathing of the bottom plate 1/8″ or so, but now the walls are done. Is it worth it to router cut a 1/8″ groove at the bottom of the sheathing to create an air gap? Or will this dry out well when the whole assembly is up and moisture (no pooling water) is the only challenge?
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Replies
Mai tai, manufacturers suggest a 1/8" gap around ALL sides of the sheet for expansion purposes; I suspect 9 out of 10 framers are moving too fast to monitor this carefully, although I've worked with some who place a couple 8p nails as shims. I wouldn't waste my time going back and fixing it. Save that impulse for the really egregious errors by your subs. The top of the foundation undulates enough that the perfectly flat OSB probably only touches here and there anyway. Your rainscreen details keep bulk water away; caulk the joint for extra insurance. If you're planning some kind of protective metal or plastic channel at the bottom of your exterior EPS, maybe that could be caulked to the OSB/concrete interface as well, since your WRB is outboard of that.
Mai Tai,
If you are planning to install 2 inches of EPS and a 3/4-inch rainscreen on the exterior side of the OSB, I wouldn't worry about the OSB touching the concrete. Rain will be dripping off your siding, not your OSB, and the siding drips will be 3 inches outboard of the OSB.
All of that said, your framers should know that it's best if the sill plates overhang the foundation a little bit, to avoid the situation you're describing.