OSB before Rigid Foam?
I'm planning the renovation of a small (920sf) home in Indiana (Zone 5). The original home is 112 years old, but at some point it there was an addition (yes, it is still only 920 sf). So the original exterior walls have no sub-siding (sheathing) but instead has a very hearty lathe on the interior of the stud wall. The exterior siding and the hearty lathe both have to go. The addition has 1x6 sheathing boards on the exterior of the studs, hung horizontally. We'll be insulating the wall cavity and want to hang rigid foam on the exterior before siding and I want to know if there should be sheathing hung first, such as 4x8 sheats of OSB.
I have these questions:
Is it needed structurally? Many GBA videos show rigid foam going right up on the new construction studs. With such a small house, I'm thinking it might not be required for this reason.
Would the OSB need a water-resistant barrier, such as housewrap, before the rigid foam? Or, is that redundant since the foam will be taped and sealed tightly?
Our wall cavity insulation is currently planned as spray-cellulose, and so I very much want to keep this stuff away from any exterior moisture.
Finally, if I sandwich sheathing between an insulated wall cavity and rigid foam, am I creating wall rot potential?
My contractor and I are game to figure it out, so any advice is appreciated. Thanks!
Posted Dec 19, 2012 8:28 PM ET
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