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drain planes

karnofsky's picture

drain planes (post #204456)

I'm working with a general contractor who is building my house.  I also work as a builder.  Our wall system is drywall, 2x6 spruce, 1/2"cdx, 4" XPS, ?, sheathing, white cedar shingles treated with bleaching oil.  My builder wanted to put tyvek over the inner sheathing, which I talked him out of.  He also would like to create a drain plane between the foam and the outer layer of sheathing, and then use felt or building wrap under the cedar.  I'm wondering if we could skip the furring over the foam and then use a draining housewrap, (which I've never used, and it's not generally available in this area)between the sheathing and the shingle back.  Any thoughts or advice?

more info (post #204456, reply #1 of 1)

I was interrupted putting the query together.  We're in Downeast Maine, right on the water.  I'm putting in radiant heat and trying for a super insulated building.  We've talked about doing a thin layer of spray foam in the stud bays, under the roof, and rim areas but I'm not sure I can afford it.  I got a good price on the XPS board so there will be 4" everywhere in the outer layer of the walls.  Another area of concern is ice damming with the unvented roof.  Building Science recommends some sort of venting under the shingles, not for heat, but because the insulating value of the snow load can cause ice dams.  I'm not sure if that would be a factor for me or not. I don't really understand what he was getting at.  The roof is a 6 pitch, but the snow storms have generally blown over the house (this is a rebuild after a fire), we haven't had big accumulations on the roof.  Anyway, thanks in advance for any input.