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Flashing for siding with no air barrier?

Posted by katdip (My Page) on
Wed, Feb 27, 08 at 19:30

I want to renovate the bump out on my 1916 house to make it a usable breakfast nook. It is roughly 8x12, and I will be replacing 4 windows, adding an exterior door to a new deck, and insulating so it can be used year round. The outside siding is 1"x8" redwood shiplap, nailed directly to the studs. It is generally in good shape, except where the crappy windows leaked. I want to know 1) how to flash the new windows and doors so I avoid future leaks and 2) whether I should try and put an air/water barrier on the inside before insulation. I am not planning on removing all the siding, just some around the windows and doors, and replacing some rotten pieces.

My one thought is to directly spray isocyanate foam on the inside of the siding, to serve as both an air and water barrier. Anyone see problems with this?

Follow-Up Postings:

RE: Flashing for siding with no air barrier?

Foam is probably the easiest air-sealing option you have, IMO. Don't know the water barrier difference between open and closed cell foam, so someone may chime in on this or need to be researched by you.

Wonder if you should coat or cover the inside of the redwood siding? My thinking is that if some ever needs to be replaced, pulling the board off might tear/pull the foam insulation out. Pieces of Tyvek/Typar in each stud bay would suffice, then foam the cavities. Could be a pain of a job on a large home, but a small nook would be a DIY option. Just some thoughts.

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