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We're redoing the finishes in a half bath, early 70's construction in NE US. I'm putting in new window trim, while I had it off I planned to add spray foam insulation around the window. This is a very leaky window, most winters I put on seal n peal and a shrink fit film to reduce the draft.

Trim is off, the gap between the drywall and window is tiny in most spots. I don't think I can get the spray foam in there effectively.

Do you think its better to:
-cut out ~1//4" of drywall all around so I can foam
-drill every 4" - 6" and insert the foam gun tip in the hole, hoping to get full perimeter coverage
-abandon spray foam and just silicone around the perimeter. No R value but at least it will stop the infiltration
-any other ideas?

We're planning to replace all the windows in the house in 2-3 years, FYI, in case any solution is better or worse with future window removal in mind.

Thanks for any advice.


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Agreed, locate the real gap, the drywall is easy to cut back.

I did the drill routine on one where the window frame was too close to the rough opening, drilled about every 2", and the fill was good. I used a zero expansion foam. As it turned out I also replaced that window the following year so saw the fill at that time.

As for the two functions, air sealing and insulation, the air sealing is by far the higher priority. Even the old method of carefully filling with some fiberglass insulation would have worked if they had sealed the gap to stop the air leakage. Today foam is popular because it does both in one shot.

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