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Draftproofing a Window

The answer is usually in the gap

Ask This Old House Crew
Photo by Matt Kalinowski

I'm having a problem with drafts coming from behind the interior trim around a fairly new replacement window. To avoid disturbing the new stained trim, I'm thinking of drilling holes through the exterior window trim and injecting foam insulation. Would that work?
— Nancy, Shoemakersville, PA


Tom Silva replies: You have a common problem that usually arises when a window installer doesn't bother to insulate the fairly small gaps between the rough opening and the window frame.
You do need to plug those gaps to stop the drafts, but I foresee nothing but trouble with your method. First, you'd have no idea whether the foam was adequately filling the area between the window frame and the sill. Also, you'd run the risk of injecting too much foam and bowing the trim or the jamb, which would make moving the sash difficult. Either way, you'd still have to patch the holes in your trim and touch up the patches with paint.
The better way to handle this job is to remove the interior trim by prying it off the wall, nails and all. A couple of Japanese-style pry bars with thin, wide "tails" are perfect for this purpose. Then use nippers to pull the nails through the back side of the trim. (Pounding nails back out the same way they went in would almost certainly damage the wood surface.) Once all the trim is off, you can easily seal any gaps around the window with low-expanding foam.
After reinstalling the trim, countersink the nails with a nailset and fill the heads with putty matched to the color of the stain. You may have to blend putties to get a good match, but with a little care nobody will ever see your work.


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