I had new vinyl triple pane windows installed several years ago. Long story short, the contractor placed the new windows directly on top of the 2x4 (home built in 1951) leaving very little to no space to insulate along the bottom of the window. There are drafts such that the wind literally whistles through. Tried caulking it. At -20 decrees F, the caulk cracked and the wind resumed whistling in. My question: can I drill small holes along the bottom of the window (where it meets the 2x4) to make enough room to apply spray foam to seal it up?

  • If you drill into the vinyl will probably kill the warranty. With the warmer weather(hopefully) remove the old caulking, clean and then reapply new caulking.
    – crip659
    Jun 3, 2022 at 20:22
  • I don't think the window being directly on top of a 2x4 is necessarily a bad thing. Adding some pictures so that we can see how the windows were installed will increase the chances of getting a good answer here. As it is, all we can do is guess. Don't make more holes trying to seal up existing holes. Without having the details, consider sealing from both sides of the window with a caulk formulated to better withstand cold temperatures.
    – gnicko
    Jun 3, 2022 at 20:59
  • You used the wrong caulk if it cracked. Silicone or urethane tolerate cold very well. I assume you calked between the window and the framing, and not somewhere conspicuous.
    – isherwood
    Jun 3, 2022 at 21:36
  • Have you considered that you want a shimmed gap at the bottom of the window frame to let this annoying stuff called "water" get out, instead of just sitting there where it can turn into mold, rot, etc? Jun 4, 2022 at 3:29
  • If water finds its way onto the sill, and there's no drain plane with a slope in it, you're going to have mold and rot anyway. A gap doesn't solve that. Modern construction in my area calls for sloped plastic trays installed under every window.
    – isherwood
    Jun 4, 2022 at 13:35

1 Answer 1


You've asked an XY question (about your solution rather than the problem). I'm not going to answer it. Instead, I'm going to tell you how I deal with this problem. Do not drill holes in your windows. (I guess I did answer it.)

  1. Remove the window casing (trim).
  2. Using a bit just larger than the foam dispenser tube, drill straight in between the window frame and the stud, sill, or header every 2-4" to about 3/4 the depth of the stud. Do your best to drill the wood, not the plastic. It helps to angle into the wood slightly when you start, then straighten out.
  3. Using your low-expansion spray foam, give each hole about a 1 second shot with the dispenser tube just shy of the bottom of the hole.
  4. After the foam sets, reinstall your trim.

The result will be the foam squeezing out into the small gap and filling nearly the entire void. Be aware that urethane foam bonds permanently to everything, including counter tops, floors, walls, curtains, and skin. Plan accordingly.

There are two ways to handle over-expansion: scrape and wipe as it emerges, or let it set and cut it off. You decide what makes more sense, but it will be messy if you do the former.

Here is my garage window, which I applied this technique to last winter. You can't really see the holes, but you can see the scars on the stud, and that it worked pretty darn well.

enter image description here

  • 1
    That's the right way to do it ;) Note PU foam does not bond to polyethylene. So you can put polyethylene membrane on the wall to protect it. Tape it right where you will drill and drill through the tape. The foam that oozes out will stick to the tape, but then you can rip the tape out when you're done. Whatever falls on the PE plastic is easily recovered later.
    – bobflux
    Jun 4, 2022 at 13:22

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