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?
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.)
- Remove the window casing (trim).
- 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.
- 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.
- 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.