I've recently had wallpaper stripped and the guy managed to remove two of the PVC window trims in the process. This has exposed a gap between the top of the window and the wall of about 1.5 inches, and the same at the bottom beneath the sill a gap of approx 1 inch on half the length of the sill (see pics). The holes go right back about 5 inches deep. I haven't removed the other two sides of the trim but I can see behind them and the main gap is at the top and bottom of the windows.

I don't like the trim any way so happy to remove all of it, but my question is... how do I fill these gaps before I get the plasterer in? Do I need a tradesman to do this properly or can I do this myself - I am a complete novice with limited DIY experience albeit I am willing to give it a go if simple!

I've read that expanding foam might work, is the right? The room will be skimmed after I get this fixed, will I need to replace the trim afterwards or can I just caulk around the edge of the window to the new skimmed plaster? Any help greatly appreciated on how to fix this.

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  • Do you intend to install trim of a similar size? It's not clear whether you need plaster/drywall backing or just insulation.
    – isherwood
    Commented May 14, 2020 at 13:30
  • I am thinking I'd install a wooden trim of the same size, so I guess just insulation? I'm not sure if I'd put trim beneath the cill as it looks a bit odd there. Would welcome thoughts on that too! Commented May 14, 2020 at 13:32
  • "Sill". In that case, low-expansion spray foam will provide air sealing, insulation, and window stability with little effort.
    – isherwood
    Commented May 14, 2020 at 13:52
  • Welcome to DIYSE. Please take the tour to learn what to do next.
    – isherwood
    Commented May 14, 2020 at 13:55

2 Answers 2


Gaps around windows are common (there's a reason why they're called "rough-in"). As long as the gaps aren't larger than the trim, you're fine. Oddly enough, the old trim looks like it was attached to the window. That would explain the gap (it wasn't visible from the inside).

The unusual thing here is the size. Expanding foam is your friend here, but be sure it will fill a gap that large. Not all foam will expand 1" or more but there are types that can.


I’m failing to see what the problem is. If you want better insulation around window go ahead and use window and door spray foam. Other then that get yourself some new trim wide enough to hide the gaps. If you choose to use some spray foam, Only use window and door spray foam, nothing else.

  • The "problem", as you say, is that the Beth does not have the knowledge of how windows are installed in a rough openings or how they are supposed to be insulated. You are "failing to see the problem" because you are assuming the OP has the same knowledge that you do. You do not explain in your "answer" how to accomplish the advise you are giving.
    – Alaska Man
    Commented May 14, 2020 at 16:46

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