Half of my windows got replaced just three years ago during the ownership of former residents. I realized that there is a large gap btw trim and windows. All new windows has this gap but old ones do not. I am not sure if this is a concern but i am worried about water penetration. Should I fill this large gaps with caulk, or install a new wider trim to close this gap? Thanks a lot.window replacement

  • That gap is between the storm window frame and the trim, not the window itself. It's very unlikely that's going to be an issue
    – FreeMan
    Commented Jun 27, 2022 at 14:09
  • Thanks- I do not know what storm window frame is. I will look it up online. In either case- you think no need to fill it with caulk?
    – victor
    Commented Jul 1, 2022 at 16:41

1 Answer 1


It is not to big of a gap. I have seen joints in commercial building as big as 1 1/2' It is all how the joint is prepared and the type of caulk used to fill the gap.

A 1/4" gap is completely acceptable for a caulk joint. If the surrounding surfaces are sound, no chipped paint, no rotted wood, you can fill it with caulk. In may cases because of movement between materials you need wo fill the gap with a "backer rod". This will keep the caulk from going too deep in the gap. The ideal thickness for caulk is 1/2 the depth to width ratio.

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This way the thinnest part can expand and contract easily as needed.

  • One more thing, the type of caulk I would use is a high end, long time guarantee latex caulk that claims it will last for at least 20 years. This way the excess caulk can be easily cleaned up with a well wrung out sponge. Too wet of a sponge will wash out the caulk. This way it will last between exterior paint jobs, where it can be refreshed/repaired if needed.
    – Jack
    Commented Jun 26, 2022 at 17:36
  • thanks, planning to use osi quad
    – victor
    Commented Jun 26, 2022 at 23:01
  • I have used OSI before and it is definitely not a water cleanup caulk. Although it is used by a lot of roofing and siding pros, it is something they use where the joints may not be so noticeable at least where roofing is concerned, and siding guys I hope will have a good "hand" at applying caulk neatly. If you never handled caulk to any great degree, OSI is not the product to learn on, Unless you use tape everywhere, clean al excess with the proper solvent then remove the tape. My preference is Polyseamseal, it is mildew resistant, guaranteed for a long time, and water cleanup.
    – Jack
    Commented Jun 27, 2022 at 2:12

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