I have a home with Hardie Board siding and trim. There is a tiny gap between the edge of the installed windows and the Hardie trim board ( Please see the gap where my finger is pointing in the picture below). It’s kind of hard to see in picture because the gap itself is black and blends in with the window, however, the gap is a around 1/8th to 1/16th of an inch wide and goes all the way around the window. The gap is due to the white trim not completely touching the window housing itself.

Should this gap be caulked or am I missing something? I plan on using silicone to seal that gap on the top, left, and right sides. I’d leave the bottom unsealed so it doesn’t trap moisture.

Gap Between Window Housing and Trim Wider View of the Window

1 Answer 1


Yes for sure. The caulk is rather important there more than anywhere else because water will run down those channels and rot out the window framing and window itself (rust if metal).

I suggest ge5020 concrete and masonry silicone ii and to do this window in clear or black. I would not match trim color as something that light will show dirt more and you will end up with brown or grey very soon.

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