While remodeling an older wooden house, we decided to put vinyl siding. The workers put up the siding but when it come to the windows, they didn’t use any trimming, no j channels, nothing. The siding is just bugged up against the window. I asked, wouldn’t this leak and was told no it wouldn’t. However, I noticed I can feel air coming from the window if I put my hand by it. What should I do?

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    I can't begin to see any detail from that tiny photo. If you want help we need to see the situation clearly.
    – isherwood
    Commented Jul 26, 2021 at 15:36
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    Also, your question about air leaks has nothing to do with siding. Siding, especially vinyl, is not an air barrier. That's under the siding in the form of a house wrap membrane or similar. Air leaks are a caulking or sealing tape issue. You'd have to show us what's under the siding for help with that.
    – isherwood
    Commented Jul 26, 2021 at 15:37
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    Did you mean "butted against the window"? I'm not sure what "bugged" is.
    – isherwood
    Commented Jul 26, 2021 at 15:38

1 Answer 1


For the sides of the window, at least, "J channel" trim is just for looks; it's so the crew doing the siding, who are likely working very quickly, don't have to be particularly precise in their cuts... the J Channel acts as a trim (which, by definition in construction/building, is just finishing/aesthetic additions, not necessarily functional, though some trim can be functional, too) that the ends of your vinyl siding slide into, hidden from sight.

The one place it might be needed is above a window or door, where it can act as a way to catch and divert water from getting behind the siding somehow... but it depends on how they frame, caulk, and side around the top side of the openings. We would need to see a close-up of the sides to know more.

As far as leaks go, you seal a window against air and water before it is sided. That process occurs before siding is ever put up. If your window opening is not sealed before the vinyl is up, it's too late to seal it and you will need to take the vinyl siding off and take the window out and seal the opening.

The air you feel is unrelated to the use (or lack thereof) of any J Channel. Vinyl siding is not airtight, so adding J Channel would do nothing to stop that air you feel.

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