I have a steel frame workshop with metal siding that I want to add a window unit A/C to. In order to do that I will have to cut a window sized hole in the side of the building and with that I will need a way to trim out/seal said hole.

I have found several guides online for metal siding trim before it's up but have found nothing for doing it in place. Will I have to pull the siding down or is there a method for doing this in place?

  • I would imagine it's pretty much the same, except that you'll have to slip the trim pieces under the existing siding and screw through instead of putting them in place first then siding over. I'd invest in a couple extra tubes of silicone caulk for all the screw holes. But I'm no expert on steel siding, so a comment, not an answer.
    – FreeMan
    Jul 20, 2022 at 11:26
  • Will go with @FreeMan thinking. Trim is usually put on first to hide the screw/nails with the siding. You will probably need to make supports for the AC unit, since the siding probably will not strong/rigid enough
    – crip659
    Jul 20, 2022 at 12:04
  • 1
    Good point, @crip659. Or, maybe, add a horizontal support beam across the bottom of the opening between the studs. That may require opening up more of the wall, but would be the most secure way of doing it.
    – FreeMan
    Jul 20, 2022 at 12:27


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