GBA Logo horizontal Facebook LinkedIn Email Pinterest Twitter Instagram YouTube Icon Navigation Search Icon Main Search Icon Video Play Icon Plus Icon Minus Icon Picture icon Hamburger Icon Close Icon Sorted

Community and Q&A

Sealing Gap on Vinyl Casement Window

Trevor Lambert | Posted in General Questions on

One of the windows in my house has a manufacturing defect that makes the frame not square. This is an operable, casement window, and since the operable part is square, the result is a gap at one corner that won’t seal; it’s about 2-3mm wide at the corner, narrowing to nothing maybe 30cm away from the corner.

After years of trying to get some sort of solution from the manufacturer, I’ve given up. The first couple of winters I just taped that window closed; last winter I used temporary “draft seal” sealant.

My idea for a long term fix (ok,hack) is to adhere a strip of plastic to the top of the operable window which will bridge the gap and make contact with the sealing gasket on the frame. I’ll stick it on there with wet-grab no-more-nails for air sealing and some structure, and also screw it down for main structural attachment.

If someone has a better idea, I’m happy to hear it, but mainly I’m just wondering which plastic I should use. Vinyl would make sense, but finding square stock of it has proven difficult. The readily available options are HPDE and clear acrylic (polycarnonate, I think). Is either of these better in terms of adhesion. The HPDE will blend in better visually, but I have my doubts about any adhesive sticking to it. It also might be too flexible.


GBA Prime

Join the leading community of building science experts

Become a GBA Prime member and get instant access to the latest developments in green building, research, and reports from the field.


  1. Expert Member
    Akos | | #1

    Try the trim isle of your local box store. There are a lot of shapes available in vinyl for exterior trim work.

    1. Trevor Lambert | | #2

      I've been to all the box stores around me. They don't sell trim, as far as I can tell. Or at least they don't stock it in the store. Both siding and trim seem to be special order only items.

      So right after posting, I went to look online and I do see some interior PVC trim. It's not an ideal profile, but I'll consider machining it up. Probably ruin a saw blade to do it. Oh, wait, it's cellular PVC. Hmm.

  2. Jason S. | | #3

    Better idea: pull the whole window out and install a fiberglass frame one. Worth it ;)

    Alternatively, could you just adhere or fasten a bigger weatherstrip to the frame? I imagine you could find an epdm gasket profile that works, as long as there's at least some frame/sash overlap.

Log in or create an account to post an answer.


Recent Questions and Replies

  • |
  • |
  • |
  • |