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Community and Q&A

Window Gaskets

John Nooncaster | Posted in Energy Efficiency and Durability on

Could anyone share their opinions regarding the use of gaskets versus LE foam for air sealing around windows and doors?


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  1. John Klingel | | #1

    I've read, and believe, that EPDM gaskets will not dry and get brittle. If whatever they are against moves (tweaking, shrinking, etc) they can expand and continue sealing. Foam is brittle. I'm going w/ gaskets whenever possible... and hoping. j

  2. GBA Editor
    Martin Holladay | | #2

    In Europe, builders concerned about airtightness favor gaskets over spray foam. Research shows that properly sized gaskets perform better than spray foam when it comes to sealing seams between SIPs, gaps under bottom plates, and gaps around windows.

  3. John Reimers | | #3

    How do you use gaskets to seal around windows? Do you bend them at a 90 degree angle and attach to framing and window frame? Cram them into the space between the window and wood framing that you would normally fill with foam? I can't quite picture this. Thanks for the clarification.

  4. GBA Editor
    Martin Holladay | | #4

    More information on gaskets can be found here: Air-Sealing Tapes and Gaskets.

    In that article, I wrote, "For sealing cracks around windows, Conservation Technology recommends the use of 'gap gaskets.' The two most useful sizes are #BG44, a 13-millimeter gasket that seals gaps from 1⁄4 inch to 1⁄2 inch, and #BG46, a 21-millimeter gasket that seals gaps from 3/8 inch to 3⁄4 inch."

    It's best to plan your rough openings so that the gap between the window frame and the rough opening corresponds to the size of the gasket you intend to use.

    To insert a gasket into a gap, I like to use a cedar shingle. You can choose a shingle with the right width to suit your preference -- narrow or wide, as you prefer -- and you can cut the shingle with a utility knife to get any thickness you want, from a tiny crack to almost 1/4 inch. A cedar shingle is less likely to damage the gasket than a screwdriver.

  5. John Brooks | | #5

    Although many people seem to think gaskets are a good idea....

    It is hard to get much feedback from people(in US) who are currently using gaskets with windows, drywall and or sheathing.

    Gaskets.... EPDM ...sure sound like a good idea to me

    I would sure like to read more reports and accounts...good or bad

  6. Bob Coleman | | #7

    if you are using shims, how are gaskets compatible/installed?

  7. GBA Editor
    Martin Holladay | | #8

    The gaskets are not continuous; obviously the gasket is interrupted by any shims. This would be a good location for a high-quality caulk to minimize air leakage.

  8. Danny Kelly | | #9

    Seems to me you may need to use both. If you use a gasket to stop the air leaks - you need to insulate the rest of the cavity to achieve proper R-Value so need to fill this gap with foam unless you want to chink fiberglass after the gasket is installed but not sure how well that will work. I see this alot - builders air sealing with a bead of foam but leaving the remainder of the stud depth pretty much uninsulated - ideally this gap meets the same R-value as the rest of your wall.

  9. Albert Rooks | | #10

    To make a high quality air seal on the interior side of windows: Gaskets, foam and caulking are certainly the tools at hand, may pass initial tests, but will fail as the building moves and framing dries out. As they rely on the opening remaining the same and not dimensionally changing, they are not a longterm air seal. The opening (of wood frame construction) will change as the lumber dries out and seasonally changes, the building settles, etc.. When this happens, there is not enough elasticity in foam or caulking to maintain an air seal. The gaskets will have varying success depending on how much compression is maintained around the opening. inThe high R value european windows from Optiwin or Enersign come with some form of adhesive tape for air sealing. Foams, caulking and gaskets are a temporary measure at best, not one that will maintain air sealing for the life of the window. Obviously, if you have one of these high end windows, the tape is included. When it's not, try SIGA Corvum 12/48. It is made for windows. It's has a 12mm leg and a 48mm leg (1/2" & 2"). The 12mm leg goes around the window. As it's 1/2", it's easy to maintain a line that gets covered by trim. The tape is pre-folded with one side ready to stick. Corners are done by making a pre-folded corner (see pic). You place the pre-folded corners in each window corner and then tape the field between the corners. The window opening can move and the tape can move with it as it has a 90 degree bend and 48mm's wide of sealing against the framing.

    I'll attach pictures below. It's simple, cuts down on time and will last as long as the window does. A better description is at, or

    Al Cobb at the SIPs School just tried it out on a job. I have no idea how it went for him. Perhaps he has an independent opinion of how it worked...

  10. Albert Rooks | | #11

    Sorry. I had trouble getting the pics up. Here they are. (??)

  11. Bob Coleman | | #12

    interesting albert, thx for the reply

    curious as to why this solution is not used stateside... there are plenty of tape makers that could push this, even if their tape is not as reliable

    also impressed that the sig tape will hold with such a small piece against the actual window; i'd say you'd need the bigger 30/30 for shim type installation because of the larger gap

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