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Community and Q&A

Can’t fit polyiso boards through trusses, even with folding

ps24eva | Posted in Energy Efficiency and Durability on

I did one side of a bonus room okay with folding the polyiso boards various ways.

The other side I probably can’t do because of the smaller hole available to me.

Is there any alternative besides housewrap?

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  1. Expert Member
    Dana Dorsett | | #1

    Draw us a picture- I'm confused!

  2. ps24eva | | #2

    I am insulating a kneewall on the attic side.

    I can't use polyiso.

    Are there any other alternatives besides housewrap?

  3. user-2310254 | | #3


    Both kneewalls are inside your attic, correct? Where are you located? Did you install housewrap and rigid foam on the exterior of your home over the sheathing?

  4. GBA Editor
    Martin Holladay | | #4

    It sounds like your kneewalls are insulated with a fluffy insulation like fiberglass batts, and you are trying to install an air barrier on the attic side.

    Yes, you can use housewrap as the air barrier. Rigid foam would be better (because it reduces thermal bridging through the studs), but housewrap will work. Remember to install the housewrap with attention to airtightness. Tape the seams with housewrap tape.

  5. ps24eva | | #5

    Instead of polyiso/housewrap, is there a decent closed cell spray foam kit for a small area?

  6. Expert Member
    Dana Dorsett | | #6

    A picture is worth 1000 words. So far the description has been fewer than 100, leaving us all guessing.

  7. GBA Editor
    Martin Holladay | | #7

    Several manufacturers sell two-component spray foam kits -- you can usually buy such a kit at your local lumberyard.

    But you need a substrate. I don't recommend that you spray the foam onto fiberglass batts.

    Moreover, if the space is very tight, and you are lying on your back at an awkward angle, that's not a position that is conducive to using a two-component spray foam kit.

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