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Can I use spray foam insulation on attic trusses on an ICF home?

Jim McKay | Posted in Green Building Techniques on

I am building an ICF home using Reward walls, footings to rafter, with no sill plate, but using hurricane straps. Walls are 13″ with 2.5′ on each side for insulation and 8″ of concrete fills the cavity.

I have attic trusses and am unsure how to best insulate this without having moisture problems with this tight of a home. It looks like I can use a minimum of 2 inches of spray foam and then fill the rafter top cords with batt insulation. Does the entire rafter cavity need to be filled? The trusses are varing lengths with the open living space just under 14 total feet.

Do I insulate the side walls if I insulate the entire rafter? I also have one area that overhangs 5 feet. Does this pose any additional concerns if I do not vent this area? Looking for advice.

Thanks,

Jim

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Replies

  1. GBA Editor
    Martin Holladay | | #1

    Jim,
    First of all, it is unclear from your question whether you intend to insulate the attic floor or the sloped roof. It's always better to insulate the attic floor, unless you have ductwork or HVAC equipment in your attic, or unless you have plans to convert the attic to living space.

    If you decide that you prefer to insulate the sloped roof, then of course it's also necessary to insulate the gable walls in the attic.

    You can use spray foam to insulate a sloped roof if you want, but it isn't the only way to proceed. Attic floors are best insulated with cellulose insulation.

    For more information on these issues, see:

    Creating a Conditioned Attic

    Vented or Unvented Attic?

  2. Mike Collignon | | #2

    Jim:

    Sounds like it will be a great home, but my question to you is: why are you using 8" forms for the above-grade walls? You could easily use 6" or even 4" forms, still have an incredibly strong structure that is energy efficient, and save you some money on materials.

    Just a thought.

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