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Anyone know of a good article on how to spray foam the attic “floor” to create a vented, unconditioned attic?

tomsweets | Posted in Energy Efficiency and Durability on

I have been looking for a how-to guide on the ins and outs of spray foaming the floor of an unconditioned. Attic. I have found a great article from fine homebuilding 2009 by Michael Chandler, but it only covers how to create a conditioned (unvented) attic. I want my attic to have foam between/over the joists w/ baffles at the edges connecting to the soffit (a vented attic), but I haven’t been able to find a decent, detailed resource on how to do this. Anyone have any ideas?

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  1. user-1137156 | | #1

    What is the spacing of your ceiling joist or trusses? How much insulation are you planning? These questions lead to will your ceiling drywall sag due to insulation weight? In my situation, with trusses 24" OC and wanting r60+ of cellulose, the answer was/is without additional support the drywall will likely sag noticeably. The solution is OSB under the drywall. Having decided I need OSB I decided to raise my exterior walls 4" and create a " service cavity" above the drywall by hanging. (with metal brackets) 2x4s perpendicular to the trusses to support the drywall. Now spray foaming or otherwise sealing the ceiling plane is easily accomplished from the underside. I'll leave the ceiling "service cavity" empty. Since I'll have a similar but insulated service cavity in my double walls I will be able to do air leak testing before drywall.

  2. Expert Member
    ARMANDO COBO | | #2

    Have you checked Energy Complete by Owens Corning.? Great product to air seal attic floors and walls.

  3. GBA Editor
    Martin Holladay | | #3

    In most cases, this type of spray foam job is performed by a spray foam contractor, not a homeowner. I would discuss the details with your contractor.

    The first step of this job is to be sure that the ceiling has been prepared in a way to assure that the spray foam will limit air leaks. Certain types of equipment, including can lights and bathroom exhaust fans, will need to be protected. Your contractor should understand this.

    If you are interested in doing air sealing work yourself, I recommend GBA's 10-part video series, How to Air-Seal an Attic.

  4. wjrobinson | | #4

    Thomas, I agree with Martin. You need a spray company the has the experience to do the work. I know of one only near me, Northeast Sprayfoam.

  5. tomsweets | | #5

    Thanks for all the answers. I am working with a contractor who screwed up the original spray foam install. He has been a gentleman and is willing to fix his mistakes and discount the job, but I am trying to learn to check him because he has messed stuff up in the past.

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