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Community and Q&A

Insulated ceiling detail

dixmont | Posted in General Questions on

Thanks for the forum. I’m trying to figure out the best method to insulate the flat ceiling of a single story house. The house is in Maine, Zone 6. Roof trusses with non-occupied, vented attic space. My original plan was to strap the trusses at 16″ O.C. and install drywall. I prefer not to use poly/plastic and instead opt for the latex barrier and do a good job with the air ceiling at penetrations. For insulation I was thinking un-faced fiberglass between the truss chords, butted tight and topped with blown in cellulose. I’m not interested in spray foam for the ceiling.

I have read several posts on using all blown in to minimize voids. I like the idea, but not sure how to accomplish this without putting up poly before strapping or something else to hold it up. I’ve read of people using Tyvek or netting under strapping to hold up the blown in. Then the whole issue with the air void between the drywall and insulation and a convection loop (not sure how this works). Basically, I’m wondering what others are seeing/using in the Northeast and any recommendations? Thanks.

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  1. Expert Member
    Dana Dorsett | | #1

    Most people would just blow the insulation onto the drywall and let the drywall support it. If you opt put up polyethylene sheeting it can go on the underside of the strapping after shimming it all flat, before installing the drywall.

  2. GBA Editor
    Martin Holladay | | #2

    First you install the drywall ceiling. Then you install the blown-in insulation.

    For more information, see How to Insulate an Attic Floor.

  3. dixmont | | #3

    Thank you. I like the idea of the Class II vapor retarder for the climate here. Any thoughts on using the Certainteed Membrain product on the ceiling (between strapping and truss chords) vs. Benjamin Moore Vapor Barrier 260 applied to the drywall?

  4. Expert Member
    Dana Dorsett | | #4

    Either will work.

    MemBrain can be detailed as as an air-barrier for redundancy (the wallboard should be detailed as well), whereas VB 260 cannot.

    Use ring-shank nails or screws for the furring. to better manage the weight over time.

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