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Community and Q&A

Cellulose Drying Potential / Vapor Retarder

Jason Mann | Posted in Green Building Techniques on

I’m building a single-story 36×40 foot office next door to my house.

Here are the details:

Double-stud walls (2×4’s, total depth of 9.25″ before sheathing.) Sheathing will be Zip panel, with taped seams.
The building sits on posts. We installed PT plywood to the underside of our 2×10 floor joists. The subfloor is Advantek. We plan to dense pack this floor and the walls with cellulose.
The roof will be 10″ deep I-joists, sheathed with Zip. We also plan to dense pack the roof.

So here’s my question: Is it safe to assume that the cellulose will dry to the interior of the building? Or should I install a smart membrane (Intello?) to the inside of the walls and ceilings before blowing in the cellulose?

I’m planning to tape all the seams in the Zip panel. I was also going to spray foam or caulk the seam where the I-joists land on the top and bottom plate, and anywhere else it seems like we could have significant air infiltration.

So… go the Intello route? Skip it?

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Replies

  1. Jon R | | #1

    Make sure that the wall complies with the recommendations in Table 2 A or B here.

    The same info could be used for the floor. For the roof, see the IRC building code.

    Smart retarders add additional resilience over fixed perm retarders.

    > seems like we could have significant air infiltration

    Far better to test.

  2. GBA Editor
    Kiley Jacques | | #2

    Hi Jason,

    You didn’t mention your climate zone, which is key to your decision. This article from Martin Holladay might be useful to you. He talks specifically about Intello Plus but also explains why “you don’t have to buy a smart vapor retarder . . . [because] many common building materials—including the kraft facing on fiberglass batts, asphalt felt, vapor-retarder paint, plywood, and OSB—restrict vapor flow when dry, but become more vapor-open when damp.”

  3. Jason Mann | | #3

    Ah, you're right. I am in midcoast Maine, which is Zone 6.

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