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Seal foam attic baffles at kneewall

CTSNicholas | Posted in Green Products and Materials on

I am installing the foam version of the attic ventilation baffle at my kneewalls so that I can blow in a good amount of cellulose. The online video from the manufacturer shows them simply hammer-stapling these along the trusses. Two things I notice, 1.) These things rattle like nothing else when air is coming from my vented soffit at the right speed/angle because there is nothing pinning these tight to the underside of my roof’s OSB (ideally I’ll have enough insulation to keep them somewhat tight) but I don’t think it’ll be *that* deep. 2.) These have visible holes where they fold down from top plate of wall to the angle of my roof. I’m just using spray foam to fill the voids and cracks or damaged pieces…any other suggestions? The foam appears to stick well once hardened.

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  1. GBA Editor
    Martin Holladay | | #1

    It's hard to visualize what product you're talking about -- you describe it as "the foam version of the attic ventilation baffle." If you're talking about the thin polystyrene baffles, I think you've chosen the wrong product for a cellulose application. You need something sturdier (to resist the pressure of the cellulose).

    I'm not sure whether you are talking about a cathedral ceiling with dense-packed cellulose or a vented unconditioned attic with insulation on the attic floor.

    To learn more about these issues, see these two articles:

    Site-Built Ventilation Baffles for Roofs

    How to Install Cellulose Insulation

  2. CTSNicholas | | #2

    Martin, you're saying you can't just read my mind?! What a bummer!!

    Sorry, to clarify... This is a vented attic. I have vented soffit and ridge vent all along the main ridge. Roof style is hip. Climate zone 5. I'm using the Duravent brand thin foam baffles because they are the only ones sold here that fold down to cover the gap between trusses above the top plate.

    I will be blowing in cellulose. Not dense packed to my knowledge. I don't think it will destroy the foam baffles as long as I'm careful.

  3. GBA Editor
    Martin Holladay | | #3

    You can get away with using the thin polystyrene baffles from Duravent, as long as you are careful. They're not my favorite, however. They are (a) fragile, (b) not deep enough (since the ventilation channel they provide isn't a full 2 inches deep), and (c) not wide enough (since they don't provide a ventilation gap that is as wide as the entire rafter bay).

    As I said, there are better alternatives mentioned in this article: Site-Built Ventilation Baffles for Roofs.

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