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Air sealing and insulating trusses roof

SammuelM | Posted in General Questions on

I am ready to insulate my home which is a new construction. I originally planned to spray the roof deck with open cell and the walls with closed cell but decided to switch to sheep’s wool. My main concern comes with insulating the roof deck. I have engineered trusses with a bonus room.

My plan is to vent the roof deck with baffles and fur out the trusses to achieve at minimum an R-38.

My thought is to use 2” rigid foam to construct baffles from the top plate to the ridge, which would also act as an air seal (if that would provide an air seal which is my main question), outside of that would go wool insulation.

would the rigid board between trusses provide an air seal or would I need to rely on something like drywall?

Should I be concerned with the uncovered wood members of the trusses?

My aim is to keep the air seal and insulation against the walls and the roof deck.

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Replies

  1. bpontolilo | | #1

    Hey Sammuel,

    I have seen a lot of projects from designers and builders I trust where site made ventilation channels are installed as you describe. One thing you left out of your description is how you will seal the rigid foam to make it airtight. You'll need to seal it to the framing and seal any seams in the rigid foam. Canned spray foam, sealants, and tapes are all options, though I've heard lots of reports of canned spray foam being unreliable over the long term, and as wood moves. Air leaks are a common culprit for roof issues, so I'd still consider an air barrier at the drywall, either the drywall itself or a membrane. For others to give you helpful replies, they'll want to know what climate zone you are in (where the project is located). In the meantime, here are some helpful articles:

    How to Build an Insulated Cathedral Ceiling
    Site-Built Ventilation Baffles for Roofs

  2. SammuelM | | #2

    Thank you. I’m building in Riceville, TN which is in zone 4.

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