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Community and Q&A

Unvented Roof

mhunt11 | Posted in General Questions on

We plan on creating an unvented 1:12 pitch roof  assembly with standing seam metal panels and closed cell spray foam on the interior.  Does the roof decking/OSB need to have gaps in between each board for expansion/contraction on an unvented roof assembly? Also will Owens Corning Titanium PSU30 be an adequate underlayment for an unvented roof? (it is rated for 1:12 pitches under metal panels but not sure if it’s ok for unvented assembly).

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  1. Expert Member


    All sheathing should be gapped 1/8". Most commodity sheet goods are sized taking that into account.

  2. Expert Member
    Akos | | #2

    I never dug that deep into the data sheet for the underlayments. I've used Grace HT product and FT Planinum HT with unvented roofs without issues.

    I can't really see what the venting of the roof has to do with the underlayment as all of these are vapor barriers, which is fine with closed cell SPF under the roof deck.

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