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Community and Q&A

Cathedral ceiling rigid foam vents?

TravelingSwede | Posted in Energy Efficiency and Durability on

New construction — having the attic trusses built with 18″ top chord for insulation and baffles. Not totally sold on spray foam.

The question is: doesn’t building vents with foam or using plastic vents that are sealed to the truss create an area of condensation (it shouldn’t condensate with that much insulation)? Or at least, in the event it did get wet, doesn’t give it the ability to dry to the outside?

The drywall inside will be sealed and there is only one roof penetration design for plumbing vent.

Should I build vents that let the insulation breathe to the vent system?

Jeff Anderson

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  1. GBA Editor
    Martin Holladay | | #1

    If you build your cathedral ceiling assembly properly -- that is, with a ceiling air barrier and careful insulation installation -- you shouldn't get condensation on your vent baffles.

    However, if you want to install vapor-permeable baffles, you are free to do so. Many builders use fiberboard sheathing or stiff cardboard for this purpose -- both materials are vapor-permeable.

    Just make sure that your baffles are installed in an airtight manner.

    More information here: How to Build an Insulated Cathedral Ceiling.

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