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Unvented Rafter Bays over Unconditioned Space

ktoblesky | Posted in Building Code Questions on

I have a question regarding an unvented rafter bay for a roof the is over an exterior deck, not conditioned space. Do I need to apply IRC R806.5 or is that just for roofs over conditioned space? I don’t want to create any condensation issues as the project is in the hills above Reno. Hot in the summer cold and snow in the winter.



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  1. GBA Editor
    Kiley Jacques | | #1

    I’m giving your question a bump. While you wait for experts to weigh in, consider these words: “Unvented roofs in the snow belt may still need some type of venting to keep the roof cold and prevent ice dams.”

  2. ktoblesky | | #2

    Thanks Kiley. I appreciate it.

  3. rszimm | | #3

    Are the rafter bays enclosed? (Ie, do you have a ceiling over the deck, or exposed rafters). If exposed, I’d say certainly not. If enclosed I’d also likely say you don’t need it, but it gets a bit more iffy. You want to keep the whole assembly the same temperature. Exposed bays makes this easy. An enclosed bay has the potential to have a temperature gradient that would cause condensation. Honestly though this seems a bit theoretical. I do not believe IRC requires it.

    1. ktoblesky | | #4

      Thanks for the response. Yes the rafters do have a ceiling so the bays are enclosed.

  4. Jon_R | | #5

    IRC R806.5 should be for "above conditioned space". But I don't see where it says that. It gets even trickier if the space is occasionally conditioned.

    I've seen some moisture problems in/above unconditioned spaces, but never in a dry place like Reno.

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