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Patio roof on top of insulated roof detail?

dsmcn | Posted in GBA Pro Help on

Zone 4A, hip roof with 4:12 pitch; spray foam insulation to be on the interior side of the roof deck (not ventilated). I will be adjoining a new roof out over a patio, placing the new ridge and rafters on top of the existing zip sheathing . The patio roof will have exposed rafters, and the wall of the house will extend up to the new ridge, so the part behind this vertical wall that joins with the existing roof will create a dead space.

Question: is the dead space between insulated roof deck and addition an issue?

If it is an issue, would a ridge vent over this section be a remedy? Or a vent in the wall below the porch rafters? Or both?

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  1. GBA Editor
    Martin Holladay | | #1

    The dead air space you describe should be fine. There is no source of moisture (as long as you don't have a roof leak). Because of solar radiation, this type of attic is almost always very dry.

    If you want to install a ridge vent, you can. (In a colder, snowier climate zone, I would advise against a ridge vent, since ridge vents sometimes admit wind-blown snow. But if your climate zone doesn't get blizzards -- and I'm guessing it doesn't -- then a ridge vent will do no harm.)

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