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Venting a cathedral ceiling with a reverse gable

2UV2SVyBqt | Posted in General Questions on

I’ve read several postings in your blog on the subject of roof venting and cathedraled ceilings but haven’t found an answer yet for my project. It’s a half story room above a garage that is completely unfinished on the second story. It has 5′ tall walls on the eave sides, built on top of a wooden I-joist floor system which is insulated with R-38 fiberglass. The roof is a 10/12 pitch, gable end on one side and attached to the existing house on the other. In the middle of the front (eave side) there is a 14′ wide reverse gable with a matching 10/12 pitch, but since its’ only the 14′ wide it’s ridge lands about 2/3’s of the way up to the main roof ridge. The entire roof was built with 2×12 rafters and it is completely unfinished on the inside. There is vented soffit material and ridge vent in place. My delema is this: the reverse gable was built with valley rafters and ridge beam that dead end into a 14′ wide header, 2/3’s of the way up the main roof, so if left this way all the rafter bays in that 14′ wide area wont breath properly once it’s closed in. I think spray foam would solve all problems but it’s not in the budget; does drilling holes and creating air channels truley work? I was thinking of drilling 1″ holes in the rafters, up close to the sheathing, of the effected bays, cutting rigid foam strips and laying them in left to right then the Proper vent on that. Any thoughts or better ideas. Thanks

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  1. GBA Editor
    Martin Holladay | | #1

    Roof venting is overrated -- IF you are capable of building a roof assembly that is close to airtight, and if you don't install any air-permeable insulation, and if your insulation has a high R-value.

    The roof you describe really can't be vented, so I'm afraid the answer is spray foam. If you don't want to use spray foam, you could install hundreds of individual pieces of rigid foam between the rafters, with each piece carefully air-sealed with canned foam. That's not a fun job, though.

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