Unvented roof assembly
Currently framing a home in Southern California (climate zone 3A), that contains “California Gables“. The hip roof is framed with a few small sections that contain a gable framed on top of the hip roof sheathing, leaving a small air space between the two layers of sheathing. In constructing a conditioned attic, I’m debating whether to use rigid foam above the sheathing or close cell foam under the sheathing? While I prefer to use rigid foam on top to reduce thermal bridging, I’m concerned about these few small areas of “secondary attic“, which are largely inaccessible and will not contain any insulation. Would this uninsulated, space, negate the effect of the rigid foam above it, and risk, condensation? Any suggestions/thoughts are appreciated.
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Replies
oren_h,
Can you describe these gables a bit more? Are they entirely decorative and built above the main roof sheathing? What is confusing me a bit is "leaving a small air space between the two layers of sheathing." Which two layers of sheathing?
Hi Malcolm,
Yes, the gable is purely decorative and is framed above the hip roof, but after the hip is sheathed. The gable of course has it's own sheathing on top. I attached a picture to illustrate. So my options are rigid foam above the gable sheathing or closed cell foam under the hip sheathing. There remains a small inaccessible space between the hip sheathing and gable sheathing. I hope that clarifies...
Any one have any thoughts here? Hoping for some input...
oren_h,
Sorry, I missed your response.
It messes up the sequence of construction a bit. but I'd consider installing the roof-top foam and sheathing, then framing the decorative dormers above those layers.