Regarding site-built ventilation barriers
brooks4848
| Posted in GBA Pro Help on
If one were to install with 2″ rigid foam within the rafter bay then fill the remaining space of the rafter toward the interior of the living space with unfaced fiberglass insulation, would this work?
Then would it be possible to cover this with sheetrock or wood paneling? Thanks.
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Replies
Brooks,
It sounds like you want to build a ventilated roof assembly. If I understand you correctly, your suggested approach will work, but only if:
1. You maintain an air gap for ventilation between the top of the insulation layer and the underside of the roof sheathing.
2. You air gap is continuous, from the soffit to the ridge vent.
3. Your total R-value meets minimum code requirements (R-49 in the northern half of the U.S.). This can be a problem with conventional rafters, which usually aren't deep enough to provide room for the required insulation.
4. You have an air barrier on the underside (the interior side) of your fiberglass batts. (Wood paneling won't do unless there is an air barrier above the wood paneling.)
For more information on these questions, see How to Build an Insulated Cathedral Ceiling.