Vaulted ceiling insulation advice?
I’m looking to do a re-roof on my home and want to improve the insulation at the same time. After reading this article, I am leaning towards option 1 identified there:
Here are the details:
-Home located in climate zone 3, southern California.
-Saltbox style roof, but the front is 1 story, rear is 2 story
-Mostly vaulted ceilings with no attic, two small sections have attic space (details below)
-Soffit vents to ridge vent. There is a 4’x8′ skylight in one section of a vaulted ceiling
-2×6 rafters spaced @ 24″
-Very poor insulation (3″ batting labeled as R11 from Rockwool. Most appears detached from sheathing)
-1×6 solid board sheathing with small (1/4″) gaps – appears to be in good condition
-Front roof pitch is 7:12
-Back roof pitch is 4:12 or 5:12
Current roof layering (inside-out):
-Ancient 3″ Rockwool R-11 batting in a 2×6″ rafter cavity, mostly detached
-1×6″ solid board sheathing
-2 layers of fiberglass composite shingles
One 1st floor bedroom has an attic underneath. This attic space does has one soffit vent but doesn’t appear to connect to the ridge vent, nor does it have a gable vent.
Another small section of roofing over a 2nd floor shower has a tiny attic. This attic space is not accessible, but has a gable vent. There is also a whirly bird on the rear section of roof that appears to be directly in a rafter cavity.
What I plan to do:
-Remove all shingles and underlayment
-Remove whirly bird and seal gable vent over small attic space
-Repair any damaged 1×6″ sheathing, but largely keep as-is
-Leave existing rafter insulation alone
-New airtight membrane
-7″ polyiso rigid foam with staggered and taped seams (two layers of 3.5″)
-OSB or plywood sheathing (no ventilation gap)
-Underlayment & new composite shingles
I would treat the roofing over the small attic areas the same as the rest of the house. Basically following what is in this video:
-Does the above plan seem reasonable given the information?
-What type of air membrane is recommended?
-In my climate zone, is there any benefit to installing vents over the foam?
-How does the foam connect at the ridge? I assume there is no ridge vent in
-Do I need to close off the existing soffit vents in the rafters? If so, what is the recommended way to do this? Most of the house is stucco, and I would rather not have to cut into it.
-Are 8+” screws sufficient to hold this much foam and roof sheathing in place, particularly on a such a high pitch roof?
-Any special considerations that need to be made around the skylight?
-How does the above plan compare to installing a “Cool Roof”? When I first started looking at this, I had a few roofing contractors estimate a reroof and none of them had used rigid foam. They pushed installing a Cool Roof which reflects most of the infrared light but doesn’t do anything related to insulation.