Inusllating unvented cathedreal ceiling w/exposed rafters in S. California
My client has two bedrooms with vaulted ceilings, 4/12 pitch, exposed 4x4 rafters 3-1/4" thick, under 1" tongue and groove boards. The ceilings are unvented and the home is located in Southern California.
My plan was to fill the cavities with Hunter H Shield panels 2 1/2". Thereby leaving a 3/4" gap of dead air. Then running full sheets of 3/4" Rmax R-Matte Plus-3 unde the rafters. Then taping the seams of the Rmax with Tyvek housewrap tape, to try and air seal as much as possible.
Also, there are 4 fiberglass jboxes in roof that will be getting LED surface lighting installed. I was planning on using fireblocking foam to surruond the jboxes.
2.5" Hunter polyiso= R15.3
3/4" dead air = R2.77
3/4" Rmax = R5
Total Rvalue = 23.07
What do you guys think?