Hello! I have a 24′ x 28′ house in northern minnesota. The house was built in 1970 – but not for winter use. There is insufficient venting and insulation and the shingles are original. In planning the venting, insulation and roofing improvements, I came across this 1996 article

http://homeenergy.org/archive/hem.dis.anl.gov/eehem/96/961110.html

on installing insulation at the edge of a shallow-pitched roof. I was planning on blowing in cellulose on top of the existing (3″?) fiberglass batts. The rafters and ceiling joists are 5(1/4)”.  The article above suggests:

“Polyisocyanurate foam board, such as Thermax, is rated R-7 per inch. Cut the insulation into strips and stack layers of these strips between the rafters and the ceiling joists directly over the outside wall. Cut the strips so they fit snugly against the framing members of the roof and ceiling. Be sure they extend 2 ft into the attic, and leave 1 1/2 inches above the stack to allow air to pass for soffit-to-ridge venting. Seal the strips to the framing members with canned spray foam to make the connection airtight. “

Since I would be re-roofing, the existing shingles and sheathing would be removed from the lower edge of the roof.

This approach makes a lot of sense to me. What do you think?

I also had a couple of questions on some details: Should I remove the fiberglass batts where I put the rigid foam? If I remove the fiberglass, do I leave the kraft paper down and rip up the fiberglass? Is polyisocyanurate foam board with foil better? If so, which way should the foil face?

Thanks for your thoughts!