Attic: Hot roof? Cold roof? Closed? Open?
I live in Boston (Zone 5) in a 1924 colonial, and had some serious ice dam problems this winter. We've also had significantly below-normal temperatures, and my heating bill is astounding (despite new HVAC, wall insulation, new windows). The new HVAC includes a furnace/AC in the attic, with insulated flexible vents. So there are a lot of penetrations of the attic floor, including vents, potlights, electrical, etc.
I had an insulation contractor come by today looking to spray open-cell foam on my attic roof; I also requested a quote for closed cell.
Insulating an attic roof is against everything I have ever heard in my life, but I have been trying to read up on Building Science articles regarding hot roof systems. I am not really obsessing about shingle life; I am far more worried about water vapor, condensation, roof rot and the like. (We have a basement that is quite damp.)
So: Open cell, or closed? If open, with vapor barrier paint, or no? Does fire paint count as vapor barrier paint?
Does anybody know of any clear discussions or recommendations? I am a homeowner, and do not have time to become a professor of attic insulation. Clearly the building sciences are on a fence about this issue; they recommend both vented and unvented, with lots of caveats that are conveniently unavailable in real life.