Hi, my wife and I live in western New York in a house we bought last year. Our house is well insulated and weather-tight except for one area. This area was once attic space that the previous owner converted to a loft overlooking the kitchen. Its ceiling is framed with 2x6s and the finished ceiling (drywall) is sloped/vaulted. There is currently R-19 fiberglass jammed into the 5.5 rafter cavity with a cheap Styrofoam type baffle that is most likely crushed in several spots. This area is the only one that continually melts snow in the winter resulting in ice dams. Heat during the summer also builds up in the loft due to the roof heat coming into the house.
I would like to take the dry wall down and replace the fiberglass with rigid board. This is the only way I can get close to R-38 without lowering the ceiling too much (peak of the ceiling is approx 4 above the loft floor). I have looked into spray expanding foam, but even that doesnt give me the R-value without adding more rigid board. The only thing I am concerned with is how much the rafters expand due to summer humidity. If I re-insulate during the summer tightly squeezing the insulation boards between the rafters, will the foam boards become loose during the winter when the rafters dry out and possibly shrink? Also, do I need to get the insulation value up to R-38, or is R-30 enough to keep the snow on the roof?
Thanks for any help given me.