You use fiberglass insulation under the rigid board to create a higher r-value insulation while moving the thermal envelope.
Appreciate your reply!
To be sure I understand, one would put (at least) R-19 fiberglass bats, between roof rafters, then put rigid board along bottom edge of rafters. Correct?
I currently have blown-in insulation between [8"] ceiling joists. If I attend the rafters, as per above, will that then suffice [assuming all other air gaps between living space & attic are stopped] as far as insulating the attic?
Attending the rafters w/insulation is going to be quite expensive!