Nigel writes from Berwyn, Pennsylvania: "I want to add attic insulation to at least R49, as recommended by the online DOE insulation calculator. My attic has 7" deep joists. I've purchased faced R19 for the first layer but, I'm finding that the 6.25" thickness is a maximum and the insulation surface is up to 2" below the top of the joist. The attic floor area is 1090 sq ft with gable vents of 6 sq ft total. There are no soffit vents.

Q1) For the insulation between the joists, is it better to use R19 (6.25" thickness) and have some dead air space between the joist layer and the traversing second layer or compress R30 (9.5" thickness) and have no dead air space?

Q2) Since there are no soffit vents, should the insulation still be prevented from touching the roof sheathing?

Q3) Would you recommend installing soffit or low roof vents to improve ventilation, especially since the insulation will be increased and the attic door weatherstripped to reduce convection?"

Answer: If you only have 7 inches to work with, I recommend two layers of R-15. If you have more space, I recommend two layers of R-30 - one with the facing down and a second layer unfaced going perpendicular to the first. As for ventilation, I recommend having a path for air to flow along the whole roof, including both entrances and exits. I recommend soffit vents. Owens Corning Raft-R-Mate® attic rafter vents will help you achieve an air channel for the soffit vents.