Install Insulation Properly in an Attic
LESLIE: Thomas is looking to gain some energy efficiency by insulating the attic. How can we help you with this project?
THOMAS: I want to put insulation on the roof in the attic …
THOMAS: … and I was wondering can you just put the insulation right up or do you get condensation between the roof and the insulation.
TOM: Yeah, you don’t want to put the insulation right on the underside of the roof itself. You want to put it at the ceiling level; in other words, the second floor ceiling between the …
LESLIE: Conditioned spaces and unconditioned spaces, correct?
TOM: Yeah, exactly. If you’re talking about putting it up on the roof rafters, that would be a bad idea.
THOMAS: I thought so.
TOM: Yep, bad idea. Because it holds too much heat against the roof it will wear out the shingles very, very quickly; it will trap moisture in there and cause condensation and delamination and mold. The only time that you insulate in that particular space is if you have a cathedral ceiling where, say, you have like a 2×10 roof rafter; then you put in about eight inches of insulation and leave a gap between the insulation and the underside of the roof sheathing, Tom, but in this particular situation I would put it down on the attic floor or the second floor ceiling level. You’re going to want about 15 to 18 inches of insulation there.
THOMAS: Oh, OK. Alright.
TOM: Alright, Tom. Good luck with that project. Thanks so much for calling us at 888-MONEY-PIT.