Recommended Insulation R Values
LESLIE: We’re going to talk insulation with Mike in Florida. How can we help?
MIKE: Hi. Yeah, I had a question about r value insulation for a ceiling. I was wondering, in the state of Tennessee, what r value would you recommend for the ceiling.
TOM: Well, r value is resistance to heat loss and with fiberglass insulation there’s usually like three r per inch. So if you had 10-inch bats that would be r30. If you had a 12-inch bat that would be r36. I think that anything in the 10 to 12-inch area would be great for Tennessee.
The other thing I would caution you though, Mike, is to make sure that you also have ample ventilation in the roof space. Because if you add just a little bit of moisture to insulation it reduces the r value. In fact, two percent moisture will reduce your r value by a third. So if you have a damp attic, that 12 inches of insulation could have the same r value as, say, eight inches of insulation because it’s damp. It’s important that you have insulation and ventilation to have an energy efficient space.
MIKE: Thank you. That answers my question and some. Thanks a lot.
TOM: You’ve got it, Mike. Thanks so much for calling us at 888-MONEY-PIT.