On Aug 20, 3:16*pm, "HeyBub" wrote:
Wayne Whitney wrote:
On 2009-08-20, Aaron Fude wrote:

Just received a quote for roof insulation with closed cell foam
between the rafters. The quote is for 3" and I am being told that 3"
is 90% as good as 6". Do I believe them?

Are you insulating between the rafters because you'll be turning the
attic into habitable space?

As to your question, 6" of foam will be about twice as good an
insulator as 3" of foam. *If your concern is about reducing the
heating and cooling costs of the entire house, then the useful of the
extra 3" of foam depends on how well everything else is insulated.

Don't think so. Resulting efficiency rate drops off as thickness increases.
If you're at 50% with 3", you might be at 70% with 6" and 80% at 9" and 85%
at 12" (numbers are made up).

You're spot on about insulating the rest of the house. It won't do much good
to insulate the attic if you leave the front door open.

It depends on where you live, his 3" of foam could be R15-R21, mimimal
code for my zone 5 area is R 35 and optimal is R60. Heat rises and in
cold areas you do see a difference in even room comfort going to R 60.
If he is in a cold winter area 3" of foam for a roof-attic is a joke
in my area where it was -20f last year. Sure you get diminishing
returns but I was paying near 120 a month gas where a neighbor with
same size house that had crap windows and near no insulation paid near
700 one month for gas, up north here it is better to overdo efficency,
so you dont overpay utilities for the rest of your life. It also
increases resale value alot, or can make the sale in tough times.