I'm a builder here in southern alberta Canada. we have just finished sheeting the roof of our latest icf constructed project. we have vaulted cieilings for the whole house, we want to use 2lb closed cell spray foam to seal everything up in the attic but don't want to break the bank doing it. what is the best way to achieve an r-40 attic with spray foam? the interior vaults are 5/12 pitch, i've been told that spraying a few inches of 2lb to the ceiling then blowing in celulose over it won't work because our vault is too steep and the celulose will settle out to the bottom of the vaults in a few years. any advise or experience with something like this. i hate to compromise the house by having an underinsulated attic. thanks,

If you are worried about settling, just combine the closed cell foam with fiberglass batts. You can put in about an inch of spray foam to get a R-6 or so, then put in a R-38 fiberglass batt to get up to R-44. The Foam/ FG batt method is often used on exterior walls, using 2*6 walls, a few inches of foam and a R-13 batt to fill the rest. You could even use wet spray in cellulose over the foam, but once you create the air seal with the foam, it doesn't really matter what you get the rest of your R value with, and there isn't really a reason to spend the extra money on the wet spray.

i know thats an option, i guess my only concern is the limited clearence in the vaulted attic. any ideas on how to do this before the ceiling is sheeted with drywall?

i used 5 inches of cc foam on my vaulted timber frame ceiling sprayed directly to the drywall on the ceiling

Have you considered using EPS sheet goods and then sealing with cc spray foam? Our sister company (EPS molders) manufactures EPS In Edmonton, AB. They can cut you what you need (even custom profiles) and you will achieve 4.5 R value per inch of EPS. 6" sheet goods of EPS will give you R36 and the cc spray foam should push you over the R40 you are looking for. This would be rigid insulation and should eliminate the settling issues you were concerned with. If you want pricing you can call EPS Molders at 780-477-7133 or toll free at 1-866-313-6994