apostolakisl
Senior Member
I would speculate that the actual difference is very minimal. If you spray foam the ceiling you will be sealing up all the infiltration points that way. You will have to use the more expensive cans that allow direct application of foam and you will have a hell of a time if you ever want to change anything, but you may never need to change anything.
The volume of air in the attic isn't really important for heat loss, it is the surface area that matters. And yes, with a 12/12 pitch you will have significantly more surface area as compared to the flat ceiling. But at the same time that air in the attic will have an r factor. Don't know what it is but it might offset the added surface area of putting foam on the roof and not the ceiling.
In short, if you don't give a hoot about using your attic space (which with a 12/12 pitch would be a lot of great space in my opinion), and you are really confident that you have figured out all the wires and whatnot that you might want traversing your attic, then the cost savings of that much less foam is a no brainer.
And just to make you jealous, the Earth temp down here is 68 degrees a few feet down year round. No need to insulate that!
The volume of air in the attic isn't really important for heat loss, it is the surface area that matters. And yes, with a 12/12 pitch you will have significantly more surface area as compared to the flat ceiling. But at the same time that air in the attic will have an r factor. Don't know what it is but it might offset the added surface area of putting foam on the roof and not the ceiling.
In short, if you don't give a hoot about using your attic space (which with a 12/12 pitch would be a lot of great space in my opinion), and you are really confident that you have figured out all the wires and whatnot that you might want traversing your attic, then the cost savings of that much less foam is a no brainer.
And just to make you jealous, the Earth temp down here is 68 degrees a few feet down year round. No need to insulate that!
