Actually you see more roofs in warmer climates being sprayed because of the insulating factor and top coat on the foam reflects more heat so it doesn't absorb into the house or building:U:

Well, hot blown insulation, at least around here, is limited as to how you can spray it by code. I don't remember the specifics, but for walls its one thickness (generally 3.5") for ceilings its another, and for rafters its another. Its a specialty, and few companies do it. But the ones who do know all the regs, so its best to talk to them and get a few quotes.

Not sure if is it hot or cold...

The roof rafters are 2X6", no walls. The bid says 5" nominal inches of Demilc Sealection 500 1/2# foam in all rafters of existing home.

Demilec USA

5" of sprayed in place 2 component polyurethane foam for 2 bucks a square foot? That's a great price if it is what I'm thinking. I use to spray polyurethane foam on Hotel roofs all over the country. I'm gonna have to go back and look at the link and get some more specifics of this product.