We had a quote done a few years ago, 5k for about 2000 sq ft house. It's not much better than standard rockwool style insulations though, and installers won't add standard insulation to it either if you decide later that it's not doing a good enough job (either due to bugs and mice eating it, or degrading over time). It's one of those "you're stuck with it" things.
@TinkerTanker why won't they add blow-in insulation? 
I'm no expert on this, but if they spray-on closed-cell insulation on the bottom of the roof decking - then any moisture is trapped in the decking. Trapped moisture could lead to decking rot.
For the people that have sprayed-on insulation (closed cell) on the roof deck - any signs of problems after 10 years?
For the people that have sprayed-on insulation (closed cell) on the roof deck - any signs of problems after 10 years?
I can't remember if it voids the warranty or there's a chemical interaction between the two. In any case the installers won't do it. And if they replace the roof decking (which they have to do every few years) it's a pain for the roofers too. More charge.@TinkerTanker why won't they add blow-in insulation?
You could always carry it up there yourself I guess, but cost vs benefit we went with Safe & Sound sound deadener/insulation
https://www.lowes.com/pd/ROCKWOOL-S...-4382951-_-Online-_-0-_-0&gclsrc=ds&gclsrc=ds
That's some pricey stuff! 
One draw back is the asphalt shingle mfgs. were wiggling out of warranty issues claiming the foam retained
or trapped excessive heat and that it promoted deterioration of shingles. That was years ago though.
or trapped excessive heat and that it promoted deterioration of shingles. That was years ago though.
A cousin of mine experimented with spray on insulation and what is called blue board down in SE states. He did a wood frame roof, 1/2 spray in and 1/2 blue board. He determined over time the spray in due to humidity caused moisture to collect in the decking leading to rot. The blue board didn't experience the same issue. It was cut to fit tightly between rafters. R value was a little less than spray in but no issues over time. Both were pest attractions burrowing into it to make their homes but with pesticides they were controlled.
PS: This was done many years ago so material composition today may differ and have differing results.
PS: This was done many years ago so material composition today may differ and have differing results.
@swampratt We did closed cell foam spray on the bunkhouse at our property but it's a pole barn design with metal sides and roof. A 24'x36' was $3800 about 2 years ago for all sides(14') and roof. I can send pics if that's something you're interested in seeing.
12 years here, was sprayed on when the house was built. Just had the asphalt shingles replaced and no sign of any decking rot or other problems.
