Spray foam costs $35,000–$40,000 to install on a 5,000 sq ft roof versus $60,000–$65,000 for modified-bitumen SBS. Over 20 years, spray foam needs one $20,000 recoating while SBS requires a full $65,000 replacement, making spray foam significantly cheaper. Spray foam also adds R-9 insulation for energy savings.
So over 20 years, the cost of an SBS roof versus a spray foam roof— say for example you had a 5,000 square foot roof— SBS on the low end is going to be $60,000-$65,000. On the high end, it could be way more than that. Spray foam for that same roof is going to be $35,000-$40,000. So the spray foam will need to be recoated in, say, 10 to 13 years. That's only going to cost you maybe $20,000. So the cost there is already just the cost of doing an SBS roof one time. So the second time you need to do your SBS roof in 20 to 25 years, it's gonna be another minimum $65,000. So as you can see, over time, the spray foam roof is a much cheaper system. It's a maintained system, and it's giving you energy savings at the end of the day because it adds an R-9 to your roof.
