Spray Foam Roofing vs Modified Bitumen (Torch-Down) for Flat Roofs
I have a flat roof building that is getting a new solar array and considering replacing the existing 12 year old roofing while I can. The two contenders are a spray foam roofing system that reportedly seals and insulates or another modified bitumen system that is torched down to seal. There’s a lot of posts on the forum about spray foam insulation but I haven’t seen anyone discuss this type of roofing.
Any thoughts and experience appreciated.
Replies
In my opinion, spray foam roofing is close to being a scam. It does work but it's up to you to keep it sealed. Because it's got a rough texture it mildews really badly then needs to be bleached and pressure cleaned before it's painted. Pinholes in the coating will let water in where it never dries out, only gets worse until you have rot everywhere. I've seen a lot of foam roofs but I've never seen one that lasted.
Do Not Use Foam, if you look at the application instructions for a foam roof the ambient humidity needs to be less than 20%. So regionally they can be viable, but in most areas the first reply is correct the foam warranty is for the foam and not the coating, but the coating is a “maintenance item.”
As far as the mod bit, it is a good roof, but the devil is really in the pipe flashings, I would urge you to find a roofer that has a sheet metal shop to fabricate custom 2 piece copper Sleeves and solder them in place. Alternatively, 2 part urethane adhesives and fabric (siplast and JM both offer systems) are quite effective. Here is an example of the siplast parapro https://youtu.be/WAv994TfghU