Best ways to insulate a modified bitumen roof?

I've been wondering about this too. Gravel and slope seem straightforward enough, but does anyone know if skipping drainage mats affects insulation performance or longevity of the modified bitumen layer itself? Curious if there's data or experience on that angle...

I've skipped drainage mats before on a small flat roof project at my old place - figured gravel and slope would be enough. Honestly, insulation-wise, I didn't notice any real difference. But longevity... that's another story. After about five years, I started seeing some minor pooling and wear spots. Can't say for sure if mats would've prevented it, but looking back, I'd probably include them next time just for peace of mind.

I've seen similar situations quite a bit. Honestly, drainage mats aren't really about insulation - they're more about protecting your roof membrane and helping water move off efficiently. Had a client who skipped them once, thinking the slope would handle everything. Fast forward a few years, and he had some stubborn puddles forming... nothing catastrophic, but enough to annoy him every rainy season. Mats probably would've helped there. They're not magic, but they do add that extra layer of protection that's worth considering.

Good points all around. I've found the same thing - drainage mats aren't insulation per se, but they definitely help avoid headaches down the road. Had a similar issue with a building I manage; owner thought we'd be fine without mats because we had decent slope. Couple years later, we're dealing with those annoying puddles too. Nothing major, but enough for tenants to notice and complain occasionally. Mats probably would've saved us some hassle... hindsight, right? Anyway, good call mentioning it.

Had a similar experience myself - worked on a building where the owner insisted slope alone would handle drainage. It did...mostly. But after a few heavy storms, we started noticing those stubborn little puddles that just wouldn't dry out. Eventually, tenants started pointing out minor leaks and damp spots inside. Ended up retrofitting with mats later, which was pricier than doing it upfront. Definitely agree mats aren't insulation exactly, but they sure help protect your insulation investment long-term. Live and learn, right?