- Had similar issues with mine, insulation depth wasn't the main culprit.
- Turned out ventilation was actually too restricted... adding more vents helped way more than extra insulation.
- Might wanna double-check airflow before piling on more insulation.
Interesting point about ventilation... hadn't really thought about airflow being such a big factor on modified bitumen roofs. I always assumed insulation was the main player since that's what everyone seems to talk about. But now that you mention it, it kinda makes sense—if the air can't move around properly, moisture buildup could definitely cause issues no matter how thick your insulation is.
I remember working on a job last summer where the homeowner kept piling on insulation thinking it'd solve their condensation problems. We spent days adding layers, and guess what? Didn't help one bit. Eventually, one of the senior guys suggested checking the vents. Turns out, half of them were blocked by debris and old roofing materials from previous repairs. Once we cleared those out and added a couple extra vents, things improved dramatically. The homeowner was pretty surprised (and maybe a little annoyed they'd spent so much on insulation first, haha).
Still, I wouldn't completely dismiss insulation depth as irrelevant. Seems like it's probably a balance between proper insulation and good airflow. Maybe it's worth checking both before committing to one solution? Curious if anyone else has had similar experiences or found other unexpected culprits causing issues with modified bitumen roofs...
Fair points raised, but I'd caution against overemphasizing ventilation as a universal fix. I worked on a project where the vents were perfectly clear, airflow was textbook-perfect, yet condensation persisted. Turned out the vapor barrier was improperly installed—moisture was seeping up from below. So yeah, airflow matters, but sometimes the problem runs deeper... worth checking all layers before assuming it's just vents or insulation depth alone.
Good point—seen similar issues myself. Couple quick thoughts:
- Modified bitumen roofs can be tricky. If condensation is persistent, definitely check the vapor barrier first. A lot of times, that's the real culprit.
- Insulation-wise, closed-cell spray foam under modified bitumen has worked well in my experience. It doubles as insulation and a solid vapor barrier.
- Another option: rigid foam boards (polyiso) installed correctly, taped seams and all, can really help control moisture.
- Ventilation is important, but like you said, it's not everything. Had a project once with textbook-perfect airflow too... still had moisture problems until we fixed the barrier underneath.
- Bottom line, always inspect the whole roof assembly carefully—layers matter, details count.
Yeah, closed-cell foam is great stuff but man, the cost adds up quick. I've had decent luck with polyiso boards myself—just gotta be meticulous taping those seams. Learned that the hard way... moisture finds every little gap.
