I’ve managed a few buildings where we switched to synthetic underlayment, and honestly, I’d never go back to felt. The breathability debate is real, but in practice, most attic moisture issues I’ve seen come down to air leaks from the living space, not the underlayment itself. Peel-and-stick ice barriers are a must for the first few feet if you get ice dams—saved us a headache more than once. For early moisture detection, I swear by cheap humidity sensors in the attic and just poking my head up there every couple months. If it smells musty or feels damp, something’s off.
I had no idea about any of this stuff until I bought my house last year and suddenly found myself googling “why does my attic smell like a wet dog?” Turns out, it was a combo of bad bathroom fan venting and some ancient felt underlayment that looked like it’d been through a few world wars. I swapped in a humidity sensor after reading about it here—honestly, best $12 I’ve spent. Still not sure about synthetic vs felt, but anything that keeps me from crawling around up there more than twice a year is a win in my book.
I swapped in a humidity sensor after reading about it here—honestly, best $12 I’ve spent. Still not sure about synthetic vs felt, but anything that keeps me from crawling around up there more t...
That “wet dog” attic smell brings back memories. I once opened up a roof and found layers of felt so brittle it crumbled like old newspaper. I’ve switched to synthetic underlayment for most jobs now—less mess, lighter to haul up, and it doesn’t soak up moisture the way felt does. Still, some old-timers swear by felt, especially in colder climates. Funny how much you learn just trying to avoid crawling around in itchy insulation...
Had the same debate with myself a couple years back when I was patching up the old ranch house. The attic stank like wet socks after a rain, and the felt underlayment was basically mulch at that point. I ended up going with synthetic, mostly because hauling those lighter rolls up a ladder is way easier on my back. Haven’t noticed any moisture issues since, but I do wonder if it makes a difference in the winter—some folks around here still swear felt “breathes” better in deep cold.
Funny thing is, I never thought much about how shingles actually overlap until I watched my neighbor’s roof get replaced. Those guys laid them out just like fish scales, and it finally clicked why you can lose a few and not see leaks right away. Still, nothing makes you appreciate a good underlayment like crawling through blown-in insulation to chase down a drip in February. If I never have to do that again, it’ll be too soon...
Watching those shingles go on really does make the whole system make more sense. I’m curious—did you notice any difference in attic temps or humidity after switching to synthetic? I’ve heard some folks say it makes things warmer in winter, but not sure if that’s just talk.