But for those who’ve had both, does felt hold up any better if your venting isn’t perfect, or does it fail just as fast?
Honestly, I’ve seen both types take a beating when attic ventilation’s not right. Synthetic’s supposed to be tougher, but like you said, it’ll curl up and look sad if the heat’s trapped up there. Felt, on the other hand, just kind of dries out and gets brittle. I had a spot above a bathroom where the vent fan wasn’t hooked up right—felt underlayment basically turned into a potato chip after a couple summers. Not pretty.
I wouldn’t say felt “holds up” better, but it might fail differently. Synthetic tends to peel and let water sneak in, while felt just sort of disintegrates. Either way, without good airflow, both are gonna have a rough time. Midwest summers can cook an attic like a slow-cooker, so venting’s probably more important than underlayment type.
Curious if anyone’s tried those fancy “breathable” synthetics? I keep hearing about them but haven’t seen one in the wild yet...
That’s interesting about the felt turning brittle—I figured it’d just get soggy, not crispy. Has anyone noticed if one type smells worse than the other when things get hot and stuffy? My attic gets pretty toasty in July, and I swear I can smell tar sometimes...
I’ve actually had the opposite experience with felt—mine didn’t get soggy or brittle, but it did start to stink when the attic heated up. I’m in central Texas, so July and August are brutal. That tar smell you mentioned is real, especially if you’ve got traditional 15 or 30 lb felt. It’s not overwhelming, but it’s definitely there on hot afternoons.
I switched to synthetic underlayment last time I re-roofed, mostly because it was only a bit more expensive and supposedly lasts longer. Haven’t noticed any weird smells since then, even when the attic hits 120°F. The synthetic stuff doesn’t seem to off-gas like felt does, at least not that I can tell.
One thing though—synthetic can be slippery if you’re doing any work up there yourself. Not a dealbreaker for me, but worth mentioning. If you’re sensitive to odors or just want less mess in the long run, synthetic might be worth the extra cost upfront. Felt’s cheaper, but I’d rather avoid that tar smell if I can help it...
That tar smell is no joke—my buddy calls it “attic barbecue” season. I totally get wanting to avoid it, especially in Texas heat. I’ve slipped on synthetic before, so yeah, it’s like walking on a greased-up slip-n-slide if you’re not careful. But honestly, not having to deal with that sticky, smelly mess is a win in my book. Did you notice any difference in how the shingles lay over the synthetic? I’ve heard some folks say it feels stiffer, but maybe that’s just me being paranoid...
I’ve wondered about that “stiffer” thing too. When I helped my neighbor redo his roof last year, we used synthetic and yeah, it didn’t hug the deck like felt does. The shingles seemed to sit a little higher, but once everything was nailed down and baked in the sun for a week, I honestly couldn’t tell much difference. Maybe it’s just that first day or two? Also, is it just me or does synthetic seem louder when you walk on it? My dog hated the crinkling noise...