The whole system has to work together or you’re just throwing money at the wrong spot.
That’s the part I keep coming back to. I’ve had a couple roofs where we used top-tier synthetic underlayment, but the attic ventilation was a mess—ice dams every winter, and the underlayment didn’t save us from leaks. Has anyone actually seen a felt underlayment outlast synthetic in real-world conditions? Or is it always the airflow and insulation that make or break it? I’m curious if there’s ever a scenario where felt would “win” that race, or is it just outdated at this point?
Has anyone actually seen a felt underlayment outlast synthetic in real-world conditions? Or is it always the airflow and insulation that make or break it?
I’ve wondered the same thing after watching a few “old school” roofs get torn off around here. I’m in upstate NY, so we see our fair share of ice dams and wild temperature swings. The funny thing is, my uncle’s house still had the original 30-lb felt from the late ‘70s under his shingles when they finally re-roofed last year. It was brittle as heck but somehow still hanging on in spots. But the rest? Swiss cheese from leaks where venting was poor and insulation was basically nonexistent.
Honestly, I’ve never seen felt win against synthetic when you look at everything side by side—unless you count those weird edge cases where the felt just happened to be installed perfectly and the attic was bone dry, which almost never happens. Synthetic seems to handle our wet springs better too. I’ve been on jobs where rain hit before we could shingle, and the synthetics shrugged it off while felt would have turned into mush.
But yeah, I totally agree with what you said about airflow and insulation being the real deal-breakers. You can spend all you want on fancy underlayment, but if your attic’s basically a sauna in winter or your soffit vents are blocked by old insulation, none of it really matters. The roof’s just gonna sweat and rot from the inside out.
I do get why some folks stick with felt—maybe it’s habit or cost or just liking what they know—but every time I see a manufacturer’s warranty on synthetic that’s like 20+ years, it’s hard to argue for felt unless you’re doing a super quick patch job.
Long story short: I haven’t seen felt outlast synthetic unless everything else was perfect...and let’s be real, how often does that happen?
Long story short: I haven’t seen felt outlast synthetic unless everything else was perfect...and let’s be real, how often does that happen?
That’s pretty much what I’ve noticed too. I’ve only been around the trade a couple years, but every time we pull up old felt it’s either totally shot or just barely hanging on in the dry spots. The only time it looked halfway decent was on a steep roof with killer ventilation—like, you could see daylight through the soffits and ridge vent. But even then, the felt was brittle and tore up easy.
I get why some folks still use felt, especially for quick repairs or if they’re used to working with it. It’s cheap and you can grab it at any supply house. But after seeing how synthetic holds up when it rains before shingling, I’m not sure why anyone would go back unless they’re pinching pennies. We had a job last fall where we got caught by a surprise storm—synthetic underlayment didn’t even flinch, but the spot we patched with felt (ran out of synthetic) turned into a soggy mess overnight.
One thing I’m still trying to wrap my head around is how much difference insulation and airflow actually make. Like, you can have the fanciest underlayment in the world, but if your attic’s packed with old insulation blocking the vents, you’re just asking for trouble. I’ve seen more rot from bad ventilation than anything else.
I do wonder if there are places where felt actually makes sense long-term—maybe somewhere super dry? Around here (midwest), with all the freeze/thaw and humidity swings, synthetic just seems safer. Maybe if you’re doing a historic restoration and want to keep things original, but otherwise... hard to argue against synthetic these days.
Curious if anyone’s actually seen a modern felt job last 20+ years without issues? Or is that just wishful thinking?
I’ve torn off a lot of roofs after storms and honestly, felt just doesn’t hold up unless everything else is dialed in perfectly. Even then, it’s a gamble. I get the nostalgia or budget angle, but synthetic’s saved my bacon more than once when weather turned ugly mid-job. Has anyone actually seen felt outperform synthetic after a major wind event? I haven’t, but maybe there’s some unicorn out there…
- Gotta admit, I’ve seen felt try to hang in there, but it’s like watching a turtle in a greyhound race.
- Synthetic’s definitely got the edge when the wind picks up—felt just kind of waves the white flag and peels off.
- Had a neighbor swear by old-school felt, but after last spring’s windstorm, his underlayment was halfway to Kansas. Meanwhile, my synthetic stuff barely budged.
- Only time I saw felt “win” was on a tiny shed that never sees more than a stiff breeze... not exactly a fair fight.
- Curious if anyone’s tried those recycled or eco-friendly synthetics? Wondering if they hold up as well as the regular stuff or if they’re just green marketing.
- At this point, I’d only use felt if I was desperate or doing a quick patch job. Otherwise, synthetic’s my go-to—less stress when the forecast looks sketchy.
Anyone actually had luck with those new plant-based underlayments? Or is that just another unicorn?