If underlayments could talk: which one would outlast the others?

I actually asked about that when we had our roof done last fall. Our contractor used cap nails on the synthetic, said it holds up better in wind than staples, especially since we get those crazy gusts off the lake. I’ve heard some folks say staples are fine if you use enough, but I wasn’t convinced. Has anyone noticed a difference in noise or leaks between felt and synthetic? Ours seems quieter during rain, but maybe that’s just me.

We had a similar debate at our place when we re-roofed a couple years back - our old felt underlayment was a mess after one bad winter, so I figured synthetic had to be worth a shot. Ended up going with synthetic and cap nails too, mostly because my neighbor’s roof actually lost a chunk of felt after a big storm (he’d used staples). Haven’t had any leaks since, and honestly, I think the noise is less noticeable during heavy rain compared to the old felt. Could just be my imagination, but it does feel quieter.

One thing I did notice: when we walked on the roof before the shingles went down, the synthetic seemed a lot less “crunchy” than felt. Maybe that’s why it sounds different in the rain? I’m curious if anyone’s seen how these synthetics hold up after 10-15 years - does it break down under shingles over time, or is it really as tough as they claim?

I’ve torn off a few roofs with synthetic underlayment that were 12-15 years old, and honestly, most of them looked almost new under the shingles - no weird brittleness or tearing like felt gets. That being said, I’ve seen some cheaper synthetics start to curl or get brittle if there’s a leak and water sits on them for months. The higher-end stuff seems to hold up better. Haven’t seen one totally fail yet, but I’d be curious what happens at the 20-year mark... might depend on how much sun sneaks in around the edges too.

I’ve seen the same thing with synthetics - they usually look way better than old felt, even after a decade or more. But I agree, the cheap stuff can go downhill fast if it gets wet. Around here (lots of sun), edges are always the first to go. Sometimes you’ll see shrinkage or curling where the underlayment’s exposed, especially if the drip edge isn’t tight. I’m curious too what 20+ years will look like... shingles usually give up first anyway.

I get where you’re coming from, but I’ve actually seen some of the newer high-temp felt underlayments hold up surprisingly well, even in spots with a lot of sun exposure. Synthetic does look cleaner, but if you’ve got a tight drip edge and good overlap, quality felt can still go the distance. The real killer seems to be improper installation - once water gets underneath, it doesn’t matter what you used. Edges and valleys always tell the story first...

- I’ve seen the same thing with felt - if it’s put down right, it can last way longer than people expect.
- Still kinda skeptical about felt vs. synthetic in spots where ice dams or standing water happen. Once moisture sneaks under, like you said, it’s game over.
- Anyone ever had issues with synthetic getting brittle after a few years in crazy heat? I hear mixed things but haven’t seen it myself yet...
- Curious if anyone’s compared how either holds up under metal roofs vs. shingles. Seems like the extra heat from metal would make a difference?

Curious if anyone’s compared how either holds up under metal roofs vs. shingles. Seems like the extra heat from metal would make a difference?

I’m wondering the same thing, honestly. We just bought a place with a metal roof and I keep picturing the attic turning into a giant toaster every summer. Is synthetic really up for that kind of heat, or does it just start crumbling like old crackers after a few years? I’ve heard felt can get weird and wavy if it gets wet, but synthetic seems like it could get brittle. Anyone ever peeked under a metal roof after a few years to see what’s actually happening?

- I’ve had both felt and synthetic under metal (in Texas, so it gets brutal).
- Synthetic held up better for me - no weird smells or crumbling after 6 years.
- Felt under an old shed roof got wavy and stuck to the metal in spots, especially where there was a leak.
- Metal definitely cooks the attic more than shingles, but the synthetic didn’t seem brittle - just dusty.
- Only thing: synthetic can get slippery if you’re up there working.
- Price-wise, synthetic was a little more upfront but didn’t need replacing as fast.
- Haven’t seen any cracking or major issues yet, but I do wonder how it’ll look after 15+ years...

I get the hype around synthetic, but I’m still not totally sold it’s the clear winner long-term.

“Haven’t seen any cracking or major issues yet, but I do wonder how it’ll look after 15+ years...”

Yeah, I’ve seen that brittleness too, especially if the synthetic sits out in the sun for a week or two. It’s like it just bakes. Felt isn’t perfect, but at least it doesn’t turn into a potato chip when you’re not looking.

That’s the thing with synthetics - they’re like vampires, just can’t handle the sun. I’ve had rolls that looked fine going down, then two weeks later they’re curling up like old bacon. But felt’s got its own quirks, right? I mean, one good storm and you’re chasing pieces across the yard. Ever tried picking up 30lb felt after a windy night? Not my favorite workout.

Still, I get what you mean about the potato chip effect. I’ve seen synthetic underlayment go from flexible to crispy in no time, especially in July. Makes you wonder if any of these underlayments would survive a Texas summer without drama. Maybe the real question is, which one annoys you less when things go sideways? I’ll take a little felt fuzz over brittle plastic shards any day, but ask me again after the next rainstorm and I might change my mind...

I’ll take a little felt fuzz over brittle plastic shards any day, but ask me again after the next rainstorm and I might change my mind...

I hear you on that. Last summer, I put down synthetic on my shed roof thinking it’d be less hassle. Looked great for about a week, then we hit a heatwave and it started curling up at the edges - almost looked like someone tried to peel it off. With felt, yeah, it’s heavier and a pain in the wind, but at least it doesn’t turn into confetti. If I had to pick, I’d rather wrestle with felt than sweep up plastic bits all over the yard. Neither is perfect, but at least felt gives you a fighting chance when the weather turns.

Funny, I thought synthetic was supposed to be the “set it and forget it” option, but I’ve had similar issues with curling and tearing. Maybe it’s just not cut out for the wild temperature swings we get here. Anyone ever try one of those peel-and-stick membranes? Curious if they actually hold up better or if that’s just clever marketing. My neighbor swears by them, but he’s only had his up for a year or so - hard to say long-term.

That’s interesting - synthetic was supposed to be the low-maintenance choice, but I’ve seen the same curling in spots where the sun hits hardest. The temperature swings here seem to mess with a lot of materials. I’ve managed a few properties where we tried peel-and-stick underlayment on tricky valleys and low-slope sections. It definitely went down easier, but after two winters, there was some edge lifting. Not as dramatic as the synthetic tearing, though. Maybe it’s a trade-off: easier install and decent short-term performance, but still not immune to our weather extremes. Anyone else notice that the warranties always sound better than what actually happens on the roof?

I get what you’re saying about warranties not matching real-world results. But I’ve actually had better luck with high-temp ice and water shield, especially on those south-facing slopes that just bake in the summer. It’s pricier and a pain to work with compared to synthetics or standard peel-and-stick, but it seems to hold its edges longer - less curling, even after a few freeze-thaw cycles. Maybe not perfect, but in spots where I know the sun and snow are brutal, it’s been worth the hassle. Curious if anyone else has seen that or if it’s just our weird microclimate...

I totally get the appeal of high-temp ice and water shield, especially with all-day sun exposure. But I actually went with a synthetic underlayment last year on my place (asphalt shingles, midwest winters), and it’s held up surprisingly well so far - no curling or leaks, even after some wild temperature swings. It was lighter and way easier to install, which mattered since I was doing most of it myself. Not sure if it’ll last as long as the pricier stuff, but for me, the trade-off in cost and effort made sense. Maybe it’s just luck or our less intense sun, but I’m curious if others have found synthetics to be a decent middle ground.

I’ve seen a lot of synthetic underlayments hold up well for a few years, but I’ve also inspected some roofs where they started to break down faster than expected - especially around fasteners or if there was any ponding. High-temp ice and water shield is definitely overkill for some climates, but in spots with a lot of freeze/thaw or sun, it really does seem to outlast the synthetics. The lighter weight is nice for DIY, though... just depends how long you want it to last before another round of repairs.

I went with synthetic underlayment last fall because I figured it’d be easier to handle on my own, but I’m already noticing some curling around the nails. Not sure if it’s a bad install or just the material, but I’m starting to wish I’d splurged on the ice and water shield, at least for the valleys. The lighter stuff is fine for now, but I don’t want to be up there patching things every couple years.

I hear you on the synthetic curling - ran into the same thing a couple years back, especially around fasteners. In my case, it was partly the material and partly not getting the nails flush enough. Ice and water shield in the valleys is definitely worth the extra cost if you’re worried about leaks. I’ve found the lighter synthetics are fine for most of the roof, but those tricky spots need something beefier or you’ll be patching more than you want.

Ice and water shield in the valleys is definitely worth the extra cost if you’re worried about leaks.

Couldn’t agree more, especially in storm-prone areas. I’ve seen too many repairs where skipping that step led to rot. One thing I’d add - when using synthetics, always double-check fastener placement and overlap at seams. Even the best material can fail if water finds a path underneath. For hips and valleys, I always go with a heavier ice and water product, even if it’s overkill elsewhere. It’s just not worth risking a leak where water naturally collects.