Which holds up better over time: felt or synthetic underlayment?

I hear you on synthetic being easier to work with, but I’ve actually seen a few cases where it didn’t perform as well as expected after hail storms.

“No underlayment is gonna save you from a bad install or a big ice dam.”

That’s spot on, but I’d add - after a major storm, felt sometimes absorbs just enough moisture to show you where the leaks are, while synthetic can let water run and hide the problem until it’s worse. Not saying felt’s perfect, but in storm-prone areas, it’s worth considering how repairs play out down the line.

I get what you’re saying about felt showing leaks, but in my experience, that’s a double-edged sword. Last winter, after a nasty windstorm, I found out the hard way - my old felt underlayment soaked up enough water to start sagging between rafters. By the time I noticed, the decking was already starting to rot. With synthetic, at least the water would’ve run off before causing that kind of damage... or at least that’s what I’m hoping for with my new roof. Maybe it depends on how quickly you can get up there and check things after a storm?

With synthetic, at least the water would’ve run off before causing that kind of damage... or at least that’s what I’m hoping for with my new roof.

I hear you on the felt sagging - seen it more than once after a wet winter. Synthetic does shed water better and won’t go mushy like felt, but I’ve also had cases where a bad install meant water got underneath anyway. If your shingles blow off and the synthetic’s not sealed right, you can still get leaks, just maybe not as obvious at first. Quick checks after storms help, but sometimes life gets in the way... For my own place, I switched to synthetic too, mostly for peace of mind during long stretches between repairs. Just don’t forget to check those fasteners if you’re in a windy spot.

Funny timing - my neighbor just swapped his old felt for synthetic last fall, and he’s been bragging about how “high-tech” his roof is now. But a month ago, we had one of those sideways rainstorms, and sure enough, a couple shingles peeled up. He found out the hard way that synthetic doesn’t mean invincible... Water still snuck in at the seams where the installer got lazy with the overlap. It’s almost like these new products make us feel a little too safe sometimes?

I totally get why people are moving away from felt, though. On my own place (asphalt shingles, pretty standard ranch in central NC), the felt turned into this lumpy mess after a few years - looked like someone stuffed old towels under there. And once it gets soggy, it’s game over. Synthetic definitely holds up better in our humidity, and I like that it’s lighter to haul up a ladder (my knees thank me every time).

But I do wonder: does anyone else worry about the plastic waste? I’ve been looking into some of the “greener” synthetics they’re making now, but I haven’t found one that really seems both tough and eco-friendly. Or maybe I’m just overthinking it... Hard to ignore all that plastic when you’re trying to be more sustainable.

Anyway, I check my roof after every big wind event now - fasteners can work loose even on synthetic, especially with those gusts we get in spring. It’s not a perfect system, but at least the underlayment isn’t turning into oatmeal anymore. Has anyone tried any recycled-content synthetics or even something wild like hemp fiber underlayment? Just curious if there’s a middle ground between durability and not trashing the planet.

One last thing - has anyone had luck getting insurance to cover underlayment upgrades after storm damage? My adjuster acted like anything beyond basic felt was “fancy stuff.” Maybe they just don’t want to pay for it...

That’s a good point about the “invincible” feeling with synthetics. I’ve seen that too - folks assume the newer materials will cover for bad installation, but like you said, “

Water still snuck in at the seams where the installer got lazy with the overlap.

” Attention to detail is still everything.

I do share your concerns about plastic waste. Some of the recycled-content synthetics are promising on paper, but I haven’t seen one yet that holds up as well as the mainstream stuff, especially on low-slope roofs or in high UV areas. Hemp fiber underlayment sounds interesting, but I’d be nervous about longevity in our climate.

Insurance-wise, it’s hit or miss. Most carriers here just want to pay for basic felt unless you can prove code requires something else after storm damage. You really have to push back and document every step if you want an upgrade covered.