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

I get the appeal of synthetic, especially with how unpredictable contractors can be. I was skeptical about paying more, but after seeing how felt basically turned into mush during a rainy week, I’m leaning synthetic too. Still not sure it’s worth double the price, but the peace of mind is hard to put a number on. Maybe depends on your weather - felt might be fine if you’re in a drier spot?

Had a similar debate last year when we had to re-roof one of our duplexes. I was leaning toward felt because it’s what I’d always used, but after a surprise storm hit mid-project, the felt just didn’t hold up - got soggy and tore in spots. Ended up paying extra for synthetic on the next job. It stung a bit cost-wise, but not having to worry about rain delays or leaks was worth it for me. If you’re in a dry area, maybe felt’s fine, but anywhere with unpredictable weather... I’d lean synthetic, even if I grumble about the price.

We went with felt when we first moved in, mostly because it was cheaper and I figured it’d be fine for our mild winters. Regretted it after a windy rainstorm - had to patch up a few spots. If I had to do it again, I’d probably just pay extra for synthetic and skip the hassle.

Had a similar situation about five years back - went with felt on a low-slope roof, mostly because it was what the builder recommended and it kept the initial costs down. First year was fine, but after a couple of wind-driven rainstorms, I noticed water stains in the attic. Turns out, some of the felt had torn near the eaves where the wind gets under the shingles. Ended up patching it with more felt, but it never really sealed right after that.

Here’s what I learned: 1) Felt just doesn’t hold up well if there’s any chance of wind uplift or driving rain, especially on lower slopes. 2) Synthetic underlayment is lighter, lays flatter, and in my experience, doesn’t wrinkle up or tear nearly as easily. It costs more upfront, but I’d say it paid for itself in peace of mind (and fewer attic stains).

If you’re in a spot with even occasional storms, synthetic is just less hassle long-term. Only thing I’d double-check is whether your shingle manufacturer requires a specific type for warranty reasons - some are picky about that.

I hear you on the felt - my last place had a similar issue. I went with felt because it was cheaper and seemed like the standard, but after a couple of years (and some heavy spring winds), I started seeing those telltale brown stains in the ceiling corners. Turns out, the felt had shifted and torn near the ridge, probably from wind getting under the shingles just like you described.

Switched to synthetic on my current house, and honestly, it’s been way less hassle. It’s lighter, easier to install (even for someone not super handy), and I haven’t noticed any wrinkling or tearing even after a few nasty storms. The upfront cost was maybe $200 more for my roof size, but considering what I spent patching leaks before, it’s worth it.

Only thing I’d add is that not all synthetics are created equal - some of the really cheap stuff can be slippery or hard to nail down. Also, if you’re trying to keep costs down, sometimes local supply houses have sales on better brands if you’re not in a rush... just something to watch for.

Only thing I’d add is that not all synthetics are created equal - some of the really cheap stuff can be slippery or hard to nail down.

That’s been my gripe with synthetic too. Some brands are almost like plastic tarps - super slick, especially on a hot day. Did you notice any difference in how it handled moisture during install? I’ve seen felt soak up rain and wrinkle, but not sure if the cheaper synthetics do any better.

I’ve run into the same thing with some synthetics - especially the bargain bin stuff. A few brands are so slick you feel like you’re ice skating up there, and it’s even worse on a steep pitch or when the sun’s beating down. I get why folks still like felt for grip, even if it’s a pain when it wrinkles.

On moisture, I’ve noticed felt definitely soaks up water and then you get those waves and bubbles as it dries out. That’s a headache if you’re trying to keep things flat for shingles. The cheaper synthetics don’t absorb water, but I’ve seen some puddle up and then you get little pools sitting until the sun dries them off. The higher-end synthetics seem to shed rain better and stay tight, but yeah, price is a factor.

For installs that get rained on mid-project, I’d rather deal with a good synthetic than felt, just because it doesn’t turn into mush or fall apart. On the other hand, I’ve seen some of the really thin synthetics tear if you’re moving ladders or dragging bundles around - felt usually holds up better in that situation. It’s kind of a tradeoff.

Curious if anyone’s had issues with synthetic underlayment getting brittle over time? I’ve peeled back old roofs before and some of those early synthetics basically turned to potato chips after a decade in the sun. Wondering if the newer stuff holds up any better long-term, especially in hotter climates.

I get the point about cheap synthetics being slippery - had a buddy nearly take a tumble on one of those “ice rink” brands last summer. But I’m not totally sold on the idea that higher-end synthetics are always worth the extra cash, especially for folks like me trying to keep costs down.

“The higher-end synthetics seem to shed rain better and stay tight, but yeah, price is a factor.”

That’s my hang-up. I’ve used felt on a couple of smaller projects and yeah, it wrinkles if it gets wet, but it’s cheap and easy to replace if something goes wrong. The synthetic stuff I can afford is usually the thinner kind, and I’ve had it tear just from moving a ladder, like you mentioned.

As for long-term durability, I’ve seen both felt and synthetic look pretty rough after 10-15 years, especially in hot weather. Not sure if the newer synthetics are really that much better - manufacturers always claim their latest version is “UV stable,” but who knows until it’s been up there a decade or more?

Is it really worth paying double or triple for premium synthetic if you’re just planning to re-roof in 15-20 years anyway? That’s where I get stuck.

Is it really worth paying double or triple for premium synthetic if you’re just planning to re-roof in 15-20 years anyway?

I’ve wondered the same thing, honestly. On my uncle’s place, we used basic felt under some old three-tabs and yeah, it wrinkled after a heavy rain but flattened out once the shingles went on. He got 18 years out of that roof before any issues. I’ve seen the “UV stable” synthetics get brittle and tear up here in Texas sun too, so I’m not convinced they’re always worth the markup unless you need a long exposure window or have a super low slope. For most regular jobs, felt seems fine if you’re watching your budget.

I get where you’re coming from. I went with felt on my place last year because the price difference was wild, and I figured if it lasted 15-20 years, that’s good enough for me. Haven’t had any issues so far. Sometimes simple just works.

Sometimes simple just works.

That’s been my motto for years, honestly. I went with felt too - mainly because my dad swore by it and, well, he was usually right about this stuff. But I keep hearing folks rave about synthetic being lighter and easier to install. Anyone actually notice a difference with heat in the attic or is that just marketing fluff?

I’ve wondered about the heat thing too. My neighbor switched to synthetic last year and swears his attic feels cooler, but I’m not sure if that’s just because he finally added some insulation up there. I’ve only ever used felt - old habits die hard, I guess. Anyone notice if synthetic actually holds up better after a few years, especially in places with wild temperature swings?

I’ve seen a lot of claims about synthetic underlayment making attics cooler, but honestly, most of the time it’s the insulation or ventilation doing the heavy lifting there. Synthetic does tend to resist tearing and UV damage better than felt, especially if your roof sits exposed for a while before shingles go on. But in places where temps swing from freezing to blazing hot, I’ve noticed some synthetics can get brittle over time - depends a lot on the brand and thickness. Has anyone actually pulled up old synthetic after 5+ years to see how it compares to felt in real-world conditions? I’m curious if the adhesives or coatings start to break down with all that expansion and contraction...

I’m right there with you on the insulation and ventilation being the real game changers for attic temps. I’ve heard the same marketing pitch about synthetics keeping things cooler, but honestly, I think that’s a stretch. What I do like about synthetic is how much easier it is to work with - lighter, less messy, and it doesn’t wrinkle up like felt if it gets damp before shingles go on.

But yeah, the long-term durability is still kind of a question mark for me too. My neighbor had his roof redone about six years ago with synthetic (not sure which brand), and when he had a small section opened up after a tree limb fell, the underlayment looked fine - no cracking or peeling. That said, we’re in a milder climate, so maybe not the best test case.

I get what you’re saying about brittleness in extreme temps. Some of the cheaper synthetics feel almost plasticky and I’d worry about them getting brittle after years of freeze/thaw cycles. Felt isn’t perfect either though - it can dry out and turn to dust if there’s any moisture intrusion. Honestly, I wish there was more real-world data out there instead of just manufacturer claims...

The six-year inspection you mentioned is encouraging, but I’d be careful about treating “synthetic” as one category. The useful comparison is the product data sheet: permitted UV exposure time, minimum and maximum installation temperatures, and whether the warranty changes once it’s left uncovered.

A product rated for 30 days in direct sun isn’t equivalent to one rated for 90, and a thin budget membrane may behave very differently from a heavier, high-temperature version. The same goes for freeze/thaw claims. Has anyone compared those specifications for the actual brands used in Texas or other extreme climates, rather than relying on general claims that synthetic resists UV and heat better?