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

I’ve seen a lot of roofs in humid climates, and honestly, synthetic does seem to hold up better over time - especially against UV and moisture. But you’re right, it’s not perfect. I’ve noticed some synthetics don’t breathe as well as felt, which can be a problem if your attic isn’t vented properly. Mold under synthetic isn’t common, but I have seen it when there’s poor airflow. Haven’t run into many hybrid installs yet - most folks around here stick with one or the other.

I get what you’re saying about synthetics holding up better, especially with UV and moisture. But I’ve actually had the opposite experience on my last house (asphalt shingles, Gulf Coast). The synthetic underlayment was supposed to be the upgrade, but after about 8 years, I started noticing some weird bubbling and a musty smell in the attic. Turned out there was condensation trapped underneath because the synthetic just didn’t let things breathe like felt did on my previous roof.

I’m not saying felt is perfect - definitely had some issues with tearing during install and it doesn’t last as long exposed. But in terms of letting moisture escape, especially in a super humid climate, I feel like felt still has an edge if your ventilation isn’t top-notch. Anyone else run into condensation issues with synthetic? Or maybe it’s just a problem with certain brands or install methods...

- Seen this a few times, especially in humid spots like the Gulf Coast.
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“the synthetic just didn’t let things breathe like felt did on my previous roof.”

I’ve seen those “plastic tarp” synthetics fail fast, especially after a big storm rolls through - just shredded. But I’ll take a good synthetic over felt any day for wind resistance and walkability, as long as it’s one of the breathable types. The trick is, like you said, making sure attic ventilation isn’t an afterthought. I’ve torn off roofs where the cheap synthetic basically trapped a swamp underneath. Felt’s more forgiving with moisture, but it’s a pain if you get rain mid-job. Curious if anyone’s had luck with those hybrid underlayments that claim to combine the best of both?

I’ve been weighing this exact thing for a while, especially since I’m trying to stretch every dollar on my roof replacement. My house is in the Midwest, so we get a mix of heavy rain, snow, and the occasional windstorm. I’ve had felt on my old roof for years, and honestly, it did okay - except for the times when a sudden downpour hit mid-project and the felt just turned into a soggy mess. That was a nightmare to deal with, and it definitely slowed things down.

When I started looking into synthetics, I noticed the price difference right away. The cheaper ones felt almost like plastic tablecloths, and I’ve seen those rip up after a bad storm, just like you mentioned. But the higher-end synthetics seem sturdier and are supposed to be more breathable. I’m still a little skeptical about the “breathable” claims, though. I’ve read some reviews where people said their attics got musty after switching to synthetic, but I wonder if that’s more about poor ventilation than the underlayment itself.

I haven’t tried the hybrid underlayments yet, but I did get a sample from a local supplier. It’s thicker than the basic synthetics and has a felt-like texture on one side. The rep claimed it combines the moisture forgiveness of felt with the durability of synthetic, but I’m not sure how much of that is marketing. Has anyone actually installed one of these hybrids and noticed a difference in how the attic “breathes” or how it holds up after a year or two?

One thing I’m still trying to figure out is whether it’s worth paying extra for the hybrid, or if I should just invest in better attic ventilation and stick with a mid-range synthetic. If anyone’s done a cost breakdown or has long-term experience with the hybrids, I’d love to hear how it played out. Did it actually save money or hassle in the long run, or was it just another layer of expense?

I’m in a similar boat, trying to make sense of all the options without just throwing money at the problem. I get what you’re saying about the “breathable” claims - seems like every product is “the best” if you listen to the sales pitch. I’ve only had felt on my place (asphalt shingles, pretty standard), and it’s held up okay, but I did have a leak last winter after some ice damming. Not sure if that was the felt or just bad luck.

The hybrid underlayment thing is interesting, but I keep wondering if it’s really worth the extra cost, especially since I’d rather put that money into better attic vents or even insulation. Has anyone actually noticed a difference in energy bills or moisture issues after switching underlayment types? Or is it more about peace of mind than real-world results? Sometimes I feel like these upgrades are just another way for suppliers to upsell us... but maybe I’m being too cynical.

Sometimes I feel like these upgrades are just another way for suppliers to upsell us... but maybe I’m being too cynical.

I get the skepticism, but in my experience after a few major storms, synthetic underlayment actually does outperform felt - especially when it comes to tear resistance and water holdout if shingles blow off. Energy bills? Not much difference there, honestly. But for long-term durability, synthetics aren’t just hype. The real gains are in how they handle wind-driven rain and how they don’t wrinkle or degrade as fast as felt when exposed. If you’re in an area with wild weather swings, that extra cost can pay off by preventing bigger headaches down the line.

Had a job last year where we replaced a 15-year-old roof - original felt underlayment, and after a couple of windstorms, it was basically shredded under the missing shingles. We switched to synthetic for the replacement, and I’ll admit, I was a bit skeptical about the cost difference at first. But seeing how it held up during a surprise downpour mid-project, I get why folks are leaning that way now. Still, if you’re in a mild climate and budget’s tight, felt can do the trick... just don’t expect miracles if the weather turns nasty.

Felt’s like that old raincoat you keep in the trunk - fine for a drizzle, but you wouldn’t want to trust it in a hurricane. I’ve seen synthetic underlayment take a beating and still keep the deck dry, especially when storms roll in mid-job. It’s pricier, sure, but if you’re anywhere with wild weather swings, it’s worth it. That said, I’ve patched up plenty of felt roofs that lasted a decade or more in milder spots... just depends how much risk you’re willing to take.

That’s a good analogy with the raincoat - made me laugh a bit. I’m in the northeast, so we get everything from heavy snow to summer downpours, and honestly, I’m still trying to figure out what’s overkill versus what’s necessary. My inspector mentioned that synthetic underlayment is less likely to wrinkle or tear if it sits exposed for a while, which seems pretty important if there are delays during installation.

“I’ve seen synthetic underlayment take a beating and still keep the deck dry, especially when storms roll in mid-job.”

That part stood out because I worry about those unexpected storms mid-project. But then again, the price difference isn’t small. Has anyone noticed if synthetic actually helps with things like ice dams or long-term moisture issues under asphalt shingles? Or is it mainly about short-term protection during the build? I’m not sure if it makes a difference once the shingles are on and everything’s sealed up.

I’ve had both felt and synthetic underlayment on different roofs over the years (asphalt shingles, northeast climate - lots of freeze/thaw cycles, heavy snow, and the occasional sideways rain). From what I’ve seen, synthetic definitely shines when it comes to exposure during installation. I had a project delayed by almost two weeks due to a surprise nor’easter, and the synthetic held up without any leaks or wrinkling. Felt would’ve been a mess in that situation.

Once the shingles are on, though, I’m not convinced there’s a huge difference in day-to-day performance. The underlayment is really just a secondary barrier at that point. For ice dams, the bigger factor seems to be whether you have proper ice & water shield along the eaves and valleys, plus good attic ventilation. I haven’t noticed synthetic underlayment making a noticeable difference with ice dam issues - if warm air’s leaking into the attic and melting snow, you’ll get ice dams no matter what’s underneath the shingles.

Long-term moisture? Maybe synthetic resists rot and mold a bit better if water does get under the shingles, but if you’re seeing that kind of chronic moisture, there’s probably a bigger problem with the roof design or ventilation. I will say synthetic is lighter and easier to handle, especially on steeper pitches, but the cost is definitely higher. I guess it comes down to how much peace of mind you want during installation versus after everything’s buttoned up.

Curious if anyone’s actually had a roof leak years down the line where the underlayment made a difference? Or maybe someone’s seen felt break down faster under shingles in our climate? I’ve only replaced roofs after 20+ years, so hard to say if the underlayment was ever the weak link...

Curious if anyone’s actually had a roof leak years down the line where the underlayment made a difference? Or maybe someone’s seen felt break down faster under shingles in our climate?

I’ve torn off a couple old roofs around here (central MA, so similar weather) and the felt underlayment always looked like it’d been through a war zone. Brittle, torn in spots, sometimes even stuck to the decking like old gum. But honestly, the leaks I found were always traced back to bad flashing or ice damming, not the felt itself giving up. One time I did see mold between the felt and the wood, but that attic was basically a sauna - zero ventilation.

Synthetic definitely feels more “space age” when you’re rolling it out. Last summer I helped on a roof where we left synthetic exposed for almost a month (thanks, rain delays), and it was totally fine. Can’t imagine felt surviving that.

But yeah, once the shingles are on, I don’t know if it really matters unless you’ve got bigger issues. If you’re seeing chronic leaks, probably time to look at the attic or the gutters before blaming the underlayment.

That’s interesting about the mold - makes me wonder how much attic ventilation really factors in compared to underlayment type. I’ve always heard that synthetic is supposed to last longer, but I’m not sure if that’s just marketing or if anyone’s actually seen it hold up better after, say, 20 years under shingles. Has anyone done a tear-off where synthetic was used and could see the difference firsthand?

I’m in a similar climate (southern NH), and my last roof had 15# felt. After 18 years, the felt was basically dust in some spots, but the decking was still solid. No leaks except where ice dams backed up, which I guess is more about insulation and ventilation than what’s under the shingles. I’m leaning toward synthetic for my next roof just for the peace of mind if there’s a delay, but I keep wondering if it’s worth the extra cost long-term, or if it’s just insurance for the install phase.

Anyone ever had warranty issues where the underlayment type actually mattered? Or is it really just about what happens before the shingles go on?

my last roof had 15# felt. After 18 years, the felt was basically dust in some spots, but the decking was still solid.

That’s almost exactly what happened with mine (central MA). The old felt just disintegrated, but the plywood underneath was fine except where I had ice dam leaks. I went with synthetic this time mostly for the install - weather delays are a pain and it just seemed tougher. Haven’t seen a warranty actually denied over underlayment type, at least not from neighbors or my own experience. If you’ve got decent ventilation and keep up with insulation, I honestly think either works, but synthetic does feel like cheap insurance when the weather turns mid-project.

- Felt turning to dust after 15+ years seems pretty normal from what I've seen. Decking holding up is a good sign - means the main job got done.
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“synthetic does feel like cheap insurance when the weather turns mid-project.”

“synthetic just sits there and shrugs it off.”

That’s been my experience too - felt turns into confetti if a storm rolls in mid-job. I’ve seen more than one neighbor chasing tarps down the street. You nailed it about the slippery synthetic, though... nearly slid off a 10/12 once before coffee. Still, I’d pick it again for peace of mind.

I hear you on the synthetic being slick - especially on a steep pitch, it’s no joke. But honestly, I’d still take that over felt any day for durability. Around here (Midwest), storms are unpredictable and I’ve seen felt just disintegrate if it sits exposed for even a day or two. Synthetic’s not perfect, but it buys you time if weather turns. Only real downside is the price and that learning curve with footing... but for longevity, it’s hard to beat.

Synthetic’s not perfect, but it buys you time if weather turns. Only real downside is the price and that learning curve with footing... but for longevity, it’s hard to beat.

I get where you’re coming from about the slickness - on a 10/12 or steeper, synthetic can feel like walking on ice. I’ve had a couple guys nearly end up in the bushes before we got used to it. But honestly, after seeing what Midwest storms do to felt, I’m not going back. Had a job last spring where we got rained out halfway through - synthetic held up fine for three days until we could finish. If that had been 15# felt, it would’ve turned to mush and we’d be redoing half the underlayment.

The price stings a bit, yeah, but I figure it saves me headaches (and callbacks) down the line. Only tip I’d add: invest in some good shoes with sticky soles if you’re working on synthetic, especially when there’s dew or frost. It’s not perfect, but for unpredictable weather and longer exposure times, synthetic’s just less hassle overall.

I hear you on synthetic holding up better in storms, but I’ve seen felt outperform it in certain situations - especially on lower slopes or when you’re dealing with a lot of foot traffic during install. Synthetic can tear if you’re not careful with ladders or tools, and once it’s ripped, water finds its way in just as fast. Plus, some of the cheaper synthetics don’t breathe at all, so if there’s any moisture trapped underneath, you’re asking for rot down the line. I still use felt on smaller jobs or where we can get shingles on quick. Not saying synthetic’s bad, but it’s not always the slam dunk folks make it out to be.

Had a similar debate with myself last year when I redid my garage roof. Ended up going with felt because I was worried about all the ladders and tools moving around - didn’t want to risk a tear. It rained halfway through the project and the felt held up fine. I’ve heard the higher-end synthetics breathe better, but honestly, on a smaller job where you’re not leaving it exposed for long, felt still seems like the safer bet. Maybe I’m just old school, but it’s worked for me so far.