Had a similar experience with synthetic under metal, actually.
That’s exactly what happened on my shed roof—south-facing, lots of sun, and the synthetic just started cracking around the nails after maybe 4 years. Never had that with felt, even when it got a bit soggy in the summer. I get why folks like synthetic for the weight and coverage, but I’m not convinced it’s always the better long-term bet, especially down here where the humidity is relentless.“I’ve seen some of these newer synthetics get brittle or curl up after a few years under metal—especially if there’s a lot of sun exposure.”
- Had a similar issue with synthetic underlayment on a low-slope metal roof, southeast Texas.
- After about 5 years, the stuff got brittle and started tearing near the fasteners—especially on the sunniest side.
- Felt isn’t perfect, but I’ve noticed it tends to stay flexible longer, even when it gets damp.
- Synthetics are lighter and easier to roll out, but in hot, humid climates, I’m not sure they’re worth the trade-off.
- If I had to do it again, I’d probably stick with a heavier felt or look into some of the newer “breathable” options, though those are pricier.
That’s interesting—especially the part about the synthetic tearing up after just five years. I’m in central Louisiana, so not too far off climate-wise, and I’ve been going back and forth on this exact thing. Here’s how I broke it down for myself:
Step 1: Figure out what you’re up against. For me, it’s heat, humidity, and the occasional hurricane. I kept reading that synthetics are “tougher,” but then I saw stuff like this:
After about 5 years, the stuff got brittle and started tearing near the fasteners—especially on the sunniest side.
Step 2: Compare the install. Synthetics are definitely easier to handle solo (I’m not exactly a pro up there), but if it’s going to crack in the sun, that’s a problem.
Step 3: Think about longevity. I’ve seen old felt underlayment still hanging on after 10+ years, even if it’s a bit soggy. Not perfect, but at least it doesn’t just disintegrate.
Step 4: Budget check. The “breathable” options look cool, but my wallet says nope for now.
I’m leaning toward a heavier felt too, maybe with some extra fasteners on the windward side. If it gets me through a decade, I’ll call it a win.
I kept reading that synthetics are “tougher,” but then I saw stuff like this:Step 2: Compare the install.
I get where you’re coming from, but I’ve actually had the opposite experience with synthetics. My neighbor used a mid-grade synthetic on his shed, and after two hurricanes and a ton of sun, it’s still holding up—no brittleness yet. Maybe it depends on the brand or thickness? Felt always seemed to get mushy for me after a few years, especially when we had those long stretches of rain. Just my two cents...
Maybe it depends on the brand or thickness? Felt always seemed to get mushy for me after a few years, especially when we had those long stretches of rain.
That’s interesting—I’ve noticed the same thing with felt getting soggy over time, especially in wet climates. I wonder if some of the issues folks see with synthetics are from using thinner rolls or maybe not fastening them right? I’ve seen some brands that are paper-thin and others that feel almost tarp-like. It’s tough to compare unless you know exactly what was installed. Either way, your neighbor’s shed sounds like a good test case.
