Synthetic’s great for durability, but if water gets underneath, it doesn’t always dry out like felt does.
That’s been my experience too. Had a job last year where a small flashing leak went unnoticed for a bit—synthetic underlayment kept the deck from rotting, but man, that moisture just sat there. With felt, I’ve seen it dry out quicker, but it tears up so easy if you’re not careful. Honestly, both have their headaches... install makes all the difference.
I get where you’re coming from—synthetic definitely wins on tear resistance, but I’ve always had a hard time trusting it when it comes to breathability. Maybe it’s just habit, but I’ve seen way too many decks stay damp under synthetic, especially in our wet climate. Felt’s not perfect either, but at least it seems to let things air out a bit if water sneaks in.
Honestly, though, I think the bigger issue is how these materials fit into the bigger picture. If you’re using “green” roofing systems (like living roofs or even solar shingles), neither felt nor synthetic is ideal—there are better options that actually help manage moisture and heat instead of just acting as a barrier.
It’s wild how much depends on install, too. One bad staple or missed overlap and you’re dealing with rot no matter what you picked. I wish there were more good eco-friendly underlayments out there… most of what’s marketed as “green” still feels like a compromise.
I hear you on the breathability thing. In my experience, synthetic does hold up longer—less tearing when guys are walking on it, and it seems to handle UV better if the roof gets delayed. But I’ve noticed if there’s any moisture trapped underneath, it’ll just sit there way longer than with felt. Around here (Pacific Northwest), that’s a big deal. For “green” roofs, we started using a self-healing membrane designed for living roofs. It’s pricier, but honestly, it’s the only thing that’s kept rot at bay in our wetter months. Still wish there was a truly eco-friendly option that didn’t feel like a trade-off...
Yeah, the moisture hang-up with synthetics is a real headache, especially out here where it rains sideways half the year. I’ve seen plywood turn to mush under “waterproof” synthetics after just a couple months of trapped condensation. Felt breathes better, but man, it tears if you look at it wrong. The self-healing membranes are cool tech, but my wallet cries every time I order a roll... Still waiting for someone to invent a magic underlayment that’s tough, breathable, and doesn’t cost an arm and a leg.
Still waiting for someone to invent a magic underlayment that’s tough, breathable, and doesn’t cost an arm and a leg.
I feel this. I went with synthetic underlayment last fall because the installer swore by it, but honestly, I’m not convinced it was the right move for our climate (coastal Maine, constant damp). The stuff held up fine mechanically, but I noticed some weird condensation spots in the attic—never had that with felt. Felt might rip easier, but at least it lets the house breathe. If I could do it over again, I’d probably just double up on heavy felt and deal with the occasional tear. The “waterproof” claims on synthetics don’t mean much if your decking’s rotting underneath.