If underlayments could talk: which one would outlast the others?

You’re making smart choices - just keep an eye on those transitions and penetrations. That’s where most of the headaches start.

Couldn’t agree more about transitions. I learned the hard way - flashing around my chimney was fine, but the underlayment detail was sloppy and I ended up with a slow leak that took months to track down. For what it’s worth, I’ve found that layering ice and water shield a foot or two up from every penetration (not just valleys/eaves) is worth the extra cost, especially in freeze-thaw climates. Synthetics are great for breathability and longevity, but I still trust felt for certain spots, even if it’s a pain to haul up. Matching the material to the job is key, but I’d say don’t skimp on overlap or fasteners either... those shortcuts always come back to bite.

Transitions and penetrations are definitely where I see the most issues during inspections, especially around chimneys and skylights. Even when the flashing looks textbook, if the underlayment isn’t lapped right or gets punctured, water finds a way in - sometimes for years before anyone notices. Ice and water shield up from every penetration is a solid move, particularly in places with freeze-thaw cycles. I’ve seen too many “mystery leaks” that trace back to skipping that step.

I get the felt vs. synthetic debate. Synthetics have come a long way, but there are still spots where old-school felt just seems to seal better, especially under metal flashing or in areas that might see some foot traffic during install. It’s heavier and more awkward, but sometimes worth the hassle.

And yeah, fasteners and overlap - people cut corners there all the time thinking it’ll be fine, but it rarely is. The devil’s in the details with roofs... and water always finds the smallest mistake.

Had a similar issue last year - water sneaking in right by the chimney.

“Even when the flashing looks textbook, if the underlayment isn’t lapped right or gets punctured, water finds a way in - sometimes for years before anyone notices.”

I get the appeal of synthetic - lighter, easier to handle, and all that. But I’m still a bit skeptical about its long-term durability, especially in hot climates. The old felt on my place lasted decades with barely any fuss. Sometimes newer isn’t always better... anyone else notice synthetics getting brittle after a few years?

Sometimes newer isn’t always better... anyone else notice synthetics getting brittle after a few years?

That’s the thing - on paper, synthetics are supposed to outlast felt by a mile, but I’ve seen plenty get crispy and start cracking after just 7-8 years, especially on south-facing slopes. It’s not just the heat, either. UV exposure during install can really mess them up if the shingles don’t go on fast enough. Felt might be heavier and a pain to haul up a ladder, but I’ve torn off 30-year-old roofs where the old #30 was still holding together.

Curious if anyone’s had luck with those “high-temp” synthetics? Supposedly they’re made for hot climates, but I haven’t seen much real-world proof yet. Anyone actually pulled up a roof after a decade and checked what’s underneath?