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

- I’ve seen the same thing with felt - if it’s put down right, it can last way longer than people expect.
- Still kinda skeptical about felt vs. synthetic in spots where ice dams or standing water happen. Once moisture sneaks under, like you said, it’s game over.
- Anyone ever had issues with synthetic getting brittle after a few years in crazy heat? I hear mixed things but haven’t seen it myself yet...
- Curious if anyone’s compared how either holds up under metal roofs vs. shingles. Seems like the extra heat from metal would make a difference?

Curious if anyone’s compared how either holds up under metal roofs vs. shingles. Seems like the extra heat from metal would make a difference?

I’m wondering the same thing, honestly. We just bought a place with a metal roof and I keep picturing the attic turning into a giant toaster every summer. Is synthetic really up for that kind of heat, or does it just start crumbling like old crackers after a few years? I’ve heard felt can get weird and wavy if it gets wet, but synthetic seems like it could get brittle. Anyone ever peeked under a metal roof after a few years to see what’s actually happening?

- I’ve had both felt and synthetic under metal (in Texas, so it gets brutal).
- Synthetic held up better for me - no weird smells or crumbling after 6 years.
- Felt under an old shed roof got wavy and stuck to the metal in spots, especially where there was a leak.
- Metal definitely cooks the attic more than shingles, but the synthetic didn’t seem brittle - just dusty.
- Only thing: synthetic can get slippery if you’re up there working.
- Price-wise, synthetic was a little more upfront but didn’t need replacing as fast.
- Haven’t seen any cracking or major issues yet, but I do wonder how it’ll look after 15+ years...

I get the hype around synthetic, but I’m still not totally sold it’s the clear winner long-term.

“Haven’t seen any cracking or major issues yet, but I do wonder how it’ll look after 15+ years...”

That’s my hang-up too. My uncle’s place had synthetic under metal, and after about 12 years, it started to curl up at the edges where the fasteners were. Maybe it was a cheaper brand, but still - felt might be old school, but at least you know what to expect as it ages. Synthetic seems like a bit of a gamble past that first decade, especially in Texas heat. Anyone else notice it gets almost brittle if it’s exposed for too long before the panels go on?

Yeah, I’ve seen that brittleness too, especially if the synthetic sits out in the sun for a week or two. It’s like it just bakes. Felt isn’t perfect, but at least it doesn’t turn into a potato chip when you’re not looking.