I get what you mean—synthetic underlayment’s supposed to be the wonder material, but I’ve seen it fail too, especially when nails aren’t sealed right. Did you use any extra tape on the seams, or just overlap and hope for the best? Sometimes I feel like the old tar paper was more forgiving when folks got a little sloppy...
Sometimes I feel like the old tar paper was more forgiving when folks got a little sloppy...
Funny you mention that—my uncle swears by tar paper for exactly that reason. I’ve mostly worked with synthetic, and yeah, it’s lighter and way easier to roll out, but if you miss a spot or don’t nail it right, water finds its way in. We did use seam tape on a couple jobs, but honestly, it felt like overkill unless the roof pitch was super low. Have you noticed any difference in how it holds up during heavy storms?
We did use seam tape on a couple jobs, but honestly, it felt like overkill unless the roof pitch was super low.
I’ve wondered about that too—on my last project, I skipped the seam tape since the pitch was decent and figured gravity would do most of the work. But then we had a sideways rain and I noticed a bit of seepage near a valley. Maybe overkill isn’t always a bad thing? For those using synthetic, do you double up at valleys or just rely on overlap? Curious if anyone’s seen long-term issues with that approach.
I had a similar situation last fall—pitched roof, used synthetic, just overlapped at the valleys. Looked fine until we got a heavy wind-driven rain and I found a damp spot in the attic. Ended up going back and taping those seams. It’s a pain, but I’d rather do it once than chase leaks later. Guess it depends how much weather your area throws at you...
Overlapping at valleys without sealing is a pretty common shortcut, but honestly, I’m not convinced taping is always the answer either. Synthetic underlayments are supposed to shed water, but in my experience, if you’re getting wind-driven rain up the valley, it’s usually a flashing detail issue or maybe the overlap just wasn’t wide enough. I’ve seen plenty of jobs hold up fine with just a solid 12" overlap and no tape, especially if the main roof pitch is steep. Taping can help, sure, but sometimes it just traps moisture underneath if there’s any condensation or minor leak elsewhere. Just my two cents... every roof seems to have its own quirks.
