I hear you on the rain delays—synthetic definitely holds up better if you need to leave it exposed. But honestly, I’ve seen felt do fine for a few weeks too, as long as it’s not getting hammered by sun or wind. One thing about synthetics:
—that’s always bugged me. Some of my guys actually prefer felt just for the traction, especially on steeper pitches. I guess it’s a tradeoff between grip and water resistance. For warranty, yeah, it’s a maze... sometimes the shingle manufacturer and underlayment brand point fingers at each other if there’s an issue down the line.Noticed it was a bit slick when I walked on it
That slickness on synthetic is no joke—nearly took a ride off a 7/12 last summer. I get why folks stick with felt for the grip, especially if you’re up there in the heat. But yeah, warranties are a headache... half the time it feels like nobody wants to own the problem.
I hear you on the slip-n-slide factor with synthetic, but honestly, I’ll take that over soggy felt any day. Had a section of felt basically melt into mush after a week of summer storms—talk about a mess. Synthetic’s been way tougher for me, even if it’s like walking on ice sometimes. Warranties are a pain either way... but at least I’m not patching leaks every spring now.
I’ve definitely done the “synthetic shuffle” a few times—nearly went skating right off a 6/12 last summer. But yeah, I’d rather risk a bruised ego than deal with felt turning into oatmeal after a week of rain. Had a buddy who tried to patch a felt section after it got soaked, and it just tore apart like wet tissue. He was not thrilled.
One thing I’m still not sure about is how synthetic holds up under shingles that get real hot. I’ve heard some folks say it can get brittle or even fuse to the shingles in crazy heat, but I haven’t seen it myself yet. Anyone actually run into that? Around here (Midwest), we get those 90+ degree days and the attic feels like an oven, so I’m half expecting to peel back a shingle one day and find the underlayment stuck to it like cheese on pizza.
Also, does anyone bother with double-layer felt anymore? My uncle swears by it for old-school jobs, but every crew I’ve worked with lately just rolls out synthetic and calls it good. Maybe it’s just easier to handle, or maybe everyone’s tired of hauling those heavy felt rolls up the ladder.
Curious if anyone’s had synthetic last through more than one reroof? Or does it always get trashed when you pull the old shingles? I haven’t been around long enough to see one survive a second round...
I’ve seen a lot of roofs in the Midwest where synthetic underlayment’s been used, and honestly, I haven’t run into one that fused to the shingles yet—even on those scorcher days where you can fry an egg on the driveway. Most of the quality synthetics are engineered to handle high temps, at least for the lifespan of typical asphalt shingles. That said, I have peeled back some old shingles and found the synthetic a little “imprinted” from the shingle granules, but nothing like it melting or sticking like cheese. Maybe with some of the cheaper brands or if someone leaves it exposed for weeks in direct sun, you might get more issues.
Double-layer felt is pretty rare now unless it’s a historic home or someone’s really set in their ways. I get why your uncle likes it—there’s something about that extra thickness that feels reassuring. But honestly, most folks just don’t want to deal with the weight and hassle when synthetics are lighter and faster to install. Plus, synthetics don’t turn into mush after a thunderstorm rolls through before you get shingles down.
As for re-roofing over synthetic—almost every time I’ve seen a tear-off, the underlayment comes up with the shingles or gets shredded in the process. It’s not really designed to survive two rounds; even if it looks okay at first glance, all those nails and staples leave holes everywhere. I wouldn’t trust it as a secondary barrier after a reroof.
One thing I will say: if you’re dealing with steep pitches or working solo, synthetics can be slicker than snot on a doorknob until you get some granules down. Seen more than one guy nearly take a ride off the edge because he forgot his shoes had no grip left.
If you’re worried about heat and longevity, just stick with one of the better-known synthetic brands and avoid leaving it exposed longer than necessary. For most Midwest jobs, that combo seems to hold up fine—at least until it’s time for new shingles again.
