- Did my own roof with felt a few years back (asphalt shingles, Midwest, lots of wind). Looked fine at first, but after two winters, I started seeing some curling and a couple leaks around the vents. Not a total disaster, but definitely more patching than I wanted.
- Neighbor went with synthetic underlayment last year. He’s had zero issues so far, even after a couple nasty storms. He swears by it, but he also paid about 2x what I did for materials.
- Synthetic is lighter and easier to handle, which was a big plus when I helped him out. Didn’t tear as easy as felt when we were moving around up there.
- Downside: If you’re on a tight budget, felt is way cheaper. But if you’re planning to stay in the house a while, synthetic might save you headaches down the road.
- Marketing hype? Maybe a little, but from what I’ve seen, synthetic does seem to hold up better in rough weather. If you’re somewhere mild, felt might be “good enough,” but I wouldn’t risk it again where I live.
- Just my two cents... If I ever re-roof, I’m probably going synthetic, even if it means eating ramen for a month.
Interesting to hear about the felt curling after just a couple winters. I’ve been reading up on this and some folks say vent leaks are more about flashing than underlayment, but maybe the felt just doesn’t hold up as well in wind. Did you notice if the leaks were right at the seams or more random? Also curious if anyone’s tried mixing both—like synthetic in trouble spots and felt elsewhere—or is that just asking for trouble?
Mixing underlayments is something I’ve wondered about too, especially since my garage roof has a couple spots where the wind just rips through every winter. I haven’t tried it, but I’m curious if anyone’s had issues with moisture getting trapped between layers, or if it messes with how the shingles lay. Also, for those who’ve had vent leaks—did you notice any difference depending on the roof pitch or attic ventilation? I keep reading conflicting stuff about that.
Mixing underlayments can get tricky, especially if you’re layering synthetic over felt. I’ve seen moisture get trapped between layers when there’s not enough ventilation, and that can lead to rot or mold down the line. As for shingle lay, sometimes double underlayment makes things a bit uneven—depends on the thickness. On vent leaks, steeper pitches usually shed water better, but poor attic airflow can still cause condensation issues regardless of slope. It’s all about balance—good underlayment, solid ventilation, and making sure everything’s sealed up tight where the wind hits hardest.
Mixing underlayments always gets people talking. I’m with you—layering synthetic over felt can be a gamble, especially in humid spots. Have you looked into the recycled rubber or plant-based options? They’re pricier but I’ve found they breathe better and don’t trap moisture like the synthetics sometimes do. Curious if anyone’s seen how those hold up long-term, especially with weird weather swings. And yeah, if your attic can’t vent right, no amount of fancy underlayment will save you from mold.
