When we bought our place, I thought picking a “good” underlayment was the main thing, but after poking around in the attic, it’s clear airflow is king. We had some insulation blocking soffits...
That “inside-out rot thing” really does catch folks off guard. I’ve seen more damage from blocked soffits than from cheap underlayment, honestly. Here’s how I usually check: 1) pop into the attic on a cold day, 2) look for frost or wet spots on nails, 3) make sure insulation isn’t stuffed right up to the eaves. If you spot any of that, it’s usually a ventilation problem, not just an underlayment issue. Fancy synthetics are nice, but if the attic can’t breathe, you’re just trapping problems inside.
Couldn’t agree more about ventilation being the real difference-maker. I’ve torn off roofs where the underlayment was barely holding together, but the attic was dry and healthy because the airflow was dialed in. On the other hand, I’ve seen “top shelf” synthetic underlayments paired with blocked soffits, and the sheathing was mush after a decade. Sometimes people get so focused on the latest product that they forget you can’t out-engineer poor ventilation. Makes me wonder if we overthink underlayments a bit, especially in average climates...
I get where you’re coming from—ventilation is huge, no question. But I wouldn’t write off underlayments as just an afterthought, even in average climates. I’ve seen plenty of storm damage where the only thing keeping water out for a few days (or weeks) was a solid synthetic underlayment. Felt would’ve been toast in those situations. Sure, if the attic’s bone dry and airflow’s perfect, you might not notice the difference for a while, but when you get a wind-driven rain or a shingle blows off, that’s when the underlayment earns its keep.
I do agree that people sometimes chase the latest “miracle” product and forget the basics, but I’d still rather have a decent synthetic underlayment as a backup. It’s not a cure-all, but it’s saved a lot of headaches after hail or a bad storm. Maybe we overthink it sometimes, but I’ve seen enough roofs where the underlayment was the last line of defense to say it matters more than folks think.
If we’re talking about which underlayment would “finish last” in a race—meaning, which one holds up the longest when things go sideways—I’d have to agree that synthetic usually outpaces felt by a mile. I’ve pulled up old roofs after storms and sometimes the only thing between the decking and a soaked attic was that synthetic sheet. Felt just doesn’t seem to handle standing water or wind-driven rain for long, especially if there’s any kind of delay before repairs.
But I do wonder if we sometimes overlook the basics, like you said. I’ve seen some folks throw down high-end synthetics but skip proper flashing or ventilation, and then blame the underlayment when there’s a problem. It’s all about the system working together, right? Still, if I had to bet on which one would “limp across the finish line,” it’d be #15 felt every time. Maybe in a dry climate it’s fine, but anywhere with real weather... not so much.
I’m curious if anyone’s actually seen those newer self-adhered membranes in action after a storm. Are they worth the extra cost, or just overkill for most jobs?
I’m curious if anyone’s actually seen those newer self-adhered membranes in action after a storm. Are they worth the extra cost, or just overkill for most jobs?
We had a section of flat roof with a self-adhered membrane take a direct hit from a hailstorm last year. No leaks, even though the shingles above were trashed. The upfront cost was higher, but it saved us on interior repairs and insurance headaches. For critical areas—valleys, eaves, low slopes—I’d say it’s money well spent. For a basic gable in a mild climate, maybe not necessary. It really comes down to risk tolerance and budget.