- Not sure I buy that it’s just the underlayment. I’ve got a 4/12 pitch (so, not super steep), and after last winter’s freeze, I noticed some damp spots in the attic too.
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“Sometimes it’s not just the underlayment, but airflow issues making things worse.”
That tracks. I crawled up there and found one vent half-blocked by old insulation. Cleared it out and things dried up faster after storms.
- Ice dams are a pain—had one form above my kitchen last January. Didn’t even realize until water started dripping down the wall. Ended up having to chip away at it from outside with a broom handle (not recommended, but desperate times...).
- My inspector said felt underlayment “breathes” more than synthetics, but honestly, both seem to hold moisture if there’s nowhere for it to go.
- If your roof survived a hurricane, that’s great—but I wouldn’t chalk it all up to luck. Maybe your vents are working better than you think? Or maybe you just haven’t had the right combo of cold + wet yet.
- For what it’s worth:
- Check soffit and ridge vents for blockages (mine had bird nests).
- Make sure insulation isn’t covering vents.
- If you’ve got a low slope, watch for pooling water or slow-drying frost.
- If you’re seeing moisture inside after storms or frosts, might be worth getting a pro to look at airflow before blaming the underlayment.
- Still not convinced synthetic vs felt is the main issue here... seems like airflow and pitch matter way more in my experience.
“Still not convinced synthetic vs felt is the main issue here... seems like airflow and pitch matter way more in my experience.”
I’m with you on that. I’ve managed a bunch of properties with all sorts of roof types, and honestly, the ones with poor ventilation always have more problems—regardless of underlayment. Had a place with perfect shingles and fancy synthetic, but blocked soffits led to moldy rafters anyway. Curious if anyone’s actually seen a big difference after switching underlayment, or is it mostly about keeping those vents clear?
Had a similar situation last year—swapped out old felt for synthetic on a low-slope roof, but honestly, the real improvement came after we fixed the attic ventilation. Before that, even the “better” underlayment didn’t stop condensation issues. I get why folks like synthetic for durability, but if airflow’s off, it just delays the inevitable. Maybe in extreme climates underlayment matters more, but around here, venting seems to make or break it.
You nailed it—ventilation really is the unsung hero. I’ve seen folks spend a fortune on fancy underlayments, but if the attic’s a sauna, you’re still chasing leaks and rot. Around here, proper airflow saves more roofs than any product swap ever did.
Isn’t it wild how folks will drop big bucks on “hurricane-proof” shingles, but then ignore the attic vents? I’ve seen more mold and warped decking from trapped heat than from actual wind damage. Did you use ridge vents or just soffits? Sometimes I wonder if those solar fans actually help or just suck up your money…