I've actually found humidity less of an issue than temperature swings. Silicone can handle moisture pretty well if the surface is clean, but big temp changes overnight seem to mess with adhesion more. Early morning might feel cooler, but surfaces can still have condensation...just something to consider.
Good point about the temperature swings. I've noticed similar issues when installing vents or flashing on my roof. Silicone can be pretty reliable, but it really depends on the surface prep and timing. Last summer, I made the mistake of sealing around a vent late in the afternoon—surface was warm, silicone went on smooth, everything looked perfect. Next morning though, after a cool night, I noticed some spots had lifted slightly at the edges. Pretty frustrating.
After that experience, I started paying more attention to timing and prep rather than just humidity or temperature alone. Now I usually aim for mid-morning installs—after any overnight condensation has dried off but before the roof gets too hot from direct sun. Also found that wiping down surfaces with rubbing alcohol helps silicone adhere better by removing any residual moisture or oils.
Another thing worth mentioning is silicone type. Not all silicones are created equal—some are specifically formulated for roofing or outdoor use and handle temperature fluctuations better than general-purpose stuff. I've had good luck with roofing-specific silicones labeled as "high-temp" or "weatherproof." They seem to stay flexible longer and resist lifting better through seasonal changes.
Anyway, you're definitely right about condensation being sneaky—even if the surface feels dry to touch, there might still be moisture trapped in tiny imperfections or seams. Waiting until surfaces warm up slightly (but not hot enough to cause rapid curing) seems to help avoid adhesion issues down the road.
Hope your attic fan install goes smoother from here out...these little details can make a big difference in longevity.
"Also found that wiping down surfaces with rubbing alcohol helps silicone adhere better by removing any residual moisture or oils."
Good tip about the rubbing alcohol—I hadn't considered leftover oils being an issue. I've been using acetone myself, but might give alcohol a try next time. Curious though, has anyone tried using butyl tape instead of silicone for sealing around vents? I've heard mixed reviews about its longevity compared to silicone, especially with temp fluctuations...
I've used butyl tape a couple times, and honestly, my experience was mixed. Installed it around some skylights in a rental property a few years back, thinking it'd hold up better to temperature swings. At first, it seemed great—easy to apply, sealed nicely—but after a couple hot summers and cold winters, it started cracking and lifting at the edges. Ended up switching back to silicone. Maybe others have had better luck, but silicone's been more reliable for me in the long run...
Had similar issues myself. A few quick thoughts based on what I've seen:
- Butyl tape works well initially, but long-term exposure to sun and weather seems to degrade it faster than you'd expect.
- Silicone, especially UV-rated, has held up better for me too—especially around roof penetrations like attic fans or vents.
- One trick I've learned: surface prep is key. Even a little leftover dirt or moisture can shorten lifespan dramatically.
- Funny enough, I used some butyl tape on a camper roof vent a while back, thinking it'd be bulletproof. Same story—cracked and peeled after a year or two. Switched to silicone and haven't looked back.
Guess it's one of those things that sounds great in theory, but real-world conditions tell a different story...
