I hear you on the heat thing. Swapped to synthetic a few years back after a nasty leak, and yeah, the attic definitely feels warmer now. My cooling bill crept up a bit, but I chalked it up to the hotter summers... maybe not? I do miss how felt seemed to breathe better, even if it needed patching more often.
That’s interesting—did you notice if your attic ventilation changed at all when you switched to synthetic? I’ve seen a few cases where folks swapped out felt and suddenly the attic turned into a sauna, especially if the vents weren’t up to snuff. Sometimes it’s not just the underlayment, but how everything works together. Felt definitely breathes more, but yeah, patching gets old fast. Did you see any condensation or moisture issues since the switch, or just higher temps?
Sometimes it’s not just the underlayment, but how everything works together.
That’s been my experience too. When we switched to synthetic on a couple of our properties, I noticed the attic temps crept up a bit, but nothing wild—though we did have to add a ridge vent to one building that was borderline before. Haven’t seen any real condensation issues, but I do keep an eye out, especially after heavy rain. Curious if you had to tweak your ventilation setup at all, or did things stay pretty stable? It’s always a balancing act with these older roofs...
We had to mess with the soffit vents a bit after switching to synthetic—seemed like airflow just wasn’t quite right at first. I’m in a humid area, so I get nervous about trapped moisture. Did you notice any difference in shingle temp or lifespan? I’ve heard mixed things about how synthetics affect that, but haven’t seen much change myself.
I’ve been wondering about the same thing, honestly. I switched to synthetic underlayment last year when we replaced the roof (asphalt shingles, mid-Atlantic, pretty humid summers but not Florida-level). I read a bunch about how synthetics are supposed to “breathe” better, but then you see all these warnings about moisture getting trapped if your attic ventilation isn’t dialed in. I haven’t noticed any shingle curling or weird heat issues yet, but it’s only been through one summer.
Did you have to add more soffit or ridge vents after you switched? I’m still trying to figure out if my attic fan is helping or just moving hot air around. My neighbor swears his shingles are hotter since he went synthetic, but I’m not sure if that’s just because he’s got a darker color up there now.
I did notice the attic felt a bit stuffier on those really humid days, but it’s hard to tell if that’s the underlayment or just the weather. Did you check your attic humidity before and after? I’m thinking about getting one of those cheap sensors just to see if there’s a real difference.
Also, did your installer mention anything about warranty changes with synthetic? Mine said it was fine, but I’ve read some manufacturers get picky if you don’t follow their venting specs exactly. Just curious if you ran into any of that—seems like every roofer has a different take on what “proper ventilation” actually means.
