Why some roof coatings actually make things worse

Did you check for ventilation under your deck before sealing it? Sometimes airflow makes all the difference.

That’s actually something I learned the hard way. Last summer, I sealed the deck without thinking about airflow underneath - figured a good coat would keep out the rain. Ended up with musty smells and some weird warping a few months later. Turns out, moisture just sat there since there was nowhere for it to go. Had to pull up a few boards and add vents after the fact. Live and learn, I guess. Sometimes those “quick fixes” just make more work down the line.

I get where you’re coming from, but I’m not totally convinced that adding vents is always the answer. In my case, I actually had too much airflow under the deck and it dried things out so much that the boards started to split. I guess it really depends on your climate and how much moisture you’re dealing with. Sometimes sealing without thinking about the bigger picture just traps problems, but too much ventilation can cause its own set of headaches. There’s definitely a balance to strike.

That’s a good point. I’m in a pretty humid area, so I was worried about mold and went heavy on the vents - ended up with chilly floors and cracks in a couple of boards. It’s definitely not one-size-fits-all. Sometimes the “fix” just shifts the problem around.

That sounds familiar - humidity really does throw a wrench into the usual advice, doesn’t it? I’m in the southeast, and when I first moved here, I was all about maximizing airflow to keep things dry. But after a couple of years, I realized too much venting was pulling in damp air during those sticky summer nights, which didn’t help at all. My neighbor had a similar issue with his roof coating: he went with a reflective sealant thinking it’d keep things cooler, but it actually trapped moisture underneath and warped some of his decking.

It’s wild how something that works perfectly in one climate can backfire just a few states over. I’ve started paying more attention to the whole system - roof color, insulation, even landscaping around the house. There’s no magic bullet, just a lot of little tweaks. Sometimes I wonder if we’re all just chasing balance and hoping the next fix won’t create its own headache...

It’s wild how something that works perfectly in one climate can backfire just a few states over.

That’s the part that always trips people up. I see a lot of folks who move from drier regions and try to apply the same “rules” here in the southeast, only to run into moisture headaches they never expected. Roof coatings are a classic example - reflective or elastomeric coatings can be great for heat reduction, but if the roof deck or attic isn’t vented *just right*, you end up with condensation trapped between layers. That moisture has nowhere to go, and over time, it’ll rot decking or even cause mold issues.

I’ve inspected homes where owners thought they were doing everything by the book - good insulation, plenty of soffit and ridge vents, even upgraded attic fans. But when humidity spikes at night, all that airflow just brings in more damp air, especially if there’s no vapor barrier in place. Sometimes less is actually more when it comes to venting around here.

One thing I’d add: landscaping can play a bigger role than people realize. If you’ve got dense shrubs or trees right up against the house, it can keep things shady but also trap moisture near the foundation and walls. I’ve seen crawlspaces with persistent dampness just because of poor airflow outside.

There’s definitely no one-size-fits-all solution. Even roof color can make a difference - lighter roofs reflect heat but sometimes don’t dry out as fast after rain, which can be a problem if you’re already fighting humidity. I usually tell people to look at their whole setup: attic insulation type and thickness, vapor barriers (or lack thereof), roof slope, even gutter placement.

It’s a balancing act for sure. Every tweak seems to have some tradeoff, and what works for your neighbor might not work for you - even if you’re just down the street. The best advice I can give is to pay attention to how your house “behaves” through each season and adjust slowly rather than making big changes all at once. Sometimes chasing that perfect fix just leads to new surprises...

- Not sure I totally agree about venting being the main culprit. I’ve lived in the southeast my whole life, and honestly, most of the moisture problems I’ve seen came down to poor installation or just old, leaky roofs - not so much the coatings themselves.
- Had a neighbor put on a reflective coating last summer (asphalt shingle roof, medium pitch). He didn’t change anything else - no extra vents, no new insulation. No issues so far, and his attic is noticeably cooler. Maybe he just got lucky, but it’s not always a disaster.
- I do think you’re right about landscaping, though. I had to rip out a bunch of overgrown azaleas that were basically hugging my crawlspace. Made a huge difference in how dry it stays under there.
- For me, the biggest headache was gutters. Once I added bigger downspouts and made sure water moved away from the house, a lot of my “humidity” problems disappeared.
- I guess my point is, sometimes it’s not the coating or the venting - it’s just basic maintenance stuff getting overlooked. Not saying coatings can’t cause issues, but I wouldn’t blame them for everything.

I guess my point is, sometimes it’s not the coating or the venting - it’s just basic maintenance stuff getting overlooked.

That makes sense. I’ve noticed a lot of folks jump straight to blaming the coating when there’s a leak or moisture, but sometimes it’s just clogged gutters or missing flashing. Out of curiosity, has anyone actually seen a reflective coating cause condensation issues in an attic? Or is that more of a theoretical risk than something that happens in real life? I keep hearing about it, but haven’t run into it myself.

I’ve actually wondered about that too, since I live in a pretty humid area (Gulf Coast). Had a reflective coating put on my old ranch house roof a few years back - mainly to cut down on attic heat. Never saw any new condensation issues, but I did notice the attic stayed cooler, which was nice. From what my roofer said, condensation’s more about poor ventilation or insulation gaps than the coating itself. Maybe in a super airtight house with no venting it could be a problem, but I haven’t seen it firsthand. Usually it’s just blocked soffit vents or something simple like that.

That lines up with what I’ve seen managing properties along the coast - ventilation is usually the real culprit when it comes to attic moisture. Reflective coatings can help with heat, but if the attic can’t breathe, you’re still going to run into problems, coating or not. I had a place out in Mobile where we kept getting these weird water stains on the ceiling. Turned out the soffit vents were clogged with old insulation and a couple bird nests (go figure). Once we cleared those out and added a ridge vent, no more issues.

I get why people worry about coatings trapping moisture, but in practice, I’ve found it’s pretty rare for the coating itself to cause trouble unless something else is already wrong. The only time I’ve seen a coating make things worse was on a flat roof with zero ventilation and a ton of shade - basically a recipe for condensation no matter what you put on top.

Sounds like you did everything right. If your attic’s staying cooler and you’re not seeing new moisture, that’s a win in my book. Sometimes folks overthink these upgrades, but most of the time it just comes down to making sure air can move where it needs to. If anything, I wish more people would check their vents before dropping money on big fixes.

Anyway, glad to hear your experience was positive. Always nice when something actually works as advertised... doesn’t happen as often as we’d like!

I’ve run into this a bunch, especially on older homes where folks try to “fix” a hot attic by slapping on a reflective coating and calling it a day. One place I inspected last year had a nearly new white elastomeric coating, but the homeowner was still complaining about musty smells and even some mold spots on the rafters. Turned out, the attic vents were painted shut (probably from a previous exterior paint job), and there was zero airflow up there. The coating did help with heat, but all that trapped moisture had nowhere to go.

Here’s how I usually break it down for clients:

1. Start with ventilation. Before you even think about coatings, check every vent - soffit, ridge, gable, whatever you’ve got. Make sure they’re open and not blocked by insulation, debris, or, yeah, birds. I’ve seen everything from squirrel nests to wasp hives clogging things up.

2. Look at insulation next. Sometimes people pile it right over the soffit vents without realizing it’s blocking airflow. A quick peek with a flashlight can save a lot of headaches.

3. Only after those two are sorted do I suggest considering coatings. They’re great for reflecting heat, especially in places like the Gulf Coast or Southwest, but they’re not magic. If the attic can’t breathe, you’re just locking in problems.

I do think coatings get a bad rap sometimes - like you said, they rarely cause issues on their own unless something else is off. But I’ve also seen cases where folks blame the coating when really it’s a ventilation or insulation problem that’s been there for years.

One thing I’m still not totally sold on is using heavy-duty waterproof coatings on low-slope roofs in humid climates. I get why people want the extra protection, but if there’s no way for vapor to escape, you’re just asking for condensation and rot. Maybe someone’s had better luck with those than I have.

Anyway, it’s always satisfying when a simple fix like clearing vents solves what looked like a big problem. Makes me wonder how many expensive “repairs” could be avoided if people just checked airflow first...

Funny you mention the heavy-duty waterproof coatings on low-slope roofs - I've always been a bit skeptical about those too, especially around here where humidity is basically a year-round sport. I get why folks want to slap on something that promises “no more leaks ever,” but does anyone really believe that’s the end of the story? Every time I see one of those roofs, I start poking around for signs of trapped moisture. Nine times out of ten, there’s at least a little bit of staining or that telltale musty smell hiding somewhere.

I’ve had a couple clients who went all-in on those coatings after a bad storm season, thinking it would solve their problems for good. Fast forward a year and they’re calling me back because their ceiling is sweating in July and they can’t figure out why. Turns out, the roof’s basically wearing a raincoat with no way to dry off underneath. It makes me wonder if we’re just trading one problem (leaks) for another (rot and mold).

One thing I’m still trying to wrap my head around: why do people skip right over the ventilation step? Is it just not as flashy as putting on a shiny new coating? Or maybe it’s because you can’t see airflow, so it doesn’t feel like “real” work got done? I’ve lost count of how many times I’ve found soffit vents stuffed with insulation or painted shut like you mentioned. Sometimes I feel like half my job is just pointing at blocked vents and asking, “Hey, what do you think happens when air can’t get through here?”

And insulation - don’t even get me started. It’s wild how often people pile it up thinking more is always better, not realizing they’re suffocating their own attic space. Maybe we need an attic version of Goldilocks: not too much, not too little... just enough to keep things breathing.

Anyway, totally agree that coatings aren’t evil by themselves. But if the basics aren’t right first, you might as well be putting lipstick on a pig. Curious if anyone’s actually had long-term luck with those thick waterproof coatings in muggy areas without running into condensation issues... or is that just wishful thinking?

- Ran into this exact thing last summer. We did a coating job on a flat roof for a neighbor - looked great at first, but by August, the inside was starting to smell funky.
- Pulled back some ceiling tiles and, sure enough, there was moisture trapped between the coating and the old roof. No leaks, but definitely not dry either.
- The owner had blocked off a bunch of vents “to keep bugs out,” which just made it worse.
- I get why people love those coatings - easy fix, looks clean, and you can brag about it to your friends. But if the roof can’t breathe, it’s just asking for trouble in humid places like ours.
- Ventilation seems boring compared to shiny new stuff, but honestly, it’s what keeps everything from turning into a science experiment up there.
- I’ve seen a couple of jobs where the coating held up okay, but only when the attic was vented right and insulation wasn’t piled up everywhere.
- Not saying coatings are bad, just that they’re not magic. If you skip the basics, you’ll probably end up with a different headache down the road.

I’ve always wondered - do folks realize how much those blocked vents can mess things up? I get wanting to keep bugs out, but trapping moisture is way worse. Ever tried those mesh vent covers? They let air flow but keep critters out. Curious if anyone’s had luck with those.

Ever tried those mesh vent covers? They let air flow but keep critters out.

Yeah, I’ve seen those mesh covers work pretty well, especially on older homes where bugs and birds love to sneak in. Just gotta make sure the mesh isn’t too fine or it’ll clog up fast with dust and stuff - then you’re back to square one with blocked vents. Moisture buildup is no joke under a roof... I’ve had to crawl into some gnarly attics because someone thought stuffing vents was a good idea. Mesh seems like a decent middle ground if you keep an eye on it.

- Mesh covers are a solid idea, but yeah, if you go too fine it’s basically a dust trap.
- I’ve seen folks use screen door mesh - seems to balance airflow and critter control pretty well.
- Agree about moisture - blocked vents are a nightmare. Had mold in my attic once because insulation was jammed right up against the soffit vents.
- Curious if anyone’s tried those “breathable” roof coatings? I hear some can actually trap moisture if your venting isn’t dialed in... seems like it could make things worse instead of better.

Curious if anyone’s tried those “breathable” roof coatings? I hear some can actually trap moisture if your venting isn’t dialed in...

That’s spot on - seen a few cases where folks thought a “breathable” coating would fix leaks, but it actually kept dampness locked in the sheathing. Anyone ever deal with condensation issues after adding a coating, or is that mostly a cold climate thing?

Had a job last year where the homeowner put down a “breathable” elastomeric coating over an old torch-down roof, thinking it’d help with some minor leaks. Thing is, their attic venting was pretty minimal - just a couple of old gable vents and no soffits. After the first winter, they started seeing mold spots on the sheathing and some weird musty smells. Turns out, the coating slowed down the drying even more, so whatever moisture got in just sat there. Ended up having to pull a bunch of insulation and replace some decking.

I’ve noticed it’s not just a cold climate thing either. I’m in the mid-Atlantic, and we get humid summers. If the roof can’t “breathe” both ways - out and in - you’re asking for trouble. Those coatings can be great if everything else is dialed in, but if you’ve got poor venting or any hidden leaks, they’ll just lock in the problem.

Curious if anyone’s tried these coatings on metal roofs? I’ve only seen issues on flat or low-slope with older built-up or mod bit roofs. Wondering if the same moisture trapping happens with metal, or if it’s less of a concern since metal doesn’t absorb water like wood or asphalt. Also, has anyone had luck improving attic ventilation after the fact to fix these issues, or is it usually too late once the coating’s on?

- I get where you’re coming from, but I’ve actually seen elastomeric coatings help in some cases, even with less-than-ideal venting. Had a 60s ranch with a low-slope mod bit roof - owner put on a “breathable” white coating mainly for heat reflection. Their attic venting was just two gables, no soffits, but they didn’t get mold or musty smells after two years. Maybe luck, maybe the leaks were truly sealed up first?
- On metal roofs, I’ve managed a couple properties where folks used elastomeric coatings to cut down on summer heat. Haven’t seen the same moisture issues as with built-up or torch-down. Metal doesn’t soak up water, and if there’s a vapor barrier under the metal, it seems to help. Still, if there’s condensation from inside (like kitchens or bathrooms venting into the attic), you can get drips and rust over time.
- Improving attic ventilation after the fact isn’t always too late. We retrofitted a few buildings with ridge vents and solar fans after coatings went on - definitely helped with humidity and smell. Not a magic fix, but better than nothing.
- One thing I’d push back on: sometimes the “breathable” label is more marketing than reality. Some coatings are way less permeable than advertised, especially after a few years of UV.
- If you’re dealing with older roofs, I’d say focus on sealing leaks and boosting venting before worrying about coatings. But if you’re stuck with what you’ve got, adding powered vents or even just cracking an attic hatch in dry weather can make a difference.
- Every roof’s different... sometimes you get lucky, sometimes you’re pulling out insulation and cursing last year’s decisions.

Those “breathable” coatings always make me raise an eyebrow - seen too many that turn into plastic wrap after a couple summers. I’ve patched up a few roofs where moisture got trapped underneath and the decking started to rot. If you’re lucky and the leaks are sealed, you might dodge the bullet for a while, but I wouldn’t count on it long term. Metal roofs definitely handle coatings better since they don’t absorb water, but if you’ve got bad venting, even metal can sweat like crazy. Retrofitting vents is usually worth it, even if it’s just solar fans or more gable vents. Every roof’s its own beast… sometimes you win, sometimes you’re tearing out soggy insulation wondering what went wrong.

That’s been my worry with coatings too - sometimes they sound great on paper, but in real life, stuff just doesn’t breathe the way you hope. I tried one of those “breathable” elastomeric coatings on my shed roof a few years back. Looked fine at first, but by the second summer, it felt like I’d shrink-wrapped the whole thing. Ended up with condensation pooling under the decking, and I had to pull up a section to dry it out.

I totally agree about venting. When I redid my main roof (asphalt shingles, midwest climate), I added two extra gable vents and a solar fan. It wasn’t cheap, but the attic stays way drier now. If anyone’s thinking about coatings, I’d say step one is making sure your ventilation is up to snuff - otherwise you’re just trapping problems inside.

Every roof really does have its own quirks. Sometimes you do everything right and still end up patching things you didn’t expect. But hey, at least we learn something new each time, right?