so anyway this has been bugging me for a few days and i figured id just post it. did a commercial flat roof inspection last week, big warehouse, maybe 80,000 square feet. client wanted thermal to find moisture intrusion and i flew it late afternoon thinking the surface would still be warm enough from the day. used the M30T and flew a grid at about 40 feet AGL.

the imagery came back and honestly it was kind of a mess. got a ton of false positives i think ? areas that looked hot that the roofer said were totally fine when he went up there. im wondering if the timing was off or if 40 feet is too low for thermal to read properly on a flat membrane roof. ive done residential pitched roofs before and those came out great but this is my first big flat commercial job. any thermal guys here who do this regularly know what im probably screwing up

timing is almost certainly your issue. flat roofs are tricky because the whole surface heats up pretty uniformly during the day and then it starts releasing heat in kind of unpredictable ways depending on whats underneath. the sweet spot for moisture work is usually 1 to 3 hours after sunset when the dry areas have cooled down but the wet spots are still holding heat. late afternoon you're basically fighting the ambient surface temperature the whole time and everything looks warm.

altitude wise 40 feet is fine for a roof that size, i usually go a bit higher on big flat jobs just to get better coverage per pass and reduce the total flight time, maybe 60-80 feet. but thats not gonna cause false positives like you described, thats definitely the timing thing.

yeah what he said about timing. also worth checking if there were any HVAC units or vents on that roof because those will absolutely throw off your whole thermal read if theyre running. had a job once where a rooftop unit was cycling on and off and it looked like half the roof was saturated when it was fine. roofer thought i was an idiot until we figured it out lol