To answer your question specifically, trapped moisture within a roof can be an issue at certain times on certain roofs. Here’s the scenario and how it plays out. When a flat roof system, whether it’s a BUR, TPO, PVC or EPDM, starts leaking it gets into the insulation where damage occurs and rot begins. Left alone and trapped, it gets worse.
We recommend an infrared scan on these types of roofs to check for trapped moisture within the roofing system, which provides tremendous insights that can save you money in the long run. A moisture scan will determine where the trapped moisture is in these types of roofs, if in fact it does exist. Remedial action required is to cut out the wet areas and re-ply the affected area prior to coating the roof. Roof vents typically don’t vent a large enough area to be effective in these scenarios and they don’t correct the “cancer” below.
Can you coat a roof with trapped moisture? Sure you can. But it will most certainly require maintenance moving forward and usually sooner as opposed to later. Once the underlying substrate is wet, the moisture that is trapped in the insulation will vaporize. Vapor always rises, and it will try to escape from the bottom up. As it tries to get out of the roof, it finds any crack and crevice it can to try and get out, but after a roof is coated, those cracks and crevices go away. If it can’t get out, it cooks. This results in the coating being damaged and the roofing and substrate continuing to be damaged, all of which would have provided better results if addressed properly in the first place.