Flat Roof Coating in Florida: When Does It Work?

What is a flat roof coating?

A flat roof coating is a liquid that dries into a waterproof, sun-reflecting skin over the roof you already have. It is a way to renew a sound roof, not a new roof.

The Roof Coatings Manufacturers Association (RCMA) says a coating becomes "the first layer of UV and waterproofing protection for the roof." It is rolled or sprayed on, then cures into one continuous layer. The RCMA says almost all types of roofs can be coated, with ballasted and gravel-surfaced roofs the usual exceptions.

The two coatings you will hear about most are acrylic and silicone. A Florida Roofing and Sheet Metal Contractors Association (FRSA) technical article by an APOC product manager also lists asphalt-based aluminum coatings and SEBS coatings. The same article says some roofs can't be coated at all, and others can be coated only if certain conditions are met.

Why do homeowners and building owners ask about coatings? A coating skips the tear-off. The FRSA article says a reinforced coating restoration is usually less costly and takes less time than tearing a roof off. That is a real advantage on a roof that qualifies. The trouble is that many roofs that get quoted a coating do not qualify.

This page explains how coatings work so you can judge a quote. If you want to know what shape your flat roof is in, a roofer can look at it and write up what the photos show. See our flat roofing page for what Coastline does on low-slope roofs.

When does a coating hide problems instead of fixing them?

A coating hides problems when it goes over wet insulation, active leaks, ponding water or a roof that is already worn out.

A coating is a thin film. It can't dry out a wet roof, and it can't find a leak. Here is where it goes wrong.

Wet insulation sealed in

The Gaco silicone sheet says to let the roof dry completely after cleaning, "to prevent blistering," and to check that residual water has dried before coating. Water trapped under a coating has nowhere to go, so the sun heats it and it pushes up as blisters. The Florida Building Code, Existing Building, Section 706.3 says new roof coverings can't go over a roof that is water soaked or has deteriorated. The rule also calls for tear-off when a roof has two or more layers already.

Leaks that were never traced

The FRSA article is blunt: coating an area without finding the leak source "is not a long-term solution." It says to find leaks first and repair them with reinforcement, such as fabric and sealant, because a reinforced repair performs far better than an unreinforced one.

Ponding the coating can't handle

The Gaco acrylic sheet says plainly that it is not for surfaces prone to ponding water. Silicone tolerates standing water, but that does not make ponding harmless. Our guide on ponding water on a flat roof covers why the water collects and what fixes it.

A roof that is past its life

If the surface is cracking like dried mud, the roof may be past the point where a coating helps. InterNACHI, the home inspectors' association, defines alligatoring as aged asphalt that has lost its volatile oils to sun and solar radiation. Read alligatoring on a flat roof before you accept a coating quote on a roof that looks like that.

A coating also can't add back what age has taken. When the membrane is splitting, see flat roof splits and cracks and compare it with a replacement in the best flat roof material for Florida guide.

How long does a flat roof coating last, and when is replacement the better call?

The RCMA says a properly applied coating can extend roof life up to 10 years or more. It depends on the coating, the conditions and how thick it was applied.

InterNACHI's life expectancy chart lists aluminum coating at 3 to 7 years. The RCMA says most coatings can be renewed as they wear. So a coating is not a one-time fix. It is a maintenance cycle that has to be planned and paid for again.

Dirt matters here, too. The Department of Energy and Lawrence Berkeley National Laboratory guide says a dirty cool roof reflects less sunlight, though annual cleaning can restore up to 90 percent of the starting reflectance.

Replace instead of coating when the insulation is wet, the roof has several layers, the membrane is splitting, or the same spot keeps leaking. Coastline's flat roof work is TPO, and the choice comes after a look at the roof. We do not set a price in an article. The flat roof cost guide shows what shapes it, and the flat roof lifespan guide shows how long each type tends to last.