Roof Coatings: Advantages and Disadvantages

Roof coatings are sold hard, and some of the pitch is true. The way to decide is to weigh both columns against your actual roof. Here is the honest version of each.

The advantages

• Cost. No tear-off, no disposal and far less labor. A coating system typically costs a fraction of a replacement on the same roof.
• No disruption. The building stays open. There are no dumpsters, no exposed deck, and no day when the roof is off and the forecast matters.
• Speed. Most roofs are coated in days.
• Seamless waterproofing. The membrane is applied as a liquid, so it has no seams of its own. Seams and fasteners, where most roofs leak, are sealed under one layer.
• Lower cooling bills. A white reflective roof runs far cooler in summer than a dark one, which cuts air-conditioning load and eases wear on rooftop units.
• Renewable. When the coating wears, it can be cleaned and recoated. Done on schedule, that cycle can keep a roof in service for decades.
• Less waste. The old roof stays out of the landfill.
• Accounting treatment. A coating is often treated as maintenance rather than a capital expense. Ask your accountant how that applies to you.
• Manufacturer warranties. Systems installed by approved contractors at the specified thickness carry 10, 15 or 20 year warranties.

The disadvantages and limits

• It cannot fix a failed roof. Wet insulation, a rotten or heavily rusted deck, or a membrane that is coming apart all disqualify a roof. Coating over those problems seals them in.
• Preparation is everything. Most coating failures are adhesion failures caused by a dirty, chalky or damp surface. A rushed wash job shows up as peeling within a year or two.
• Weather sensitive. Coatings have temperature, humidity and rain-window requirements during application and cure. In some regions the season is short.
• Standing water. Acrylic coatings soften and fail where water ponds. Silicone handles ponding, but costs more and limits what can go over it later.
• Dirt pickup. White roofs get dirty, and a dirty roof reflects less heat. Some coatings hold dirt more than others. Periodic cleaning keeps the benefit.
• Thickness is the warranty. If the crew applies less material than the system requires, the warranty is void and you may not know until a claim is denied.
• Contractor quality varies widely. The product rarely fails. The installation does. Choosing the contractor is the biggest decision in the project.
• Removal is costly. A failed coating is hard to strip, and a future contractor has to work around it.

When a coating is the right call

The roof is structurally sound. A moisture survey shows the insulation is dry, or wet areas are small enough to cut out and replace. Leaks come from seams, fasteners, flashings and penetrations rather than from everywhere. You want to defer replacement by ten years or more and would like a cooler building in the process.

When it is the wrong call

Widespread wet insulation. A deck that is rusting through or rotting. A membrane that is shrinking, splitting or delaminating across large areas. A roof that is so uneven water stands in deep pools everywhere. In these cases the honest answer is replacement, or a recover with new insulation, and a good contractor will say so.

How to tell which side your roof is on

Have the roof inspected by someone who does moisture surveys, not just visual walks. Then compare the coating bid against a replacement bid for the same roof. Our qualifying checklist covers what the inspection should include, and coating versus replacement lays out the economics. When you are ready, get free estimates from contractors who do this work every week.