Silicone roof coatings on commercial roofs

A silicone roof coating is a fluid-applied layer sprayed or rolled over an existing low-slope roof. When the roof underneath is sound and dry, a coating can add weather protection and reflectivity without a tear-off. It is a restoration of the existing roof, not a new roof system. Coating, recover and replacement are different things; see how they compare.

The first question: is the roof a candidate?

A coating can only be as good as the roof under it. Conditions that usually rule it out as the primary solution include:

• Wet insulation. Coating over saturated insulation seals water in. GAF’s commercial guidance calls for a moisture survey and says a complete tear-off may be the better answer when a large share of the roof is wet.
• Damaged or unsafe deck.
• Repeated leaks with no known source.
• Widespread membrane or seam failure, or loss of adhesion.
• Unresolved ponding or blocked drains. Some coatings tolerate ponding better than others. Check the specific product’s limits.
• Incompatible or failing existing coatings.
• Extensive rust or fastener failure on metal roofs.
• Warranty conflicts with an existing roof warranty.

Our coating feasibility check screens for each of these. It will not recommend coating when any is reported.

Coverage, thickness and warranty

Manufacturers tie the warranty term to how much coating goes on. In GAF’s liquid-applied manual, its silicone system examples step from about 1.5 to 2.0 to 2.5 gallons per 100 sq ft for 10-, 15- and 20-year terms. Dry-film thickness rises with each step. Other manufacturers publish their own tables. Use the specific system’s numbers, not a general rule.

Surface preparation, primers, base coats and seam reinforcement are extra material and labor on top of the finish coat.

Weather windows

Each product lists its own application limits. Henry’s Pro-Grade 988 page states an application range of 35°F to 120°F. Rust-Oleum’s 995 guidance lists 50°F to 110°F, humidity limits, dew-point clearance and a rain-free period. In Ohio and Michigan, these limits shorten the working season. Confirm the window against the product data sheet for your roof.

Example: CertainTeed SMARTCOAT

CertainTeed’s SMARTCOAT line includes acrylic and silicone coatings. It is a useful example of how coating warranties work. (The company our founder works for installs CertainTeed coatings; see our disclosures.) CertainTeed publishes limited warranty terms of up to 20 years for certain SMARTCOAT systems. The term you can get depends on the product and the dry-film thickness applied, which is set during project planning. Its warranties require a CertainTeed-certified contractor, and failing to maintain the roof can void them. Other manufacturers work the same way with their own tables. Before you sign, ask for the specific system, the gallons per 100 sq ft, the warranty term, and the manufacturer’s maintenance requirements in writing.

What a coating project costs

Coating cost depends on the substrate, the preparation, repairs, detail work, the manufacturer system and warranty, and access. The commercial roof cost planner applies our provisional per-square-foot settings for the coating system plus a separate allowance for cleaning, preparation and minor repairs, with a project minimum. Those are early budgeting numbers, not quotes, and they only apply if the roof qualifies. The coating feasibility check screens for the conditions that rule a coating out.

Run your numbers