Does a Silicone Roof Coating Change Your Roof’s Fire Rating? UL 790 Class A Explained for Building Owners

A silicone roof coating can keep your roof’s Class A fire rating, and on some older roofs it can be part of an assembly that earns one, but only if the coating is listed for your roof. Fire ratings under UL 790 and ASTM E108 are not printed on a pail of coating. They belong to a tested roof assembly: the deck, the insulation, the existing membrane, the slope, and the coating applied at a specific thickness. Change one of those pieces and the rating can change with it. Before a crew sprays anything, your contractor should be able to name the listed assembly that matches your building.

Most owners never think about this until an insurer or a building inspector asks. Here’s what the rating means, what moves it, and what to have in hand before the job starts.

What Class A, B and C Actually Measure

The International Building Code (IBC Section 1505) requires roof assemblies to carry a fire classification determined by UL 790 or its equivalent, ASTM E108. Both tests set fire to the roof surface from the outside and measure three things:

• Flame spread: how far fire travels across the roof surface.
• Burning brand: whether a burning block of wood landing on the roof (think embers from a neighboring fire) burns through to the deck.
• Intermittent flame: whether repeated flame exposure penetrates the assembly.

Class A is the highest rating, for severe fire exposure. Class B covers moderate exposure and Class C light exposure. Under the 2021 IBC, Section 1509 states it directly: a roof coating applied to an existing roof has to comply with the Section 1505 fire classification requirements. The coating doesn’t get a pass because the old roof was already rated.

Why the Rating Belongs to the Assembly, Not the Coating

The Roof Coatings Manufacturers Association lists the factors that decide a coated roof’s fire class, and only one of them is the coating itself:

• Deck type. Steel and concrete decks are noncombustible. Wood decks are combustible, and it is much harder to reach Class A over them. One major manufacturer’s literature lists its silicone as Class A over noncombustible decks but Class B over combustible decks. Same product, different building, different rating.
• Existing membrane. Coating over modified bitumen, built-up asphalt, TPO, EPDM or metal is tested separately, because the substrate contributes fuel.
• Insulation. Foam insulations can narrow the slope range a listing covers.
• Slope. Most commercial listings are written for low-slope roofs. Steeper sections can need a different listed system.
• Applied thickness. The listing assumes a specific dry-film thickness, and sometimes granules or reinforcement. A crew that runs thin to save gallons can install an assembly that no longer matches the test.

That last point is the one you control through your contractor. The same mil-thickness discipline that protects your warranty (we break down the math in our coverage rate guide) also keeps you inside the fire listing.

The Good News: Coating Can Upgrade an Older Roof

Many existing roofs across Pennsylvania and the Mid-Atlantic are Class B or C, or carry no documented rating at all. Silicone itself is inherently resistant to burning, and listed silicone systems exist for most common substrates. Manufacturer literature for one widely used silicone states that it achieves a UL 790 Class A rating when applied over existing UL-classified Class B or C assemblies on noncombustible decks.

For a typical steel-deck warehouse or retail building, a properly specified restoration can leave you with a documented Class A roof for $3–6 per square foot, against $10–16 per square foot for tear-off and replacement. That’s 50–70% savings, a 1–3 day install on most buildings, and a 20-year warranty. It’s one more reason warehouse owners are choosing restoration.

Why Your Insurer Cares

Commercial carriers increasingly review roof condition and construction at renewal, and fire classification is part of how they underwrite a building. If a coating is installed outside its tested assembly, you may be left with a roof whose fire class no one can document. That’s an awkward position during a claim or a renewal inspection. It’s the same lesson as our post on storm damage and insurance: paperwork you collect at installation is far easier than proof you try to rebuild later.

Keep in mind that the product standard and the fire test are different things. ASTM D6694 tells you the silicone meets minimum physical properties. UL 790 or ASTM E108 tells you how the finished roof behaves in a fire. A good quote documents both.

What to Ask Before the Crew Starts

• Which listed assembly matches my roof? Ask for the UL Product iQ, FM RoofNav or ICC-ES listing number that covers your deck, insulation, existing membrane and slope.
• What class does it carry, and is that what my code requires? Local jurisdictions adopt different IBC editions and can be stricter than the base code.
• What thickness does the listing require, and how will you prove you hit it? Wet-mil readings during application and a documented gallon count are the evidence.
• Will I get it in writing? A one-page letter naming the assembly and its class is something you can forward straight to your insurer.

If a contractor can’t answer the first question, they’re guessing at your fire rating.

Get a Coating Plan That Holds Up to Your Insurer

NoTearOff Roofing’s free roof assessment identifies your deck, insulation and membrane, and we specify a listed silicone system that matches them, so your restored roof comes with a documented fire classification along with its 20-year warranty. Learn how no-tear-off restoration works, or see how long a properly built system lasts with a recoat. We serve commercial buildings across Pennsylvania, New Jersey, Delaware, Maryland, Ohio and West Virginia.

Request your free commercial roof assessment. If your insurer has already asked about your roof’s fire class, mention it and we’ll include the listing in your proposal. Want a number first? Our roof coating savings calculator shows what restoration could save you compared with a full tear-off.