Silicone is the coating you pick when water sits on the roof. Most coatings and many membranes degrade under standing water. Silicone does not, which makes it the practical choice for a flat roof with low spots and a long, wet spring thaw. In Coeur d'Alene, ID, where spring melt can sit on a flat roof for days, that matters. The bid still lives or dies on prep, not on the product.
We price the coating, the prep and the repair list on separate lines, because the coating is the smallest part of the work.
The Call: When a Coating Replaces a Replacement
A coating makes sense when the roof is dry and sound and the surface is tired. The membrane has weathered, the seams hold, the insulation is dry and the owner wants to extend life without a tear-off. A silicone coat adds a waterproof, reflective layer and defers replacement for years. It makes sense on roofs with ponding, because silicone tolerates standing water better than most alternatives.
It does not make sense over wet insulation, over a failing deck or on a roof with widespread seam failure. A coating cannot fix those and will trap the moisture. We scan and core before we recommend one, and we show the alternate: a replacement or a recover priced beside the coating, so the owner sees both.
Age of the existing roof is the other test. A roof near the end of its life with a dry core can often take one coating, but not a second. We tell the owner how many years the coating is expected to add and what the next decision looks like. Buying five more years with a coating is a good deal if the money saved goes into a replacement fund and not into the next patch.
What It Costs: Prep, Repairs and Coverage
Prep is the cost center. The roof is power washed, loose material is removed, rust is treated on metal, and every seam, flashing and penetration is repaired. Then a primer goes on where the substrate needs one, followed by the silicone at the thickness the maker requires. Coverage rate and number of coats set the material line. Labor depends on roof size, access and the number of details.
We list the repair count as its own line with a unit price per seam foot, per flashing and per penetration. That is where the final number grows, and a bid that hides it is the one that returns with a change order. The cleaning step is the first task in roof coating restoration, because silicone bonds to a clean surface and not to dirt.
Reflectivity is a bonus, not the reason to buy. A white silicone surface reflects heat in July and does little under snow, so we do not count energy savings in the price. If the owner wants a number, we use the building's cooling load, as laid out in our cool roof installation work.
Ponding: What Silicone Handles and What It Does Not
Silicone holds up under standing water, so a pond does not destroy the coating the way it can destroy others. It does not remove the pond. Standing water still loads the structure, grows algae, collects dirt and freezes in winter. The coating protects the membrane from the water. The slope or the drain has to fix the water.
Where the ponding is shallow and minor, we coat and accept it. Where it is deep or constant, we recommend tapered insulation, an added drain or a scupper to drain it, and we price that work as an alternate. Frozen ponds are a winter issue: a sheet of ice on a silicone surface is slippery and can pull at the coating edges. We keep drains clear and check the low spots after the thaw.
Drains deserve a closer look than the coating does. We reset sumps, replace strainers and make sure the coating wraps the drain flange without bridging it. A coating that closes off the edge of a drain ring is a coating that will peel there first. Scuppers get the same detail.
What the City Sheet Says: Snow, Wind and Ice
A coating adds almost no weight, which helps on an older structure, and it does not change the snow the roof must carry. It also does not change wind resistance, because the coating is only as secure as the roof it covers. A membrane with loose fasteners or a lifted edge needs repair before it is coated.
Silicone stays flexible in the cold, which helps it ride through a swing that runs from a January mean near 31 F to summer days above 90 F. We confirm the substrate is dry and the temperature is in range before each coat.
Fire and slip ratings sit in the same file. A coating that lowers the roof's fire classification can cause trouble at the permit counter, so we confirm the coated assembly's rating with the maker before we order. On service routes we add granules to the final coat, because a smooth, wet silicone surface is slick under a boot.
Where It Fits: Metal, Single-Ply and Old Built-Up Roofs
Silicone goes over several substrates: sound single-ply sheets such as TPO, metal roofs, modified bitumen and built-up roofs, with the right primer for each. Large, low-slope roofs in Post Falls and along the I-90 corridor are worth a look when they pond. West in Spokane Valley, annual precipitation is a bit over 16 inches, drier than Coeur d'Alene, and we size the drain plan to the weather on each side.
We check the old surface before we choose. A roof that was coated with acrylic cannot take silicone without special prep, and silicone cannot be recoated with other products later. That makes the first choice more permanent than it looks. For comparison we price acrylic beside silicone on roofs where ponding is not a concern.
Schedule: Dry Days Above the Cure Minimum
Silicone cures by reacting with moisture in the air, and it needs a dry surface and a temperature above the maker's minimum. Rain within hours of application can wash it. We aim for late spring through early fall, check the forecast for the next day, and plan a clean, repaired roof ahead of the coating crew. On occupied buildings the odor during cure is mild, but we still shield air intakes. The record low of minus 30 F reminds everyone that a coating job is not a winter job.
Closeout is a walk with the GC and the owner: thickness readings at marked spots, photographs of every seam and drain, and the maker's coating warranty. The owner also gets a wash and inspection schedule, because a coating that is cleaned and checked lasts longer than one that is ignored.
Commercial Roofing Questions
Why silicone over acrylic?
Silicone handles standing water. Acrylic does not like it. If the roof ponds, silicone is the safer pick.
Does silicone get dirty?
Yes, it attracts dirt, and the surface dulls. Washing restores some reflectivity. We note this in the bid.
Can we recoat silicone later?
Only with silicone, in most cases. Other coatings do not bond to it. The first choice limits the next.
Is it slippery?
Wet or icy, yes. We add granules or walkway pads on service routes.
How long does a silicone coat last?
It depends on the thickness, the substrate and the care. A thicker coat on a clean, sound roof lasts longer. We give the maker's term, not a promise.