Silicone & acrylic roof coatings
Flat roof coating in Philadelphia
A coating is a seamless liquid membrane applied over the roof you already have. On a dry, sound flat roof it can add 10 to 15 years. On a wet or worn-out roof it just hides the problem. Call to have a local roofer check which one you have.
The two main options
Silicone vs acrylic on a Philly flat roof
Both are rolled or sprayed on in thick coats and both reflect summer sun. They behave differently once they're up there.
| Compared | Silicone | Acrylic |
|---|---|---|
| Standing water | Holds up to ponding without breaking down | Softens and wears where water sits, so low spots need fixing first |
| Weather to apply | More forgiving of cool, damp days | Needs warm, dry weather to cure, so it's a late-spring-to-early-fall job here |
| Staying white | Picks up dirt over time, which dulls the reflectivity | Tends to stay brighter and cleaner |
| Future recoats | Generally only silicone sticks to silicone | Can be cleaned and recoated with acrylic |
| Foot traffic | Slippery when wet; not ideal under a deck path | Firmer surface, but scuffs where people walk |
Product lines vary. Ask the roofer which coating they're proposing and why it suits your roof.
Who it's for
Is your roof a candidate?
A coating protects a roof that still works. It doesn't rebuild one that's failing. On Philadelphia rowhomes, the deciding question is almost always what's under the surface.
Usually a good fit
- Rubber (EPDM) or modified bitumen roofs that are aging on the surface but still tight at the seams and dry underneath.
- Silver-coated tar roofs with a single layer that's sound, where the owner is tired of repainting every few years.
- Top floors that bake in July. A white coating on a dark roof can make the bedrooms under it noticeably cooler.
- Back-building roofs in decent shape, coated at the same time as the main roof.
Usually not a fit
- Wet insulation or soft, spongy areas when you walk on it
- Two or more old roofs already stacked up
- Widespread blistering, shrinking or open seams
- Gravel-surfaced roofs, unless the gravel is removed first
- Roofs leaking in several places at once
Signs it's time to decide
If you're seeing these, ask about coating while it's still an option:
- Chalky, faded or cracked surface on a rubber roof
- Silver paint peeling and showing black underneath
- Small surface cracks, but no leaks yet
- The roof is 10 to 20 years old and you'd rather not replace it yet
- Top-floor rooms that stay hot long after sundown
Before anyone quotes a coating
Why moisture testing comes first
Coat over wet insulation and you seal the water in. It keeps rotting the boards underneath, and when the sun heats the roof, trapped moisture can push the coating up in bubbles. That's the most common reason a coating fails early.
A careful roofer checks before recommending one. Methods include a moisture meter across the surface, an infrared scan in the evening, when wet areas hold heat longer, and small core cuts that show exactly what's under the top layer. Wet sections get cut out and replaced before any coating goes down.
Be cautious of anyone who offers to coat your roof without walking it or checking for moisture first, especially over a roof that's already leaking.
The work
What a roof coating job involves
Clean & dry out
The roof is power washed, loose material is scraped off, and the surface has to dry fully before anything else happens.
Repair first
Blisters are cut and patched, open seams sealed, flashing at walls and vents fixed, and any wet sections replaced.
Reinforce & prime
Seams and flashing get reinforcing fabric bedded in coating. Rubber roofs and some other surfaces need a primer so the coating bonds.
Coat the roof
The coating goes on in one or two thick coats to the thickness the manufacturer specifies, then cures. Rain right after application is the enemy.
With upkeep, a coated roof can be cleaned and recoated later, adding years again without a tear-off.
Planning your job
What affects the price
Two roofs of the same size can need very different coating jobs. The main factors:
- How much repair comes first. Seams, blisters, flashing and wet sections all have to be fixed before coating.
- The existing surface. Gravel, loose granules or peeling silver paint mean more prep.
- Which coating and how thick. Silicone or acrylic, one coat or two, and whether primer is needed.
- Roof size and shape. Including the back-building roof and any separate porch or addition roofs.
- Penetrations. Skylights, hatches, vents and condensers each need detail work.
- Access. Getting equipment up three stories without a rear alley takes more time.
See whether a coating fits your situation with the Roof Problem Checker.
Related pages
- Repair, coat or replace?: the rule of thumb for deciding
- Flat roof replacement: when a coating isn't enough
- South Philly flat roof repair: blocks full of silver-coated roofs
- North Philly flat roof repair: layered roofs and what's under them
- Roof leak repair: fix active leaks before any coating
Rowhome tip: a coating stops at your property line. Ask how the roofer will finish the edge where your roof meets your neighbors' so water can't get under it.
Roof coating questions
Is a roof coating the same as the silver paint on my roof?
No. Silver (aluminum) roof paint is a thin reflective layer that mainly protects tar from the sun and needs redoing every few years. A silicone or acrylic coating is applied much thicker, forms its own waterproof membrane, and is meant to last for years.
Can a coating stop a leak?
Not by itself. The leak's source has to be found and repaired first, and any wet material replaced. Coating over an active leak usually traps water and makes the problem harder to find later.
Should I choose silicone or acrylic?
If water tends to sit on your roof after rain, silicone usually holds up better. If the roof drains well and you want a surface that stays bright and is easy to recoat, acrylic is often a good choice. The roofer should explain why they're recommending one over the other for your roof.
Can a roof be coated in winter?
Most coatings need dry conditions and mild temperatures to cure, so Philadelphia coating work is mostly done from late spring through early fall. Silicone is more tolerant of cooler weather than acrylic, but no coating should go on a wet or frosty roof.
How do I keep a coated roof in good shape?
Keep drains and gutters clear, keep foot traffic to a minimum, and have it looked at every couple of years. Small damage can be patched with the same coating, and when the surface wears thin, it can be cleaned and recoated.
Have a different question about coating your roof? Call and ask a local roofer.
(215) 702-6130