Flat Roof Coating for St. Louis Homes, Garages and Porches
Category
A flat roof coating is a liquid-applied, continuous layer that seals and protects the low-slope roofs on homes, detached garages and porches. Applied over a sound roof, it closes up seams, covers flashing edges and reflects summer sun. In St. Louis and Webster Groves, early fall is a smart window to get it done before freeze-thaw season.
Most houses around here have at least one flat roof somebody forgot about. The porch roof on a brick bungalow in Webster Groves. The garage out back with roll roofing that's older than the car parked in it. The rear addition on a 1960s ranch in Florissant. Those small roofs leak quietly for a long time before anyone notices the stain on the ceiling.
Which flat roofs on a house are good candidates for coating?
Small, low-slope roofs that are aging but still dry and solid underneath. If the roofing is tired but the deck is sound, a coating is often the most practical fix.
- Flat or nearly flat porch roofs, common on older St. Louis brick homes
- Attached and detached garages with roll roofing or modified bitumen
- Rear additions, sunrooms and enclosed porches
- Carports and breezeways
- Low-slope metal roofs on sheds and workshops
Our page on flat roof coatings for Missouri homes covers the Super Shield system Rhino Shield of Missouri uses on them.
Why do small flat roofs leak?
Almost always at the seams, the flashing and the low spots. Leaks rarely start in the open middle of the roof.
Roll roofing and modified bitumen are laid in strips, and every lap is a joint that can open as the roofing dries out and shrinks with age. Where a porch roof meets a brick wall, water depends on flashing tucked into the mortar joints, and on a lot of older homes that mortar has been crumbling for years. Pipe vents, skylights and the edge where the roof drains into a gutter are the other usual suspects.
How are seams and flashing handled before a flat roof is coated?
They get repaired and reinforced first. The coating goes over the details; it doesn't replace them.
- Clean the surface. Leaves, moss, dirt and loose granules come off, and the roof has to dry completely.
- Repair the roofing. Blisters get cut out and patched, and open laps get re-adhered.
- Reinforce seams. Laps and joints get seam tape or reinforcing fabric set into a base coat.
- Address the flashing. Loose flashing gets re-secured and sealed. If the mortar it's tucked into is failing, that masonry needs repointing before any coating goes on.
- Detail penetrations. Vent pipes, curbs and drains get extra attention, since they move differently than the roof around them.
- Apply the coating in multiple coats to the specified thickness.
Step four is where shortcuts happen. Smearing coating over a gap between a porch roof and a brick wall might stop a drip for one season, but the wall keeps moving and the gap comes back. If you want to understand how wall-to-roof flashing is supposed to be built, Fine Homebuilding has solid detail on it, and it's worth a read before you talk to any contractor.
What about drainage on a flat porch or garage roof?
The water has to have somewhere to go. A "flat" roof should still have a slight pitch toward a gutter, scupper or drain, and if it doesn't, a coating alone won't solve the problem.
On these small roofs, drainage problems are usually simple ones. Gutters clogged with leaves back water up under the roof edge. A drip edge that's bent or missing lets water curl back under the roofing. A joist that's sagged over the years creates a low spot where water sits after every rain.
October makes the gutter part worse. Leaves are coming down now, and a porch gutter can fill in a single windy week. If you notice water standing on the roof a day or two after a storm, tell your contractor. It may mean a framing fix, and it changes what product goes on.
Is fall a good time to coat a flat roof in St. Louis?
Early to mid fall usually works well, as long as the days stay warm and the rain holds off long enough for the coating to cure. Once nights turn cold, the window closes until spring.
Most liquid roof coatings need dry surfaces and air and surface temperatures comfortably above freezing, often around 50°F and rising, for a good stretch after they go on. The product's data sheet sets the exact numbers. Fall adds a wrinkle: heavy morning dew. Crews usually start later in the morning so the roof is truly dry, and they stop early enough that the coating can set before the evening dew settles.
The reason to beat winter is simple. Missouri freeze-thaw cycles work water into every open seam, expand it and pry the gap a little wider each time. Snow and ice sit on flat porch roofs longer than on anything sloped. A roof that goes into winter with its seams sealed is in much better shape come March. For the rest of the house, our guide to preparing your exterior for winter covers what else to check.
Should I coat, patch or replace my flat roof?
It depends on whether the problem is the surface, one spot or the structure. Here's how we usually sort it out on a residential roof.
| What you're seeing | Usual best fit |
|---|---|
| One small leak at a vent pipe, roof otherwise solid | Targeted repair |
| Roofing aging and drying out, seams starting to open, deck sound | Repair seams, then coat |
| Water stains but a dry, solid deck | Find and fix the leak source, then coat |
| Soft or rotted decking, wet insulation | Repair or replace the deck and roofing first |
| Water standing for days from a sagging joist | Fix the framing, then decide |
Super Shield roof coatings carry a 10–15 year warranty, and that warranty only means something if the roof underneath is sound. You can compare the flat, sloped and white options on the Super Shield roof coating page.
Careful prep is what homeowners notice most about our crews, on walls and roofs alike. This review came from a homeowner after we coated the outside of his house:
"Team does an excellent job. Very focused on doing things right. Did so well our neighbor whom observed the work hired them 6 months later to do their home."
— Mark S.
That was a wall coating job, not a roof. "Focused on doing things right" is still the whole point on a porch roof, where the seams and flashing decide whether the coating holds.
Frequently Asked Questions
Can you coat a flat roof in the fall?
Yes, in early to mid fall, as long as temperatures stay above the coating's minimum and the roof is dry. Crews work around morning dew and watch the forecast for rain. Once nights get consistently cold, most coating work waits until spring.
How long does a flat roof coating last?
That depends on the roof underneath, how well the seams and flashing were prepped and how well the roof drains. Super Shield roof coatings from Rhino Shield of Missouri carry a 10–15 year warranty. A well-kept coated roof can usually be recoated later instead of replaced.
Can you walk on a coated flat roof?
Occasional foot traffic for cleaning gutters or checking the roof is normal. A coated porch or garage roof isn't meant to be used as a deck, though. If you plan to walk on it regularly or set things on it, ask about walkway protection before the job starts.
Do I need to replace my flat roof before coating it?
Not if the deck is solid and the roofing is dry underneath. Damaged spots, blisters and open seams get repaired as part of prep. If the decking is soft or the insulation is wet, those areas have to be fixed or replaced first, because a coating would trap that moisture.
Get Your Flat Roof Ready for Winter
If your porch roof, garage or addition is showing open seams or water stains, there's still time to look at it before cold weather sets in. Request a free estimate or call 314-239-7947 and we'll tell you whether coating, repair or replacement makes sense.
