Video · Maintenance & ponding
Fixing Ponding Water on a Low-Slope Roof
Watch “How to Fix Ponding Water on a Commercial Roof” on YouTube (opens in new tab)
- Mod bit
- Built-up
- TPO
- PVC
- EPDM
What this video shows
A roofing contractor explains how ponding water is fixed on a commercial low-slope roof. The same logic applies to flat-roof homes: get the water moving off the roof first, then decide whether the low spot needs building up or the roof needs more slope.
Key points
- The common rule of thumb: water still sitting 48 hours after rain is ponding, and it shortens the life of most roofs.
- Start with the cheap fixes: clear drains, scuppers and gutters of leaves and debris.
- Real fixes add slope or outlets: tapered insulation, crickets, or extra drains and scuppers. That's usually a roofer's job.
- Some silicone coatings are rated for ponding water, but coating a sag doesn't remove the weight or the cause.
- A sagging deck can mean structural damage. Have it checked before adding material.
Products in this video
The products used or shown, or the closest match we could verify. Typical price ranges, not live prices.
Floor squeegee · $15–$30
LibmanLibman 515 Floor Squeegee, 24 in.
- Size
- 24 in.
- Mod bit
- Built-up
- Rolled
- TPO
- PVC
- EPDM
- Spray foam
- Metal
- Silicone-coated
- Acrylic-coated
Pushes standing water toward a drain so a low spot can dry out for inspection, patching or coating.
Read the fine print: Moving water off a roof is maintenance, not a fix. If the same spot ponds after every rain, it needs slope or a drain.
Best for: Clearing ponded water before repairs or coating
Check price on Amazon for Libman 515 Floor Squeegee, 24 in. (opens in new tab)Affiliate link — we may earn a commission at no extra cost to you. Coverage and specs are the manufacturer's stated figures. Disclosure
Wet/dry vacuum · $90–$140
CRAFTSMANCRAFTSMAN CMXEVBE17590 9 Gallon Wet/Dry Vac
- Size
- 9 gal
- Mod bit
- Built-up
- Rolled
- TPO
- PVC
- EPDM
- Spray foam
- Metal
- Silicone-coated
- Acrylic-coated
Pulls standing water out of low spots and drain sumps so you can inspect, patch or coat the same day.
Read the fine print: It needs power on the roof, so use a GFCI-protected outdoor cord and keep the connections out of the water. Take out the dust bag before wet pickup.
Best for: Removing ponded water before repairs or coating
Check price on Amazon for CRAFTSMAN CMXEVBE17590 9 Gallon Wet/Dry Vac (opens in new tab)Affiliate link — we may earn a commission at no extra cost to you. Coverage and specs are the manufacturer's stated figures. Disclosure
Cordless leaf blower · $120–$180
DEWALTDEWALT 20V MAX XR Cordless Leaf Blower (DCBL722B, tool only)
- Mod bit
- Built-up
- Rolled
- TPO
- PVC
- EPDM
- Spray foam
- Metal
- Silicone-coated
- Acrylic-coated
Cordless, so there's no cord dragging across the roof. Use it to clear drains and scuppers, and to blow off dust right before primer or coating.
Read the fine print: Tool only: the battery and charger are sold separately. Watch your footing, and don't walk backward while you blow.
Best for: Clearing leaves from drains and the final dust-off before coating
Check price on Amazon for DEWALT 20V MAX XR Cordless Leaf Blower (DCBL722B, tool only) (opens in new tab)Affiliate link — we may earn a commission at no extra cost to you. Coverage and specs are the manufacturer's stated figures. Disclosure
Stiff push broom · $25–$45
LibmanLibman 825 Rough-Surface Heavy-Duty Push Broom, 24 in.
- Size
- 24 in.
- Mod bit
- Built-up
- Rolled
- TPO
- PVC
- EPDM
- Spray foam
- Metal
- Silicone-coated
- Acrylic-coated
Stiff bristles clear loose granules, grit and leaves off a flat roof before you wash, inspect or coat.
Read the fine print: Go easy on old mod bit. Scrubbing hard strips granules you want to keep.
Best for: Sweeping debris and loose granules before inspecting or coating
Check price on Amazon for Libman 825 Rough-Surface Heavy-Duty Push Broom, 24 in. (opens in new tab)Affiliate link — we may earn a commission at no extra cost to you. Coverage and specs are the manufacturer's stated figures. Disclosure
Silicone roof coating · $280–$400
GacoGacoRoof 100% Silicone Roof Coating, White (GR1600)
- Chemistry
- Silicone
- Size
- 4.75 gal (sold as 5 gal)
- Coverage
- 100 sq ft per gal per coat (about 11 dry mils on a smooth surface); Gaco calls for at least two coats, more on textured surfaces
- Mod bit
- Built-up
- Rolled
- Metal
- Spray foam
- Silicone-coated
- Acrylic-coated
A silicone that contractors use and that is also sold retail. Plan on two full coats to reach the film build Gaco specifies; like other silicones it handles ponding areas better than acrylic.
Read the fine print: Gaco says to recoat GacoRoof only with more GacoRoof, and to run its adhesion test (or prime with its E5320 epoxy primer) on aged asphalt to head off bleed-through. Not for shingles. It's solvent-based, so expect odor and keep it away from open air intakes while you work.
Best for: Full-roof silicone restorations where you'll put down two proper coats
Check price on Amazon for GacoRoof 100% Silicone Roof Coating, White (GR1600) (opens in new tab)Affiliate link — we may earn a commission at no extra cost to you. Coverage and specs are the manufacturer's stated figures. Disclosure
Read the full guide
Maintenance & ponding How to fix ponding water on a flat roof Water that is still on a flat roof 48 hours after rain is ponding, and it means the roof isn't draining the way the building code intends. Start by clearing drains, scuppers and gutters; if water still sits, the fix is usually a roofer adding slope (tapered insulation or crickets) or adding drainage. Small spot fixes often run $500–$2,500, while tapered insulation added during a reroof typically adds $2–$5 per sq ft of treated area.Video by Sol Vista Roofing, embedded from YouTube. The summary, key points and cautions on this page are our own; Sol Vista Roofing doesn't endorse TheFlatRoofPro.com or the products listed. Roofing work for hire generally requires a licensed roofing contractor.