Commercial Roof Drain Cleaning and Repair

Atlanta delivers 53 inches of rain per year in high-intensity events. A partially clogged drain on a flat commercial roof is not a nuisance - it is the reason the building is leaking.

Atlanta's rainfall pattern is more stressful on commercial flat roof drainage than the annual total suggests. The city's 53 inches per year are not delivered steadily - they arrive in concentrated thunderstorm events, predominantly from April through September, that can dump 2 to 3 inches in a single hour. A 20,000-square-foot flat roof receiving 2 inches of rain in one hour accumulates over 24,000 gallons of water in 60 minutes. If the drainage system is not running at full capacity, water backs up, finds every seam imperfection at height, and produces leaks that disappear when the storm passes - leaving the building manager convinced the roof is fine until the next storm.

Commercial roof drains fail in two ways: they get clogged, and they deteriorate. Clogging is the more common and more preventable failure mode. Roof drains collect leaves, HVAC filter debris, bird nesting material, granules from aging modified bitumen roofs, and wind-blown debris year-round. In Atlanta, the combination of the city's urban tree canopy - mature hardwoods in Buckhead, Midtown, Morningside, and Virginia-Highland contribute significant leaf load to commercial roofs adjacent to Atlanta's residential neighborhoods - and the summer thunderstorm sediment load means drain maintenance is not optional.

Drain deterioration is the second failure mode: cast-iron drain bodies on older Atlanta commercial buildings (1960s through 1980s construction) corrode from below as the interior riser pipe corrodes and backs up. On these buildings, the symptom is ponding that does not clear after a storm even with the drain strainer clean - the restriction is inside the pipe, not at the surface. We inspect the full drain assembly, including the interior drain riser where accessible, to distinguish surface clogging from internal pipe restriction.

Strainer cleaning and inspection: The drain strainer - the dome or flat grate that prevents debris from entering the drain body - is the first line of defense. Strainers clog and restrict flow long before they are completely blocked. We clean strainers, inspect them for rust, cracking, or missing sections, and replace any strainer that is not functioning as a debris barrier. Strainer replacement is a low-cost item that prevents the far more expensive consequence of drain body clogging from debris that bypasses a compromised strainer.

Drain bowl cleaning: Below the strainer, the drain bowl collects sediment, granules, and debris that pass through or bypass the strainer. We remove accumulated sediment, inspect the drain body interior for corrosion, and verify that the drain clamp ring - which secures the membrane to the drain body - is intact and watertight. A loose or corroded clamp ring is a water entry point at the most sensitive location on the roof.

Flow verification: After cleaning, we verify flow by flooding the drain bowl with water and timing the drain rate against the expected capacity for the drain size. A 4-inch interior drain should handle approximately 50 gallons per minute at design head. If flow is significantly below that, the restriction is inside the pipe, not at the surface - we flag this and recommend internal inspection.