Maintaining Drainage on Flat Commercial Roofs

While flat roofs offer low construction and repair costs, they are more susceptible to cracks, leaks, and blisters. This roof is also very prone to clogging, which causes leakage. Therefore, if you are planning to have a flat roof on your commercial building, you have to find ways to maintain proper drainage on the roof.

If stagnant water stays on your flat roof for a long time, it will cause severe damage that can eventually lead to the collapse of the entire roof. Here are several effective ways to maintain drainage on your flat commercial roof.

Easy Ways to Drain a Flat Commercial Roof

Install Inner Drains

Inner drains placed under the roof or inside the parapet wall help to get rid of rainwater, ensuring that there are no pools of water stuck on your flat roof. The good thing is that roofing experts have discovered ways of concealing these drains to ensure no pipes are visible. Since these pipes are inside the concrete slab or walls, they create enough space on your flat roof that you can use for other purposes, such as creating a rooftop garden. Even if your roof leaks, the water won’t cause any damage to your building because the internal drains will drain it.


Scuppers are the openings created in the wall side to carry water from the roof to the gutters or downspouts. They are typically used together with internal drains to prevent water from damaging the walls. You should also use them along with a collector’s head to prevent water from coming into contact with the walls.

One of the benefits of using scuppers is that they are more affordable than inner drains. If your scuppers are wide enough, leaves and small twigs won’t get stuck inside to clog the drainage system. And because you have a collector, no debris will block the flow of water.


Also referred to as the conductor pipe, a gutter is a trough installed on the flat roof edges to drain excess water. For your gutters to drain the roof properly, you have to create a slope. Also, make sure the slope is appropriately maintained. The durability of your gutter depends on the material you choose. The most common materials for making gutters include galvanized steel, aluminum, and vinyl.

Siphonic Roof Drains

This type of drain removes water from a flat roof through siphoning. It passes water faster than other flat roof drainage systems. In a siphonic drainage system, all pipes are placed horizontally, allowing water to pass quickly. So, it eliminates the need to have a slope.