Effective Flat Roof Drainage Solutions

Pooling water on a flat roof can cause problems such as pulled away flashing, popped nails, exposed railheads and the washing away of gravel or stone from the shingles. These problems could cause the roof to leak and severely damage the roof deck, underlying structure and interior finishing. Water leaking through the roof could also cause fire and electric hazards.

There are several flat roof drainage solutions available to avoid these problems.

Scupper Drains

Scupper drains are an economical drain system that can be installed in low edge areas to reduce water pooling. They're galvanized drains that are attached to the roof edges and they work by guiding water from the edge of the roof down to the water downspouts.

Internal Drains

Internal drains are another affordable drainage solution option that can also tie into existing home drain systems. They require the installation of aluminum or copper inserts into areas of the roof where water pooling commonly occurs. Plumbing systems are attached to the drain inserts to guide the water outside the building through a sidewall. Pipes run down an inside wall and are hung underneath the roof decking through the rafters. To be effective, this system should be installed by a licensed plumber.

Eavestrough Drainage

Although not commonly used anymore, the eavestrough drainage system is a good option if you have an older large industrial or commercial flat roof. Drainage ditches are created in the roof in the lower insulated areas. These ditches guide water toward the eavestroughs.

Drainage Helpers

Drainage helpers are a good option if you already have a good flat roof drain system, but want to provide your system with the ability to move more water if need be. This system works by recessing insulation in installed drains to allow for faster water drainage.

True Sloped Insulation

True sloped insulation is a very expensive flat roof drainage solution. Since it's installed underneath the flat roof, this drainage solution is typically used only with new roofs.

First measurements of the roof are taken. Then insulation, made out of the ISO board, EPS board or wood fiber board, is pre-cut by the manufacturer to the roof's exact measurements. A slope pattern is created based on the size of the roof, then skilled technicians install the slope to create a perfect ramp that guides the water away from the roof's surface. The roof system is then installed.

Step Sloped Insulation

Step sloped insulation is a more affordable way to slope a flat roof and it involves installing several layers of flat board insulation under the roof membrane instead of cutting a custom-made roof board. The board is installed in steps with the thinnest boards at and around the drains. Then the roof membrane is then installed over the step sloped insulation.

Plant Carriers

Installing a plant carrier to soak up any pooling water is an economical and eco-friendly way to enhance drain system that's already in reasonable shape.

Plant carriers have a carrier element, usually a netting of biodegradable fibers or plastic, where seeds or seedlings are planted. The roots anchor in the netting and suck moisture from the roof. Water not used by the plants is whisked away by the current drain system.