5 Tips for Installing Flat Roof Drainage

Flat roof
  • 4-40 hours
  • Intermediate
  • 100-2,000

Flat roof drainage is a necessity for a home that has a flat, or almost flat, roof. This drainage allows for water to be transported off of the roof so it does not collect in one area.

In the event of a large rain storm, the weight of the standing water can be enough to collapse a weakened roof.

Installing flat roof drainage is a very detailed project that takes a lot of time and planning. If you are thinking about installing flat roof drainage yourself, here are a few tips to keep in mind.

1. Always Create a Sump for Drainage

large house with a flat roof

When there is little slope for the water to actually run off the roof you will need to build in a sump system for the water to travel along.

If there is not a sump built in to the drainage system you will have the same problems you had before the roof drainage system was installed.

The standing water can collect other debris, which can foul up the drainage system. Always make sure you have a sump system built into the roof.

2. Double Check Size of Flat Roof Drain

One of the mistakes that even professional installers make is choosing the wrong drainage system for the roof.

Make sure you take the time to measure your roof and talk with the salesman about the different options.

It is much better to have a drainage system that is a little too large than one that is too small to handle the amount of water in a rainstorm.

This is especially true if you live in a rainy area like the Pacific Northwest.

3. Double Check Secondary Drain Elevation

flat roof

Another problem with installing flat roof drainage is that the secondary drain is not positioned at the correct elevation away from the primary drain.

If this is not correct, there will be permanent pooling of water around the drain area which will lead to leaks, mold, weakening of the roof structure and costly damage.

The secondary drainage should be lower than the primary and far enough away so water can flow continuously instead of pooling in the drain.

4. Protect the Drainage System

A typical flat roof drainage system is going to be made out of primarily plastic pieces. Since these plastic pieces are susceptible to breaking, they may not last as long as the roofing system.

They can also eventually wind up in the drain and clog it. As you install the flat roof drainage system you should also think about how to protect the pieces.

There are some mesh covers available for keeping debris from falling and landing on the drain itself.

5. Keep Away from Overhangs and Trees

house with flat roof

One way to keep the maintenance lower on your drainage system is to locate it away from any overhangs and trees.

While there are times when you will not be able to do this because of the elevation and positioning of the drain, you should continue to seek alternatives.

Branches, leaves, bird droppings and other things will clog up the drainage system, causing it to back up with water.