A flat roof isn't exactly flat, since it requires a slight incline for water to drain off the surface. However, that flat roof can have issues that prevent water from leaving the surface and heading toward a downspout. Here are some reasons why your flat roof may have an issue with water drainage.

Drain Location

It's important that all drains on a flat roof are not located next to other objects that can block the path of water. This is often the case when an air conditioner is installed on a roof, but in the path where water flows to the drain. If water cannot get to a nearby drain is it going to collect on the surface, which will further weaken the roof's structure.

Drain Level

A drain should always be placed in the lowest part of a roof since that is where water is naturally going to flow. If the drain is set too high, then water news to pool on the roof in order to reach the drain. Then you're stuck with water that is trapped on the surface because the water levels are not high enough to properly drain.

Drain Strainer Clogs

Flat roof drains will have a strainer on them that is designed to prevent debris from getting into the downspout. The problem with a drain strainer is that all that debris will get caught around the strainer, which requires you to manually remove the clog so that the water can flow again.

One potential solution to a clogged strainer is that the drain holes on it are too small. It's okay for some debris to pass through if it is small enough, large debris still needs to be trapped. Try upgrading to a different strainer that will let some debris pass through and see how that helps.

Tree Debris

Sometimes you can solve a problem with debris by trimming nearby trees. If there are trees that hang over the roof and are causing more debris to fall on the surface, consider trimming those trees back to cut down on the leaves that get caught around a strainer. You'll appreciate it by making fewer trips to the roof to inspect the drains, which are due to a preventable problem around your building.

Downspout Size

You may have fixed everything previously mentioned the right way, but a narrow downspout pipe can easily lead to pooling water. The downspout needs to be big enough to allow water to flow through it freely. If it's too small, water will pool until it can slowly make its way through the downspout. 

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