How To Prevent Ponding Damage On A Flat Roof

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Shingle Me This: A Roof Blog Roofers have a tough job. They work at heights, carrying heavy shingles and nailing them to the roof's surface. In addition to working hard, roofers are also very knowledgeable. They can recommend the best roofing material to fit your budget and preferences, and they can make repairs, as needed, to ensure your roof continues to keep your home safe. There's a lot to learn about roofing. We are not professionals, but we consider ourselves to be well-informed, and we share the information we know on this website. As you read, you will learn more about roofing as a profession, and you may also pick up some roofing tips you can use on your own home.



A major concern for business owners is ponding on a flat roof. This common problem typically affects commercial buildings with large, flat roof expanses. The effects of ponding can be severe -- leaks, damage to rooftop HVAC systems, premature roof replacement, and roof collapse are all possible consequences. The following guide can help you avoid ponding problems on your roof.

Insufficient Drains

Flat roofs depend upon ample drainage to prevent water from collecting on top. Smaller roofs may only have perimeter drains, which may drain down gutter systems attached to the side of the building. Larger roofs or buildings with more involved footprints may also have central drains on the interior of the roof. These drains enter an interior drain pipe that usually empties into the municipal stormwater system. A roofer can assess your roof to determine if there are sufficient drains and arrange for the installation of any additional drains that are needed.

Drain Blockages

A common reason for ponding is that although there are plenty of drains, they have become blocked. Bird nesting materials, dead leaves, and other detritus can get into drains and drain pipes and create a blockage. Clearing the drains will fix the problem, but it is necessary to take steps to prevent blockages in the future. Screens over drain openings keep birds and some debris out. It may also be necessary to install bird prevention devices, such as spikes, to keep them away from drains. Periodic roof cleanings will also help prevent future blockages.

Slope Issues

Flat roofs aren't really flat. They actually slope slightly towards the drains. For example, a roof with perimeter drains will be slightly higher in the center so that the rest of the roof slopes toward the drains at the edges of the roof. Those with central drains will slope inward, toward the center. The slope may vary as one walks across the roof in response to the location of the nearest drain. If this slope isn't sufficient, a roofer will need to build up sections of the roof to fix the issue.


Damages can lead to ponding on roofs with asphalt or tar covering. Just like with an asphalt road, these roofs can develop depressions or potholes that collect water. Further, the depressions increase the chances of a leak. Fortunately, damages such as depressions and holes can often be repaired, so a new roof installation may not be necessary.

Contact a commercial roofer for more assistance.

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