How To Repair Commercial Flat Roof Ponding

by | Jan 16, 2024 | Flat Roof Repairs, Tips and Techniques

Commercial flat roof ponding is a common occurrence that can potentially lead to roof membrane and structural damage. This post provides four effective solutions to flat roof ponding problems considering the unique needs of commercial property managers and flat roof building owners, especially in the US northeast and Philadelphia area.

But first, you need to determine what is causing the ponding to occur in the first place. Identifying the root cause of the problem will help guide your repair strategy.

Determine Root Cause

Check for blocked drainage, improper slope, or damaged roofing materials to help determine what might be causing your flat roof to leak.

Some puddles can be minor (relatively small and shallow) or major (large and deep).You will want to have major ponding issues repaired quickly and professionally because they can wear your roof membrane much faster due to seasonal freeze thaw cycles. More importantly, the water intensifies the UV radiation which translates into additional wear on your membrane.

Then we recommend four basic methods to fixing ponding water. The preferred method will depend on the root cause of the ponding, the slope of your roof, plumbing proximity, and in two instances, the interior of your building.

1. Clear Drains and Gutters

Clogged Drains on Commercial Flat Roof |
This is a straightforward first step.

Ponding is often exacerbated by clogged drains and gutters. Clear any debris or obstructions to ensure proper water flow. This step alone can sometimes significantly alleviate ponding issues.

2. Add a Drain

This can be an effective solution for roofs with some slope. Its feasibility depends on your building interior and plumbing proximity.

If the interior of your building permits it, consider adding a drain in the center of the puddle. This is usually the best course of action if your roof is too flat to enable water being directed to drains and gutters.

Commercial Flat Roof Tie-In to Existing Plumbing |
Ponding water naturally creates a basin. Adding a drain to the basin gives the water a way to escape.
How do you know if your building can sustain a new drain? The answer to that question has to do with plumbing. If the building is a wide-open warehouse and the new drain is reasonably close to existing plumbing, you might have the option to create an easy tie-in to the existing plumbing. If your building is completely finished and the plumbing is impossible to access without demolition, then this might not be the best solution and you should keep reading.

3. Raise the Roof Level

This next method utilizes the roof’s existing slope, drains, and scuppers to direct water away from the rooftop. You must have some slope on your roof for this method to work.

Example Commercial Flat Roof Cricket |

Generally the best way to redirect the water is to build a cricket. A cricket is a diamond or triangle-shaped elevation in the roof that redirects water towards a drain. A cricket works with the existing slope of the roof so that as the water runs down in a straight line, it hits the cricket, and is redirected laterally towards a drain or scupper.

If your roof is dead flat and you have areas of ponding, raising puddles up generally won’t help. All it will do is move the water from one spot to the next lowest one. Because the roof has no slope, the water cannot be directed toward a drain or scupper. Raising the level of the ponding area will accomplish nothing.

4. Lower the Roof Level

This method is best for buildings with restricted plumbing options. Costs and structural considerations need evaluation.

If the interior of the building is too closed off to run new plumbing, then lowering the roof from up top can be a solution. One way to do this is to build a sump around an existing drain.

Commercial Flat Roof Drain | getflatroofing
Sumps are like the inversion of a cricket where the triangles direct the water down and towards the drain.
Drain Has Been Lowered to Create a Flat Roof Sump

Another option is to build channels in the roof to direct the water to a drain or a scupper box. If the roof is built up with a good amount of insulation, you may be able to cut a narrow channel into that and direct the water from the puddle to a drain or scupper.


So there you have it.

Identifying the best solution to your ponding problem is a matter of evaluating the specific circumstances around your rooftop and the relative feasibility and cost of each option. If the roof is quite aged already, perhaps the best option is to not bother with any of the above and, instead, put your repair money towards a roof replacement. Working with an experienced roofing professional you trust, you should be able to address any ponding issues.

Expert Advice

Whether you’re a beginner, need advanced information about flat roofing topics, or a refresher,  this is where you can learn everything you need to know about commercial and industrial flat roofing.

Contact us for more information or pricing.




Jared Van Vranken is Vice President and lead estimator at Flat Roof Solutions in Malvern, PA. Jared has directed the installation, repair, recovery, and replacement of commercial flat roofs for more than a decade at Flat Roof Solutions. He guides clients in selecting the best roofing materials for their needs and budget.

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