Everything You Want To Know About Ponding Water On Flat Roofs

15 May 2019
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Ponding water is a common issue on flat roofs. Few roofing systems are designed to actually hold water. As a result, one or more pools of standing water can pose some serious problems for your flat roof. Read on to learn more about how ponding water problems occur. You'll also learn what you and your roofing contractor can do to prevent future instances of ponding water.

What Causes Ponding Water?

Despite their namesake, flat roofs aren't entirely flat. Most roofs of this type feature a slight slope that directs water to a nearby interior or perimeter drainage system. Heavy rains can cause large volumes of water to temporarily pond until it eventually drains away.

Blocked drains, as well as poor drain design and placement, can lead to ponding water problems. Having too few drains can also result in backups that lead to water ponding. The roof deck itself can sag due to time and age, allowing water to collect within those depressions.

The aftermath of severe winter weather can leave pools of snowmelt to fester on your rooftop. Ice buildup can lead to the formation of ice dams, which in turn can create pockets of water trapped behind those dams.

How Can It Hurt Your Flat Roof?

Leaving ponding water to its own devices can cause multiple issues for your flat roof. The weight of the standing water alone adds undue stress on the roofing structure, leading to structural damage and premature roof failure in the future. Ponding water not only provides a habitat for mosquitos and other annoying bugs, but it also encourages algae growth, leading to clogged drains.

Pools of standing water can also intensify ultraviolet light, leading to increased UV damage in areas where ponding water is present. Vegetation can also flourish in areas where ponding water meets trapped dirt or mud. The resulting growth can wreck the roof below once the roots breach the membrane and underlying roof structure. Other problems ponding water can cause include the following:

  • Deterioration of caulking and flashing sealant
  • Water leakage at overlapping membrane seams
  • Water leakage at skylights, vent pipes, and chimneys
  • Ice formation at freezing temperatures
  • Potential flooding of roof-mounted HVAC equipment

Ponding water not only hurts your flat roof, but it can also void your roofing warranty if left unchecked. Most warranties stipulate that you not only maintain excellent drainage but also remove ponding water within 48 hours. Failure to remove the ponding water in time could result in a voided warranty.

What Are Your Preventive Options?

Prevention is always the key when dealing with ponding water issues on flat roofing systems. Removing dirt, debris, and algae from interior and perimeter drains can help resolve current water ponding and prevent new ponds from forming. Snow and ice removal are essential for preventing ponding water during the winter months. If necessary, you may need to remove pools of standing water using alternative methods, including vacuum removal, to avoid voiding your roofing warranty.

If your building features a railed rooftop, you can incorporate scuppers into the building design to allow rapid water drainage. For maximum effect, the scupper openings should always be below the level of the roof surface. You can also extend scuppers to prevent water from making contact with the sides of the building.

Low spots caused by structural sagging or other issues can be shored up through the use of roof leveling compounds. These compounds can be used to fill in depressions where water would typically pond, creating a slope suitable for effective drainage. Roof leveling compounds are a quick fix for ponding water, but they're no substitute for comprehensive roof repairs that provide more permanent results.

Contact a flat roofing service like JCB Roofing for more information.