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here are two ways water can leave a roof — positive drainage or evaporation. When neither can occur quickly enough, the result is ponding water. Ponding water is defined as any water remaining on a roof 48 hours after a rain. Any building with a flat roof has the potential for ponding water, but it also commonly occurs on low-slope commercial roofs. It’s typically the result of poor building or roof design and/or poor drainage, and it can be widespread across the roof or in small areas of a roof section. Pockets of ponding water can also form on the roof after a building or roof surface settles in time.
In addition, penetrations on a roof’s surface can lead to ponding water because they make it more difficult to maintain positive drainage after a rain or snow event. Therefore, the more roof penetrations a roof has, the more likely it is to have ponding water.
Ponding Water Problems
Ponding water can cause significant damage to your roof and building as well as quicken deterioration of the membrane. In normal conditions, roof membranes can deteriorate at a rate of 1 to 1.5 mils per year, but those under ponding water conditions, that deterioration happens much faster. This leads to earlier exposure of the reinforcement scrim ,which usually results in roof failure sooner rather than later.
Ponding water can make roof membranes brittle, which weakens the system and reduces waterproofing. For those climates with higher UV rays, ponding water is extra troublesome because it essentially acts as a magnifying glass for the sun.
In addition, ponding water sitting on a roof can sneak under the membrane to the insulation. Wet insulation can cause structural damage, compromised indoor air quality, mold, and more.
Other issues that can result from ponding water include:
- Vegetation. Weeds, grasses, algae and other vegetation can begin to form and grow from excess moisture on the roof. This can lead to debris on the roof, clogs in the drains and long-term damage.
- Insects. Water attracts insects like mosquitos, cockroaches, carpenter ants and more. When these insects get inside the building, your issues with them and costs to exterminate them both increase.
- Birds. Water also attracts birds and with them comes unwanted noise, excrement and debris.
- Discoloration. Ponding water can discolor a roof over time, particularly a white roof. This can decrease a roof’s performance and make any visible roof areas less attractive.
- Ice Damage. Ice formations from ponding water may develop in winter weather and cause further physical damage to the roof membrane.
Fixing Ponding Water
If you notice ponding water, it’s most likely already causing damage so fixing it quickly is paramount. Depending on your roof type and building design, there are numerous ways to resolve ponding water:
- Drainage Systems. Adding more drains, lowering areas around the drains or gutter areas and/or installing saddles in between the drains will help prevent back-ups.
- Tapering. Tapering involves adding 1/8 inch or 1/4 inch per foot of tapered roof insulation to create slope and allow water to move toward new or existing drains. When tapering to existing drains, ensure the drains can handle the additional water flow. Most buildings are built with very little slope in the roofing deck. If your facility has multiple HVAC or other rooftop units, tapering may not be practical because penetrations can make it expensive.
- Timing. Address ponding water areas as a first step when you’re considering a re-roof or restoration. Adding reinforced layers of polyester or coating in ponding water areas will help to protect the original roof membrane underneath.
The next time it rains, wait a few days and then take a look at your roof. If you notice any spots of ponding water, make note of where they are and how much water there is – even take photos, if possible.
Simon Roofing understands the challenges ponding water creates and has proven solutions to help remediate it and avoid it. Between our inspection team, our in-house design team and our trained technicians, we are able to properly identify ponding water and its resulting damage — and determine the best way to resolve it quickly and correctly.
