Homeowners understand that a house is an investment. The same goes for building owners. They understand the importance of protecting those investments. However, such investments are vulnerable to the seemingly innocuous pooling of water known as ponding water. Ponding water can compromise your roof system, void your roof warranty, and lower your property value, so it is important to understand the harmful effects of ponding water so you can take preventative steps to protect your roof.
Negative Effects Of Ponding Water
While most flat roof materials are built to withstand water, over time standing water deteriorates the roof membrane and diminishes its resilience.
Water is heavy! Water left standing on a roof 48 hours after rain puts stress on the roof system and can cause permanent structural damage.
Ultraviolet (UV) Radiation Damage
Water acts as a magnifying glass and intensifies sunlight, increasing UV ray damage to the roof membrane.
Ponding water attracts mold, insects, and slip hazards – another reason why water left standing 48 hours after a rain can void your roof warranty.
For more, see: The Effects Of Ponding Water On A Flat Roof
Common Causes of Ponding Water
A small amount of standing water on a roof after rain is completely is normal and acceptable. However, while most commonly used flat roofing materials (e.g. Asphalt, EPDM, Modified Bitumen, PVC, TPO, etc.) are built to withstand harsh weathering conditions, they are not intended to hold water for long periods of time. The longer water sits on a roof, the more likely it is to cause damage to the roof membrane, so it is crucial to identify the cause of ponding water as quick as possible. Some common causes are:
Ponding water accumulates in areas with depressed roof insulation. A roof’s insulation can be crushed from:
- Heavy equipment (e.g. HVAC units)
- Fix: Inspect areas surrounding heavy equipment. Look for dried up water spots. In some cases, deck reinforcement or tapered insulation may be necessary while in others, crickets and/or a roof leveling compound like GreenSlope can be used to slope the roof and direct water to a drain.
- Structural impairments from previous incidents of water ponding
- Fix: In many cases, a leveling material can be used in to fill in the low areas and bring the roof back to it’s original slope.
- Leaks which cause the wet insulation to become damaged and ineffective over time
- Fix: Patch the leak and replace the insulation. Taper the insulation to slope towards desired drainage areas.
As buildings settle into their foundation, over time less-supported areas will become displaced causing their roofs to sag, allowing ponding water to accumulate. This is natural and not necessarily a problem with the initial design or installation.
- Fix: When you suspect the ponding is caused by a structural issue, consult a local roofing expert, as these can be expensive fixes. Do-it-yourself roof leveling compounds may or may not be enough to eradicate the problem long-term, depending on the size and scope of the ponding area. For many cases, an expert may recommend a combination of roof filler and tapered insulation, while a re-roof may be recommended for more extreme cases.
Skylights & Rooftop Units
Large rooftop units (RTUs) and skylights also tend to collect water. Most of these units have a tapered solution in place called crickets to prevent infiltration and direct water towards drains.
- Fix: If these units still collect ponding water, a roof leveling compound, such as GreenSlope can be used to better direct water toward desired drainage areas.
Improperly Installed Drains And Scuppers
Flat roof systems are designed to enable water to flow off through drains and scuppers. These should be installed at low points where the roof is sloped to direct water or where water naturally flows. However, improperly installed drains and scuppers can exacerbate the problem of water ponding. For example, when a drain is installed too close to a column, the less-supported surrounding areas tend to sink in and collect water. Similarly, if scuppers are installed near an edge where the insulation is not properly tapered i.e. the edge is higher than the surrounding areas, water will pool in these lower areas and the scupper therefore becomes ineffective.
Fix: To identify low areas on a dry, flat rooftop, on a hot day, take a hose and spray it across the roof for a while. Let it sit for an hour or two before returning to inspect the results. You should be able to pinpoint larger ponding areas where water hasn’t evaporated yet. These might good areas to install a new inner drain or lay down a roof leveling compound to redirect water to a nearby one. Filler materials like GreenSlope can also be used to slope areas near scuppers to bring the surface level up and allow water to flow more freely off the roof to a gutter or downspout.
The roof surface is below the scupper, causing water to pool instead of flowing freely off the roof via the downspout.
The GreenSlope roof leveling compound is applied to the roof surface to bring it back to it’s intended slope, facilitating proper flat roof water drainage.
Whether you own a home or an industrial building, remember that it is an investment. And the efficacy of your roof can dramatically impact the value of that investment. Over time, ponding water can devastate an otherwise well-maintained building and insurers are increasingly refusing to cover damage from ponding water. Understanding the common causes of ponding water and taking preventative steps to protect your roof are the best ways to protect your investment.