Ponding Water

What is ponding water?


Water remaining on your roof for more than 48 hours after a rain ends is ponding water by definition of the National Roofing Contractors Association. This remaining water is one of the most damaging things effecting the life cycle of a flat roof. Even when code requirements are met, some slope is lost due to components suspended from the roofing joints and roof top equipment such as HVAC units. Ponded water can invade the roofing system through any imperfection, no matter how slight. Imperfections like alligatoring (or checking), splits, cracks, fishmouths, bare felts, or an unsealed lap or seam are all risk factors. If the moisture reaches the insulation this can result in rotted organic fibers, weak binders, and reduction of thermal resistance.





Why is ponding water so detrimental to my flat or low-slope roof?

Ponding water can deteriorate the roofing surface. In some instances, organic matter thrives in the ponding water using the roofing adhesive as a food source. This is especially detrimental if the ponding water occurs at a natural weak point of a roofing system, for example at a penetration or a seam. The organic matter can develop into a fungi or a plant. If plant growth occurs, the roots can penetrate the the membrane, reaching into the insulation. Once the plant dies, a large opening is left in the roofing system. Once moisture is trapped underneath the membrane, it will expand and contract as it freezes and thaws. The expansion can cause splits and cracks to increase in size, allowing more moisture to penetrate the roofing system. This freeze-thaw cycle can lead to ice formations. Along with the expansion and contraction, movement may occur. As these formations travel underneath the membrane, enough friction can be generated to cause considerable physical damage to the membrane. Even small amounts of moisture trapped underneath the membrane can reduce the insulation's thermal efficiency and damage the roof deck, insulation, membrane, and the interior and contents of the building. Most importantly, ponding water can increase the load on the roofing deck, and in some cases compromise the structural integrity. Given the approximate wait of ponding water is five (5) pounds per inch per square foot of roofing surface, a small 14x15 square foot area of a roof with two (2) inches of ponding water can add just over an additional ton (2,100 lbs) of weight to the roofing deck. 14x15 = 210 square feet x 10 (2 inches x 5 lbs)= 2,100 lbs. A 10x10 square foot section with one (1) inch of ponding water adds an additional 500lbs. Proper drainage is very important.


Does my warranty cover damage from ponding water?


Probably not. The existence of ponding water will void warranties from most roofing material manufacturers.


How can LaFerney Commercial Roofing help?


LaFerney Commercial Roofing offers single-ply membrane roofing systems with 15 and 20 year No Dollar Limit warranties unaffected by ponding water. In addition the warranty provides coverage for consequential damages to protect the contents of your building*. This same system features factory heat-welded seams and pre-fabricated boots to flash all penetrations, reducing the risk of leaks by 85%. LaFerney Commercial Roofing can also evaluate and adjust drainage issues. Other options are available when dealing with ponding water issues. Contact LaFerney Commercial Roofing for a free roof evaluation, solution options, warranty details, and a free estimate. (800) 633-3119


LaFerney Commercial Roofing is now proudly serving the Knoxville, TN area for flat roof repair, flat roof metal retro-fits, and office building roof repair.
*Please click here to view sample warranties or contact a sales consultant at 800-633-3119.

Ponding Water is one of the most detrimental events to occur on a roof.