If your building has a flat or low-sloped roof, there are a few potential issues that you should be aware of. One common problem with these roofs is ponding water. Ponding water is usually defined as water that has not drained from your roof within forty-eight hours after collecting.
This water may not cause immediate damage, but over time if water does not drain well, it could cause some major problems to your roof. Water weighs about five pounds per inch of depth, per square foot of roof surface. So one inch of ponding in an area of only 10 feet x 10 feet – 100 total square feet – would add 500 pounds of weight to that area – potentially compromising the structural integrity of the building.
In addition to potential structural problems if water is not removed, algae and bacteria can begin to grow and deteriorate the roof surface. Plus, standing water can contribute to the breakdown of the roof coating, because it intensifies sunlight. The water could also begin to leak into the building if seams between membrane sections have lost their integrity.
Ponding water is usually caused by poor drainage on your roof, due to any number of factors: faulty installation, extreme weather conditions, compressed insulation (from foot traffic, perhaps) or structural sagging. Whatever the case, this water needs to be removed from the roof immediately and a drainage remedy needs to be implemented.
One solution may be as easy as ensuring that drains, gutters and downspouts are clear of debris and running freely. More extensive fixes (probably requiring the involvement of a commercial roofing contractor) may include adjusting the roof slope with crickets or tapered insulation to eliminate ponding water by providing positive drainage.
If you’re considering a new roof keep in mind that most manufacturers don’t cover ponding water in their warranties; however, some manufacturers have no warranty exclusions for ponding water.