What is the risk associated with increasing ponding depth?

• A. Increased load leading to potential instability.
• B. Reduced load on the roof.
• C. No effect on structural risk.
• D. Improved drainage efficiency.

Answer: (A)

Water that ponds on a roof adds weight to the structure, and the deeper the pond, the more load the roof must carry. Water weighs about 62.4 pounds per cubic foot, so ponding depth translates directly into increased dead load and greater hydrostatic pressure on the roof deck, membrane, and supports. This extra load can push the roof past its design capacity, causing more deflection, membrane stress or seams failure, and in extreme cases, structural instability or failure. In short, deeper ponding raises risk by increasing the load the roof must bear.

The other ideas don’t fit because deeper ponding does not reduce load, it increases it, and ponding does not improve drainage; it actually reflects inadequate drainage and can worsen performance and durability.