What clues might indicate prior ponding on a roof despite no rain at the time of inspection?

The presence of dirt, algae, and vegetation is a significant indicator of prior ponding on a roof. When water collects and remains stagnant on the surface of a roof, it creates an environment conducive to the growth of algae and the accumulation of dirt and debris. Over time, this standing water not only facilitates the growth of biological materials but can also lead to discoloration and staining of roofing materials.

This presence is particularly telling, especially if there has been no recent rain. It suggests that water stood in these areas long enough to support such growth, indicating that ponding may have occurred in the past. Other factors, such as visible wear and tear on shingles, unusual roof shapes, or flashing damage, may point to various roofing issues but do not specifically signify prior ponding as clearly as the presence of algae and vegetation does.