What do water stains on a flat roof indicate?

Water stains on a flat roof typically indicate previous pooling. This situation arises when water accumulates in areas of the roof that do not drain properly. Over time, the pooling can lead to moisture being retained in the roofing materials, which then results in visible stains on the surface of the roof. These stains serve as evidence of past water accumulation that may have occurred due to insufficient drainage or an improper slope.

While moisture from rain can contribute to water stains, it does not specifically indicate the long-term effects of standing water as previous pooling does. Similarly, condensation issues can occur on roofs, but they are usually associated with internal humidity and ventilation problems rather than indicating the presence of water stains specifically caused by standing water. Underlying structural damage is a more significant concern, but the water stains themselves do not directly indicate current structural issues; they point to previous conditions that could lead to such problems if not addressed. Thus, recognizing previous pooling as the cause helps in assessing the overall health and maintenance needs of the flat roof.