One of the more common issues suffered by a commercial roof is the problem of ponding water. Ponding is when puddles of water collect on your flat roof and don't drain off within a day or less, with the result that you have standing water that remains on the roof for some time after rain or snow melt. If you don't spend a lot of time on the roof, you may be unaware that ponding is occurring. The following are a few signs that can clue you in to this problem.
When water collects, particularly in warmer weather, vegetation is able to grow. Most often, what you will notice are green to blackish-green stains that indicate algae growth, particularly on roofs with lots of sun exposure. In shaded areas of the roof, you may see moss growth on the roof material. In some cases, there may be actual weeds and plants taking root, especially if there is dirt and debris on the roof for these plants to root in. Vegetation indicates that moisture tends to persist on the roof long after rain.
High Bird Presence
Birds will perch and sometimes nest on just about any building that doesn't have anti-bird devices, but your roof will seem to host a lot more birds than neighboring buildings if it also features a water source on top. Like any animal, birds prefer to roost and nest near a water source, which roof ponding may provide. If you have noticed more birds on your roof or if your roof seems to be littered with bird droppings and nest materials, then ponding may be an issue.
Water that dries slowly tends to stain the roof. You can usually find these darker water stains most easily on light-colored roofs, but they can also be visible on darker roofs. Water stains are often roughly circular or oval in shape, as they indicate that a pool collected in a low area of the roof. Sometimes, if the ponding water is causing a leak, you may find a similar stain on the interior ceiling, directly beneath the ponding stain up on the roof.
Every flat roof is equipped with drains, typically around the perimeter and at least one in the center. A quick inspection can tell you if these drains are blocked with debris on the surface grates. Drains can also be blocked internally, so try pouring water down each drain to verify that it is coming out the other end. If a drain is blocked, then chances are there has been some ponding occurring on the roof.
Contact a commercial roofing contractor for more help.