Pooling is one of the most common problems on a flat roof. This happens when the roof does not drain rainwater as it should. The weight of water, and other soaked debris that has collected, places excess stress on joints and seals. A roof that either has pooling that covers a large area, or is more than 20mm deep might at least need a professional assessment.
Visible signs of potential drainage problems on a flat roof, other than the obvious presence of pools of water, include the growth of mosses and other plants and watermarks that indicate where water has previously collected.
Flat roofs with pooling problems don’t necessarily need to be replaced as patch repairs can sometimes be made.