-Extensive pooling of water: The biggest issue with flat roofs is pooling. If your roof regularly develops pools of water you should consider having it replaced.
-Large rips and tears in the material and/or seams: Flat roofs may eventually develop tears and holes in the roofing material. This issue is particularly likely to crop up along seams in the roofing. This is where two pieces of material were joined together.
-Roofing material that does not easily show damage: It is simple to find the holes in some types of roofing material such as membranes made from various materials. Other types of roofing material–such as a tar and gravel roof–are more challenging. Even an experienced contractor may have a hard time finding and repairing holes. If your roof is composed of a troublesome material that does not allow contractors to easily locate leaks, you may want to consider replacing it with a different type of roofing.