How to Prevent Pooling Water on a Flat Roof

Inspect the roof at least three times a year for damage. Inspect more often if nearby trees cause a buildup of leaves and debris in the drainage system. Look for standing water, low or indented areas that contain debris, mushy sections that look like blisters, holes, a pattern of cracks in the roof surface and gaps in the flashing. Also look for damage to the membrane if the roof has one.

Repair any problems found during the inspection. Fill in and resurface indented areas, apply new roofing tar to the entire roof if cracking is a problem and repair damage to the drainage system.

Check the roof after heavy rains and snowfalls, especially during thaws when snow or ice can block drains and cause pooling of water.

Clean out the roof drainage system -- including pipes, gutters and downspouts -- and seal, repair or replace the flashing around the roof. Flashing, which is usually made of aluminum or steel, is installed at the joints between roofs and walls and around chimneys, pipes and other structural elements through which water can seep into the house if the flashing is defective.

Repitch the roof to create an angled surface, or install tapered insulation to create a slight slope on the roof. Both improvements will prevent water from pooling in one place on the roof.