The major problem with flat roofs is that they are flat! This means there is often an opportunity for water and debris to collect. All flat roofs are designed with some slanting of their surface to allow water to flow towards gutters or roof drains. When this is interrupted the result is ponding, or puddles of water that remain on the surface indefinitely. Constant saturation from ponding will lead to a steady deterioration of the roof surface followed by water penetration. And the worse it gets, the worse it gets, to the point of major and expensive roof damage!
The answer to a weather-tight flat roof with minimum expense is constant inspection and maintenance. Any reputable building maintenance company should inspect the flat roofs of their clients no less than twice a year. Yes, that usually means hauling out a 25-foot or higher ladder for most industrial buildings, but that is a lot cheaper than major roof repair.
What should a roof inspector look for in the inspection? First, the roof must be free of ponding and debris. Gutters or roof drains must also be free of debris and free-flowing. Next, look for blistering, splitting, alligatoring and felt movement. Blistering is a result of air being trapped between the roof layers. A hot roof heats up the air in the blister causing a break, thus allowing water to penetrate and ultimately leak into the building. Splitting and alligatoring are cracks in the roof membrane that are caused by a freezing and thawing cycle, heat, stress, or simply a poor installation. Finally, inspect the flashing, which is the metal detail that joins a flat roof to a masonry wall. Properly executed, flashing allows the component parts of a roof to move while remaining watertight.
Any problems found should be promptly addressed. Gutters or roof drains need to cleaned, and if necessary replaced. Blisters will have to be cut out and replaced. Flashing may need to be repaired or replaced. Splitting and alligatoring will probably be cured with a new application of roofing tar. You may want to consider coating your flat roof with reflective aluminum paint, if that has not already been done. The reflective paint significantly reduces the heat load on the roof, and also lessens the impact of the sun on the deterioration of the roof materials.
Even with the best of maintenance programs, no roof lasts indefinitely. Depending on your roof type, you will need to plan on replacing your roof every 10-20 years. Obviously, more expensive roofs are expected to last longer. Just as you replace the filters in your heating system on a regular basis, so must you invest in annual roof maintenance. The key is to nip the problem early and inexpensively. This is the best way to maintain both your roof and your sanity!