A flat roof generally requires more maintenance than a traditional pitched roof. These are more commonly seen on commercial buildings, but occasionally a homeowner will have a flat roof. Shingling these types of roofing systems is usually not a good idea. Here's why.
Installing flat roof shingles is a process that is complicated, and should only be done by professionals. Most cities require a slight pitch for a shingled roof. Adding a pitch to a flat roof requires construction. On top of that, many roofers prefer to use a roll out roofing system. These require more preparation and extreme heat to apply. In most cases, a torch that is heated to over 2000 degrees is required. This poses many risks.
A flat roof can remain leak-free for around 7 years. Adding shingles can actually lessen this time. When shingles are installed, even when done properly, water can become trapped under the shingle. On a pitched roof, the water won't stay trapped. However, on a flat roof, there is no place for the water to go. This can cause the roof to become weak, and develop leaks more quickly.