Flat roofs are also called low sloped roofs, as there is usually a small slope to it to aid in the water shedding process and to keep areas of the roof from pooling up with water. However, even with the low slopes these roofs have, it is not ideal to have a flat roof in areas that receive heavy rainfall, and special care must be taken in order to ensure the roof has a good water drainage system. If water is left pooled on a flat roof for too long there is a good chance of roof failure. The upside to a flat roof is its economical construction, as less material is required and is thus less expensive, however flat roofs must be re-roofed more often than typical pitched roofs.
There are several different materials that often cover a flat roof. One type of flat roof is the BUR, or built up roofing. This is when the roof is made up of layers of felt, various water proofing materials such as asphalt or tar, and is topped with gravel or other mineral.
A Single-Ply flat roof is a popular form of flat roof, as it uses waterproof membranes to cover the entire roof, with overlaps being sealed by liquid adhesives. This is more expensive to install, but is generally worth it as it has less problems with leaking.
Spray on materials can also be used on flat roofs. One newer product, SPF or Sprayed Polyurethane Foam is a product that is sprayed onto the roof as liquid, and it forms a seamless structure for the roof. The foam gives the structure a higher R-value as it helps insulate the building. This can help save in heating and cooling costs. This method hasn't been around for long, so make sure you're well informed of this product before using it.
FLAT ROOF TYPE ILLUSTRATIONS