In contrast to the sloped form of a roof, a flat roof is horizontal or nearly horizontal. Materials that cover flat roofs typically allow the water to run off freely from a very slight inclination. Traditionally flat roofs would use a tar and gravel based surface which, as long as there was no pooling of water, was sufficient to prevent penetration. However, these surfaces would tend to fail in colder climates, where ice dams and the like could block the flow of water. Similarly, they tend to be sensitive to sagging of the roof reversing the subtle grading of the surface.
Modern flat roofs tend to use a continuous membrane covering which can better resist pools of standing water. These membranes are applied as a continuous sheet where possible, though sealants and adhesives are available to allow for bonding multiple sheets and dealing with structures penetrating the roof surface. Other flat roof options include elastomerics and self-adhered flat roof systems.
Flat roofs tend to be sensitive to human traffic. Anything which produces a crack or puncture in the surface can quite readily lead to leaks. In other words, this sort of roof has a major weakness to failure from subsequent work done on the roof – such as upgrading building HVAC systems and so forth. It is thus not generally advisable to use a flat roof as a living area unless steps are taken to protect the roofing membrane from those using the area, for example, by building a wooden deck over the surface or using paving stones or similar materials to protect the roof membrane. It is not advisable in general to have living areas directly under such a roof either, due to the high likelihood of eventual leakage.
One of the more interesting (re)emerging methods of protecting the roofing membrane is to use a layer of topsoil and grasses. Care should be taken not to plant anything the roots of which will penetrate the membrane surface. The green roof interestingly enough, tends to trap moisture on the roof, but keeps it up in the soil and plants, rather than having it pool down on the membrane surface.
There are many different types of roofing available for your home. Please click the following links to learn more