Flat Roofs
While not really flat or horizontal, a flat roof is usually nearly horizontal and is made with materials that allow water to run off freely from a very slight inclination.
Unlike traditional flat roofs that were made with tar and gravel, 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. More expensive flat roofs are made with sealed metal roofs, utilizing copper or tin, which are soldered to interlock the systems of metal panels of the roof.
While a few of the famous Modernist architects, like Le Corbusier, viewed flat roofs as a living area, flat roofs cannot be used that way until the roofing membrane is properly protected. One way to accomplish this is to build a deck or use paving stones to protect the roof membrane.
An interesting method to protect the roofing membrane is a Green Roof, which uses a layer of topsoil and grasses. However, it is important not to plant anything that has roots that would penetrate the roof membrane.
The most common type of flat roof is the asphalt built up roof (BUR), made of multiple layers of reinforcing plies and asphalt. The reflectivity of built up roofs depend on the surfacing material used. Gravel is the most common and they are referred to as tar and gravel roofs. But the degradation by UV-rays of the asphalt as well as serious air pollution are problems and other substances are becoming more popular.
A flat roof must be maintained properly to last a typical 10 year life expectancy.
Interestingly, the old fashioned BUR roofs that are properly maintained have lasted over 100 years. Maintenance includes removal of ponding water with a siphon that runs regularly. All roofs should be inspected semi-annually and after major storms.
Hip Roofs / Pyramid Hip Roof / Cross Hipped / Mansard Roof / Gable Roofs / Cross Gabled Roofs / Saltbox Roofs / Flat Roofs / Gambrel Roofs