Flat roofing is a fixture in both commercial and residential construction. Often found atop multistory buildings, flat roofs are horizontal and level, instead of sloped. Flat roofs are popular primarily because they are one of the most inexpensive types of roofing. They are also convenient and accessible in a way that sloped roofs are not. The space on a flat roof can be used for things like rooftop gardens and solar panels. Since flat roofs have a tendency to trap water, they are typically covered with a waterproof membrane, which is vital to the structural integrity of the building.