Finishing a Flat Roof

While flat roofs are certainly not as common as pitched roofs, they are constructed all the time for functional and architectural reasons. When building a flat roof, the main challenge is to finish the roof in such a way that it is both waterproof and durable. The type of roofing material you use may depend on the type of flat roof that you have.

Three Types of Flat Roofs

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• Architectural Flat Roofs: Flat roofs are used on both historical and modern homes, and are sometimes chosen to visually emphasize the ground level of a structure and its surrounding environment. For example, a pueblo revival home might have a flat roof finished with tile and adobe, reminiscent of the ancient Indian pueblo villages of the American Southwest. Flat roofs are common on many modern looking homes, as well--architects like Ludwig Mies van der Rohe and Frank Lloyd Wright used flat roofs on some of their most famous designs. If a flat roof is not going to be seen, it can be finished with layers of roofing felt and tar or a waterproof rubber membrane such as EPDM.
• Flat Roofs for Mechanical Reasons: Usually constructed in conjunction with a pitched roof, there are times when a small, flat roof is needed to house mechanical equipment for a home or multi-family building. Oftentimes, these flat roofs are surrounded by small walls called parapets, which are used to hide unsightly HVAC equipment such as air conditioning units. These roofs must be durable because they get walked on by contractors who work on the mechanical equipment, and therefore rubber membranes may not be the best choice because they can be torn or damaged underfoot. A better choice may be rolled asphalt roofing.
• Functional Flat Roofs: A functional flat roof might be constructed to support a rooftop garden or a second-story balcony. These flat roofs usually incorporate a waterproof layer, such as a rubber EPDM membrane, underneath a finished surface, like roof tile or wood decking. The challenge when constructing a functional flat roof is that rainwater must be collected and diverted off the roof by way of a slight slope, but the finished surface must remain dry and level for people using the roof top. When the finished surface is wood or tile, the roof needs scuppers and a drainage system to collect and disperse any water that collects underneath the wood decking or tile roof.