The best choices for a flat roof are roofing materials that are truly waterproof: metal and built-up roofing. You can also use roll roofing, but is generally just used for shallow sloped roofs, not flat.
The first choice for a flat roof today is one made of aluminum. Older metal roofs, however, may be terne—a tin-steel allow—or even copper. Modern-day styles include corrugated or ribbed panels and shingle strips. Aluminum roofs are a good, non-combustible heat reflector. Some, but not all types are suitable on flat roofs.
Maintenance of an aluminum roof is perhaps its best selling feature. Aluminum roofs are very easily maintained except when the aluminum comes in contact with any other metal, which results in electrolytic action, causing deterioration. Be very careful with other metals of the roofing, even an antenna, as this is the largest downfall of metal roofs.
If you have a terne or copper roof, repairs are easily performed with simple soldering skills. To solder terne you use rosin flux and then coat it with red-lead primer and paint to match the rest of your roof. Terned stainless steel does not need priming or painting. If your roof is made of copper, use acid flux for soldering. Copper roofing does not require priming or painting. If your roof is made of aluminum, you cannot solder it. Seal any cracks with aluminized caulk and patch bigger areas of damage with fiber glass. If the aluminum has been painted, it may need periodic painting.
The life span of an aluminum roof is up there with other roofing types lasting up to 35 years. If your roof is made of copper or terne the life span is even longer as these metals are even more durable than aluminum.
Unlike shingles, shakes, slate, and tiles, built-up roofs must be absolutely waterproof, a quality that makes build-up roofs a good candidate for flat roof situations. A built-up roof is usually fabricated on the job by laminating layers of felt with asphalt or coal tar, then topping with gravel.
Maintenance problems related to built-up roofs usually stem from improper application at the beginning. Unfortunately, leaks from a poor job can plague you through the life of the roof. Fortunately, repairs are relatively easy. When repairing you use roofing cement for small cracks and the same materials used for the original roof to repair larger areas of damage.
The life span of a built-up roof is not very long, from 5 to 20 years. Generally, the more layers, the longer life you can expect.
Roll Roofing is similar to asphalt shingles, but comes in wide strips that are lapped horizontally across the roof’s surface. It is most often applied with lightweight, single-layer installations, which fail frequently. However, repairs are very easy. Roll roofing, which has a life span of 5 to 15 years, is really intended for a shallow slope, and should therefore only be considered for a flat roof if metal and built-up roofing are not an option.