How do you know what kind of flat roof is right for your building?
Built-Up Roof (BUR) The traditional hot-tar-and-gravel roof is built from three or more plies of waterproof material alternated with hot tar and ballasted by a layer of smooth river stone. Once made of tar paper, these types of roofs gradually are using more-advanced materials such as fiberglass membranes.
Pros: Gravel is an excellent fire retardant. Attractive for windows and decks that overlook the roof. It's the cheapest of the four roof varieties.
Cons: Very heavy. Joists sometimes have to be strengthened. Smelly and messy to install. Installation's not recommended for occupied homes. It's not a DIY installation job, and it is hard to find the source of leaks. Gravel can clog gutters and scuppers.
Modified Bitumen A single-ply rolled roof similar to ice-and-water shield, but impregnated with a mineral-based wear surface. Torch-down systems involve heating the adhesive as the material is unrolled. Newer peel-and-stick systems are safer and easier.
Pros: Peel-and-stick material can be installed by homeowners. Its light-colored mineral surface reflects heat and cuts energy bills. Its price is in the middle of the pack.
Cons: Torch-down application is a fire hazard, and not recommended for occupied buildings. It's not as scuff- or tear-resistant as rubber-membrane roofs (see the next item).
Rubber Membrane EPDM (short for ethylene propylene diene monomer) is a true rubber. The durable material resembles an inner tube, but it's engineered to resist damage from sunlight. EPDM can be mechanically anchored with fasteners, ballasted with stone, or glued.
Pros: Homeowner-friendly installation. The material's relatively light yet highly resistant to scuffs and tears. Leaks are easy to patch.
Cons: The standard black material absorbs heat, and light-colored coatings (recommended in warm climates) add 30% or more to the cost. Even the black version, though, costs more than BUR or modified bitumen. It's also more vulnerable to punctures than other choices.