A leaking flat roof can be one of life's dreaded uh-oh moments, but the greater availability of different types of roofing materials and supplies on the market today can help make the tedious problem both short-lived and less costly.
The main issues with flat-roof repairs involve choosing the right material for the covering, or membrane, and diagnosing why the leak occurred in the first place. Many leaking roofs were too flat and initially built with inadequate structure, so they sagged in the middle, allowing rainwater to puddle and find its way through weaknesses in the covering.
Experts say a flat roof generally should have a gradient of at least 1-in-80, to allow rainwater run-off, and have a decking of marine or weather resistance plywood. If your roof is shallower than this or decked with chipboard, then it doesn’t matter what you cover it with — it will eventually leak again.
Many roofers prefer a “traditional” covering material, the current incarnation of which is reinforced torch-on felt. Properly applied, it has a life expectancy of 50 years. But newer--often less expensive--roofing products also should be considered, including EPDM (ethylene propylene diene terpolymer), an extremely durable synthetic rubber roofing membrane.
The EPDM membrane is widely used on low-slope, or flat, roofs in the United States and worldwide. Its two primary ingredients, ethylene, and propylene are derived from oil and natural gas. It is available in both black and white and sold in a broad variety of widths, ranging from 7.5 feet to fifty feet, and in two thicknesses, 45 and 60 mils. EPDM can be installed either fully adhered, mechanically attached or ballasted, with the seams of the roofing system sealed with liquid adhesives or specially formulated tape.
Other types of flat roofing include BUR or built up roof membrane, and single-ply Modified Biteman membranes. When choosing materials to replace your roof, it's important to consult a professional roofer experienced with flat roofs and replacement, or repair, materials.
Built-Up Roof (BUR) is the traditional hot-tar-and-gravel roof 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.
Modified Bitumen is a single-ply rolled roof similar to a shield, but impregnated with a mineral-based wear surface. Torch-down systems involve heating the adhesive as the material is unrolled.
Flat roofs usually come with a 10 to 20-year warranty, and the roofs can last 25 years if properly installed and maintained.