Rubber Membrane Roof Options

EPDM

• A single ply membrane, EPDM the most commonly used roofing material for low slope roofs, those with a rise of 3:12 or less, meaning they have a vertical rise of 3 feet for every 12 feet of length. EPDM is less expensive than other roofing membranes and simple to install. It is usually black but can also be white, useful for reflecting heat. The sheets are 7.5 to 50 feet wide and .045 to .060 inch thick. EPDM is glued to a roof with adhesives or fastened mechanically. When it is fastened mechanically, a ballast of 2- to 3-inch-wide round river rock or pavers hold the membrane in place. The river rock is applied at the rate of 1,000 to 1,200 pounds of river rock per 100 square feet. Pavers usually weigh about 20 pounds per square foot. If it is installed properly, an EPDM rubber roof should last from 12 to 25 years.

Modified Bitumen

• Europeans developed sheets of bitumen modified with polymer plastics in the early 1960s. MB has been applied to roofs in the U.S. since the mid-1970s. It is marketed in rolls that are usually applied in two layers that form a membrane that is glued to the roof or applied with heat. MB rolls are typically 36 to 39 inches wide, and each roll covers 100 to 112 square feet. They are either smooth or are covered with granules of copper, aluminum, gravel or slag set in asphalt. There are two distinct forms, SBS and APP, each with distinct qualities.

SBS Modified Bitumen

• When styrene butadiene styrene is added to bitumen, the bitumen acquires rubber-like qualities. The addition of 10 to 15 percent of SBS to modified bitumen allows it to be stretched up to six times its original length before it returns to its original size. SBS modified bitumen is applied to fiberglass mats or scrims that weigh from 1 to 2 ½ lbs per 100 square feet. SBS membranes are applied with hot asphalt using torches or with adhesives.

APP Modified Bitumen

• The addition of atactic propylene to bitumen gives it plastic-like properties. Bitumen containing 30 percent APP can be stretched up to half of its original length before it breaks. It does not return to its original size after it is stretched. MB modified with APP is applied to polyester mats that are able to stretch along with the bitumen. APP modified bitumen has asphalt on the back that must be heated by a torch for application.