Modified Bitumen

Built–Up Roofing Membranes (BUR)

With Built-Up roofing systems, the highly reliable waterproof membrane is field fabricated with layers of bitumen, alternating with plies of reinforcing felts. The redundant layers give it exceptional resistance to water and weather. Johns Manville has been a leader in BUR with 150 years of experience. We manufacture a complete line of fiber glass felts, including ply and base felts, and mineral surfaced cap sheets.

Built-Up Roofing System — GlasKap® CR Cool Roof

When considering cool roof alternatives using a bituminous built-up roofing system, there is no easier solution than JM™'s GlasKap® CR Cool Roof Cap Sheet. GlasKap CR is an improved version of our proven GlasKap sheet, with added reflectivity and emissivity properties that meet CRRC (Cool Roof Rating Council), Title 24 (for California) and LEED® (Leadership in Energy and Environmental Design) requirements.

Bitumen History

A bitumen is a term applied to both coal tar pitch and asphalt products.

Modified Bitumens were developed in Europe in the 1970s when Europeans became concerned with the lower performance standards of roofing asphalt. Modifiers were added to replace the plasticizers that had been removed by advanced methods in the distillation process.

The two most common modifiers are APP (attactic polypropylene) from Italy and SBS (styrene-butadiene-styrene) from France.

The United States started developing modified bitumen compounds in the late 1970s and early 1980s. APP was added to asphalt to enhance aging characteristics and was applied to polyester, fiberglass, or polyester and fiberglass membranes to form a sheet good, cut in manageable lengths for handling.

Usually applied by heating up the underside of the roll with a torch provided a significant fire hazard and was outlawed in some municipalities when buildings caught fire and some burnt to the ground.

Another problem developed when a lack of standards allowed some manufacturers to produce goods with amounts of APP insufficient to enhance the aging characteristics.

SBS is used as a modifier for enhancing substandard asphalt and provides a degree of flexibility much like rubber. It also is applied to a myriad of carriers and produced as a sheet-good in rolls that can be easily handled.

SEBS - (styrene ethylene butadiene styrene) is a relatively new formulation increasing flexibility of the sheet and longevity.