SPRI — The recognized technical and statistical authority on the Single Ply Roofing Industry

SPRI - The recognized technical and statistical authority on the Single Ply Roofing Industry

Modified Bitumen Use on the Rise

July 1996

SPRI, the trade association representing manufacturers of flexible membrane roofing systems has seen through its market research, that the use of modified bitumen roofing systems has grown dramatically in the United States over the last 15 years. Originating in Europe, the first APP-modified system was applied in Italy in the 1950s and the first commercial SBS-modified system was installed in France in the late-1960s. Their usage spread to the U.S. beginning in the mid-1970s. By 1987, modified bitumen roof systems had captured approximately 15% of the total U.S. commercial roofing market and their market share has increased to approximately 22% in 1995.

Like thermoset and thermoplastic sheets, modified bitumen membranes are prefabricated, independent waterproofing layers. For low slope roofing, however, modified bitumen systems typically incorporate the multi-layer redundancy of built-up systems through the installation of modified bitumen base sheets or conventional fiberglass felts over which the prefabricated sheet membrane is applied. Modified bitumen materials are strong and offer long lasting protection from weather and UV exposure are often used as base flashings in both BUR and modified roof systems.

The majority of modified bitumen roof systems are typically categorized into two basic polymer groups: SBS (styrene-butadiene-styrene), an elastic type of-modified; and APP (atactic polypropylene), a plastic type modified. Modified bitumen membranes are composed of three primary elements: asphalt flux, polymer modifiers, and reinforcements. Secondary elements are fillers, fire retardant additives, and surfacing.

The rubber- or plastic-based modifiers extend the performance capabilities of asphaltic materials. The results of properly modified compounds are increased resistance to aging and improved mechanical properties at both high and low temperatures. Reinforcements commonly used in the U.S. are polyester and fiberglass, which are available in a variety of types and weights. Some manufacturers offer products which have a reinforcement composite of a polyester/fiberglass laminate. Surfacing materials include factory-applied ceramic granules, factory applied metal foil skins, and field-applied coatings.

Application methods have expanded to meet the demands of roofing contractors, design professionals, and environmental concerns. SBS roof systems have been developed to be applied with hot asphalt, torch, cold process adhesive, or self-adhered. APP roof systems are commonly applied by torch and in some cases by cold process adhesives. These systems meet a wide range of testing agencies’ approvals under destructive testing, earning ratings for fire, wind and hail performance.

SPRI - The recognized technical and statistical authority on the Single Ply Roofing Industry

The market distinction of modified bitumen membranes is product versatility to suit a wide variety of specific project demands. Manufacturers of modified bitumen roofing systems are able to select and combine bitumen modifiers to formulate and produce membranes with product specifications to meet a variety of end uses. In addition to roofing applications, these materials are also manufactured for use as below grade waterproofing, as tile underlayments, and in environmentally friendly geomembrane installations (e.g. pond liners).

With their solid history of performance and versatility, the outlook for modified bitumen systems is for further growth and market acceptance in North America. Modified bitumen manufacturers are continually pursuing manufacturing product improvements as well as expanded product offerings and specifications. Such developments will result in products which are more user friendly and extended membrane system performance in a variety of conditions. Specially surfaced modified bitumen finished sheets, in the form of special foils, colored granules and coatings will continue to grow in popularity for architectural applications. Additional emphasis will be placed on increasing applicator productivity, and application materials and methods will be refined to be both environmentally acceptable and to meet the ergonomic concerns of the workforce.

Overall, modified bitumen systems have been demonstrated to be effective, and SPRI member manufacturers have shown to be responsive to the evolving demands of installers, specifiers and end users. When innovations in modified bitumen technology are introduced into the marketplace, you can bet they will come from a SPRI member manufacturer.

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