Bitumen is a term applied to both coal tar pitch and asphalt products. Asphalt alternative roofing services were not standard in Houston or any other place in the world until the latter half of the 20th century. 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 (atactic 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 which led to modified bitumen roofing services becoming standard practice in Houston.

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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.