For over one hundred years until the last quarter of the 20th Century, specifying a roof system for any flat commercial building in the United States was a relatively simple task. Only one type of roofing system was used: a “built-up roof” composed of layers of fabric (or roofing “felts”) embedded in applied coatings of hot tar or asphalt. For the specifier, the only question was how many layers to install: two, three, or four? But the process of installing layers of hot, smoky asphalt is both labor-intensive and hazardous. And by the 1970s, new roofing types were developed that required less labor and posed fewer worker hazards. These new alternatives included an alphabet soup of chemical polymers – PVC, SBS, APP, EPDM, and more. They all offered installation savings and performance benefits, although at the expense of increased confusion in the marketplace. As a result, the specification and selection of a commercial roofing system became a more complex undertaking, requiring an increased understanding of the key functions of roofing systems as well as a detailed knowledge of the many different commercial roofing types.
