According to NRCA's 2001-02 Low-Slope Roofing Materials Guide, there are more than 400 modified bitumen sheets available in the United States from at least 31 manufacturers/suppliers. The resulting number of potential membrane combinations is staggering—after selecting a supplier and membrane, a choice still must be made as to the most appropriate method of installation. There are more options than ever for adhering modified bitumen sheet materials, including hot asphalt, heat welding or torching, liquid cold adhesive, self-adhesive and mechanical fastening with a heat-welded overlap.
Following is some information about the benefits and drawbacks of these installation methods. Because self-adhered and mechanically fastened roof systems have relatively small market presences, they will not be addressed at length.
When SBS-modified bitumen products were introduced in the United States during the late 1970s, a majority of U.S. roofing contractors were installing built-up roof systems. Familiarity and practicality of using existing equipment made installing SBS-modified bitumen membranes using hot asphalt an easy choice. However, in the years since, laboratory testing and field experience have demonstrated that other interply bonding choices—solvent-based adhesives, heat welding and heat-activated self-adhesives—offer higher performance.