Low-VOC Solvent-based TPO/EPDM Roofing Membrane Adhesive

Single-ply roofing membranes can be adhered to roofing substrates in several ways including mechanical fasteners, loose-laid with gravel (ballasted), or through a variety of adhesive products. These adhesives are typically marketed for use with either PVC, EPDM, or TPO roofing membranes, or for use with both TPO and EPDM roofing membranes. This Common Product (CP) describes a site-applied, single component, solvent-based roofing adhesive that can be used with either EPDM or TPO roofing membranes. Adhesives used with PVC roofing membranes appear to be similar in content though they may use a different polymer. Because adhesives for PVC roofing membranes are commonly marketed as a separate product, they are not included in this CP. The adhesive is generally applied using a roller or sprayed onto both the roofing substrate and the back-side of the roofing membrane and allowed to flash off until it becomes tacky. The membrane is then applied to the roofing substrate, and pressure is applied until a permanent bond is created. Fully adhered membranes are seen as having several advantages over other installation methods. Compared to the use of mechanical fasteners, they help distribute uplift pressure evenly across the membrane reducing flutter. They also allow for the use of larger sheets resulting in fewer splices. In addition, they are lighter and easier to repair than ballasted systems. Most adhesives, however, cannot be applied at temperatures below 40°F, though some products can be applied at temperatures as low as 25°F. 

Adhesives also introduce additional chemicals of concern into the work site and the environment. Many of the chemicals used in solvent-based adhesives are volatile organic compounds (VOCs) that contribute to photochemical smog formation. Low-VOC formulations that limit the amount of VOCs are available but the definition of low VOC can vary. Because VOC regulations are based on reducing smog formation, VOCs that do not substantially contribute toward smog formation are exempt and not counted when determining total VOC content of a product. Two commonly referenced VOC definitions are from the U.S. EPA and from the California South Coast Air Quality Management District (SCAQMD). The U.S. EPA lists exempt VOCs in 40 CFR 51.100. SCAQMD Rule 1168 limits VOC emissions from adhesives and sealants, currently 250 g/L for this type of adhesive and 200 g/L starting in 2023, and Rule 102 sets a definition for exempt VOCs that follows closely with the the U.S. EPA definition, with a couple notable exceptions (see notes on the solvents in the common contents for additional information on which solvents are considered exempt). For instance, t-butyl acetate [540-88-5] is considered exempt by the U.S. EPA but not by SCAQMD. Consequently, formulations that meet the requirements of Rule 1168 appear to use p-chlorobenzotrifluoride [98-56-6], considered exempt by both agencies, more frequently. Products containing less than 250 g/L of VOCs using either definition are included in the scope of this CP. It is important to note that under either definition, many exempt VOCs still have health or environmental hazards associated with them.