Water-based Single-ply 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. This Common Product (CP) describes a site-applied, single-component, water-based roofing membrane adhesive. While roofing membrane adhesives are typically marketed for use with either PVC, EPDM, or TPO membranes, or for use with both TPO and EPDM roofing membranes, some content is expected to be similar regardless of the type of membrane for which the adhesive is intended. Consequently, this CP is intended to capture content that is expected to be present in adhesives used on any type of single-ply roofing membrane. Fully adhered membranes, installed with adhesives, 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 water-based adhesives, however, cannot be applied at temperatures below 40 to 50°F. 

For horizontal applications most water-based adhesives are applied using a roller or sprayed onto the roofing substrate only. For vertical applications the adhesive is also applied to the back-side of the roofing membrane. The membrane is then applied to the roofing substrate while the adhesive is still wet, and pressure is applied to bond the membrane to the substrate. Sometimes, rather than requiring the membrane to be applied immediately, these adhesives contain a pigment that changes color to indicate when the membrane should be applied to the substrate, but these types of products were not found to be common. 

One advantage of water-based adhesives over solvent-based adhesives is that they contain fewer volatile organic compounds (VOCs) that contribute to photochemical smog formation. For this type of 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. It is important to note that under either definition, many exempt VOCs still have health or environmental hazards associated with them. Although water-based roofing membrane adhesives contain water as a diluent, toluene and methanol were both found to be common in products marketed for PVC roofing membranes. Consequently, while all products reviewed had less than 250 g/L VOC content, PVC roofing membranes usually contain higher levels of VOCs than adhesives marketed for TPO and EPDM membranes.