Membrane roofs utilize a membrane formed from polymers such as ethylene propylene diene monomer rubber (EPDM), thermoplastic olefin (TPO), or polyvinyl chloride (PVC) as a waterproof barrier.  The membrane must be secured on the roof in some way.  There are a variety of different methods to do this including ballast (i.e., gravel), mechanical fasteners, and adhesives. 
The performance and regulatory demands on adhesive and other materials continues to evolve.  Typical adhesives used in roofing applications include polychloroprene- or neoprene-based adhesives.  However, these conventional roofing adhesives have aromatic solvents such as toluene or xylenes.  These solvents are under increasing environmental pressures as VOC regulations tighten.