Single ply roofing systems are, as the name suggests, roofing systems consisting of one “ply” or “layer” or roof membrane. These systems are comprised of two families: Thermoplastics and Thermosets, each with many hybrids and evolutions.
Thermosets incorporate polymers that are cross linked or vulcanized. This means their properties cannot be changed and they can only be bonded with suitable adhesives. The most prevalent thermoset roofing membrane is EPDM (Ethylene Propylene Diene Monomer) which closely resembles a sheet of rubber. The seams of an EPDM roof are made using contact cement or double backed adhesive tape. Installation can be achieved by mechanically fastening, fully adhering or ballasting with stones such as river rock. These systems have been in the field for many decades and are well proven. Being a cured material they are basically inert and have a long service life.
Thermoplastics by definition can be repeatedly softened by heating and return to their normal state as they cool. This allows the seams on thermoplastic membranes to be heat welded or fused together using controlled hot air providing a permanent water tight seam. Similarly, all the detail components, such as pipe boots, are welded to the surface of the membrane.
The principle types of thermoplastic membranes are PVC (Polyvinyl Chloride) and TPO (Thermoplastic Olefin). These usually come in a light or white color finish which both reflects the solar spectrum and emits heat. Known as “cool roofs,” these characteristics bring them into compliance with California Building Code Title 24 part 6 designed to reduce heat entry into a building, thereby reducing the air conditioning load. All single-ply systems should be installed over a smooth surface. Usually this is accomplished by installing the membrane over insulation or a gypsum board faced on both sides with fiberglass. The membrane is secured to the substrate using mechanical fasteners or by fully adhering to the substrate.
Benefits of single-ply roofing:
- Positively water tight seams (thermoplastic)
- Generally white in color
- Compliant with California title 24.
Limitations of single-ply roofing:
- Initial cost can be higher than BUR systems. This initial cost can be offset by the lifetime of the roof.