Single-Ply Roofing

Single-ply roofing is a family of low-slope waterproofing systems in which the membrane is a single layer of flexible, factory-made polymer sheet rather than several plies built up on site. Sheets are joined at overlapping seams by heat welding (thermoplastics) or by tapes and adhesives (thermosets), and are secured by ballast, mechanical fasteners or adhesives.

Main families

• Thermoplastics soften when heated, so seams can be hot-air welded: PVC, KEE (ketone ethylene ester) blends, TPO and FPO (flexible polyolefin), and PIB (polyisobutylene).
• Thermosets are cured (vulcanised) rubber that cannot be re-melted: EPDM is the dominant example; CSPE (Hypalon) was another until it was discontinued.

History and market

PVC sheets were first installed in Europe in the early 1960s and EPDM entered US commercial roofing in the same decade. Single-ply use grew rapidly in North America in the 1970s and 1980s as bitumen prices rose and labour became scarce. TPO followed from 1989 and became the most widely installed low-slope covering in the US by the 2010s. In the UK the products are often called "polymeric single ply" and are typical on warehouses, factories and distribution centres.

Attachment methods

• Ballasted: loose-laid sheet held down by stone or pavers.
• Mechanically attached: fasteners and plates in the seams or through the sheet, or induction-welded plates.
• Fully adhered: bonded across the whole underside with adhesive, or via a fleece backing.

Advantages and limitations

Single-ply membranes are light, fast to install over large areas and available in white for cool-roof performance. Their main vulnerabilities are workmanship at seams and details, puncture from traffic or hail, and, for some thermoplastics, long-term loss of plasticisers or surface coating.

Organisations

Industry bodies include SPRI in the US (founded 1981), which writes ANSI/SPRI standards on wind design, edge systems and ballast, and the Single Ply Roofing Association in the UK.