History of Single-Ply Membranes

A single-ply membrane is a one-piece, factory-made waterproof sheet laid in a single layer over a low-slope roof, as opposed to the multiple plies of built-up roofing. Single-ply systems became possible after the growth of the synthetic rubber and plastics industries in the mid-20th century, and they now cover most new commercial flat roofs in North America.

Two families

• Thermosets are cured elastomers. The best known is EPDM (ethylene propylene diene monomer) rubber, the synthetic rubber most commonly used in single-ply roofing. Seams are joined with adhesives or tapes because the cured sheet cannot be re-melted.
• Thermoplastics, including PVC, KEE and TPO, soften with heat, so seams can be hot-air welded.

Milestones

• 1964: chlorosulfonated polyethylene (CSPE), sold by DuPont as Hypalon, entered roofing use.
• Early 1990s: thermoplastic polyolefin (TPO) membranes were introduced.
• Late 1990s: environmental concerns about chemical curing processes led some jurisdictions to restrict CSPE.
• June 2009: DuPont discontinued Hypalon; by about 2011 CSPE roofing had nearly disappeared from the US market.
• 2007-2012: TPO sales by the six major US manufacturers grew to about four times those of other flat-roofing materials.
• 2016: TPO was the most popular commercial low-slope roof covering in the US.

Market today

Thermoplastics (PVC, KEE and TPO) together account for more than 55% of the US commercial roofing market, while thermosets account for no more than about 10%. Studies from the 1980s to the early 2000s put the average life of thermoset membranes at 15-20 years, although products have changed since. EPDM is now commonly offered with warranties of up to 30 years.

Early EPDM and PVC

• EPDM: according to Roofing Contractor, EPDM single-ply membranes were first introduced in 1962. Their use grew in the 1970s, when the oil embargo raised the price of asphalt-based roofing. Early seams were cleaned with white gas and joined with neoprene-based splicing adhesive; butyl-based splice adhesives followed in the mid-1980s, and primers and double-sided seam tapes later still.
• PVC: according to Sika, chemists at the Swiss company Sarna developed the first fabric-reinforced PVC roofing membrane in 1962, later sold as Sarnafil.

Relation to modified bitumen

Polymer-modified bitumen sheets, developed in Europe from the 1960s or 1970s (sources differ), competed with single-ply membranes as the main replacement for multi-ply built-up roofing. Both technologies remain in wide use worldwide.