TPO Roofing

TPO (thermoplastic polyolefin) is a single-ply roofing membrane based on polypropylene blended with ethylene-propylene rubber. It is a thermoplastic, so its seams are fused with hot air. TPO contains no chlorine and needs no liquid plasticisers, which distinguishes it from PVC.

History

TPO compounds were available in the 1980s, and the first TPO roofing sheets appeared in 1989. Early non-reinforced sheets had been replaced by fabric-reinforced versions by 1993. TPO sales grew quickly in the 2000s; one estimate says US TPO sales quadrupled those of other flat roofing materials between 2007 and 2012, and it was the most popular commercial low-slope covering in the US by about 2016.

Product standard

The US product standard is ASTM D6878, first published in 2003 using 45-mil sheets as its basis. Revisions in 2011 raised the minimum thickness of the layer over the scrim from 12 mils to 15 mils (0.30 to 0.38 mm) and lengthened heat ageing before testing from 28 to 224 days at 116 C (240 F). The 2013 edition required the weathering-side coating over the scrim to be at least 30% of nominal thickness. NRCA has advised designers to specify a minimum 60-mil sheet.

Sheets

Common thicknesses are 45 mil (1.1 mm) and 60 mil (1.5 mm), with 80 mil (2.0 mm) and thicker for greater puncture resistance. Sheets up to about 3.7 m (12 ft) wide reduce field seams. White is standard; grey, tan and black are also made. Fleece-backed versions are used for adhered and recover work.

Installation

TPO is most often mechanically fastened in the seams. It can also be fully adhered, induction welded or, less often, ballasted (ballast hides the reflective surface). Seams are welded with automatic or hand-held hot-air welders. Known workmanship risks include "cold" welds at start-stop points and T-joints, scorching, and difficulty re-welding sheets that have weathered.

Performance notes

Sources report that TPO is stiffer than some membranes, changes colour and texture with age, and has a shorter field history than EPDM, PVC or BUR. Laboratory ageing temperatures are far above typical rooftop temperatures; white membrane surfaces seldom exceed about 49-71 C (120-160 F).