TPO and PVC Single Ply Roof Membranes

What it is

A single layer of flexible polymer sheet — TPO (thermoplastic polyolefin) or PVC — laid over a roof deck and insulation, with seams joined by hot air welding.

Specification at a glance

Property	Typical specification
Standard	EN 13956
Thickness	1.2mm — 2.0mm
Reinforcement	Polyester scrim for dimensional stability
Seams	Hot air welded, tested
Attachment	Mechanically fastened, fully adhered, or ballasted
Reflectance	High for white membranes; stated SRI

TPO against PVC

	TPO	PVC
Chemical resistance	Good	Better, especially to grease
Plasticiser migration	None	Can stiffen over decades
Weldability	Good	Excellent, wider window
Cost	Lower	Higher
Typical use	General commercial roofs	Kitchens, chemical exposure

Where roofs actually fail

Not in the middle of the sheet. They fail at penetrations, upstands and terminations — pipe and duct penetrations, parapet upstands, outlets and junctions with vertical surfaces.

Which means the specification must cover the detail components: prefabricated corners, pipe boots, termination bars, sealant at the top edge, and a drainage design that keeps water moving to the outlets instead of ponding.

Where projects go wrong

• Seams welded in poor conditions without probe testing afterwards.
• Penetrations detailed on site rather than with prefabricated components.
• Ponding water from an inadequate fall, which shortens membrane life and finds any weak seam.
• Fastener pattern uniform across the roof, ignoring higher uplift at perimeters and corners.
• Incompatible materials in contact. Some insulation facings and bitumen products attack these membranes; compatibility must be confirmed.

Standards referenced

Flexible waterproofing sheets under EN 13956. Roof reflectance provisions under ECBC 2017. Wind uplift under IS 875 (Part 3).