ASTM D6878

ASTM D6878/D6878M, Standard Specification for Thermoplastic Polyolefin Based Sheet Roofing, sets minimum material requirements for TPO roofing membranes. TPO is a heat-weldable single-ply membrane widely used on low-slope commercial roofs in North America and increasingly elsewhere. ASTM lists D6878/D6878M-26 as the active version.

What it covers

The specification applies to flexible sheet made with thermoplastic polyolefin as the principal polymer, intended for use as single-ply roofing exposed to the weather. Requirements include properties such as:

• overall sheet thickness and thickness of the coating over the reinforcing scrim
• breaking strength and elongation
• tearing strength
• low-temperature brittleness
• dimensional stability
• heat ageing and resistance to ultraviolet light and weathering

Like other ASTM membrane specifications, D6878 deals with the sheet as manufactured. In-place roof performance, such as fire rating, wind uplift and seam strength in the field, is covered by system tests and code requirements, for example UL 1897, FM 4470 and ASTM E108.

About TPO

TPO compounds blend a thermoplastic such as polypropylene or polyethylene with an elastomer such as EPDM, plus fillers and stabilizers. TPO resists ultraviolet degradation and is usually white or light-coloured, which makes it common where reflective "cool roof" performance is wanted. Seams are joined by hot-air welding.

The specification has been revised several times as the industry gained field experience with the material.

Market context

Thermoplastic membranes (TPO and PVC, plus KEE) together account for a large share of the US commercial roofing market. Competing single-ply membranes are PVC under ASTM D4434 and EPDM under ASTM D4637.

Outside North America

In Europe, flexible thermoplastic membranes are specified under a harmonised European standard for plastic and rubber roof waterproofing sheets, which covers several polymer types rather than TPO alone; polyolefin membranes there are often called FPO (flexible polyolefin).