PVC Roofing

PVC (polyvinyl chloride) roofing is a thermoplastic single-ply membrane. Rigid PVC resin is made flexible with plasticisers and compounded with UV inhibitors, heat stabilisers, biocides and pigments, then formed into sheets, usually with polyester scrim or glass-fibre reinforcement. Seams are fused with hot air.

History

The first PVC roofs were installed in Europe in the early 1960s; vinyl membranes were developed in Germany and Switzerland and reached North America in the 1970s. ASTM D4434, the US standard for PVC sheet roofing, was published in 1985, making vinyl the first single-ply product with its own ASTM designation. The standard requires PVC resin to make up more than 50% of the polymer content.

Properties

• Weldability: heat-welded seams are homogeneous and strong; hot-air equipment softens both surfaces and a roller presses them together.
• Fire: vinyl is inherently self-extinguishing and performs well in fire testing.
• Chemicals: formulations resist ponded rainwater and common rooftop contaminants such as bird droppings and acid rain, and can be adjusted for greater chemical resistance.
• Reflectivity: white PVC typically reflects 80% or more of sunlight when new.

Typical thicknesses range from about 0.9 mm (0.036 in) to 3 mm (0.120 in).

Plasticiser loss

The main long-term concern is migration and evaporation of low-molecular-weight plasticisers, which can make older sheets shrink and stiffen. One approach is to blend in KEE, a high-molecular-weight polymer that does not migrate.

Recycling

Factory trimmings are recycled into new membrane and into products such as walkway pads.

Thickness and reinforcement

Thicker sheets give more puncture resistance and a greater wear layer. Reinforced sheets suit mechanically attached systems, while fleece-backed sheets are used for adhered and recover applications.