Using a Thermoplastic Membrane for Commercial Roofing Purposes
PVC is a major thermoplastic membrane in use on commercial buildings these days. PVC membranes can be laid using the fully adhered, mechanically attached, or the loose-laid ballasted method. The manufacturer's recommendations for laps, mechanical fasteners and cements should be followed when possible. The loose-laid method will require that a separator sheet be laid over the roof sheathing. The membrane is laid over this as described for thermoset membranes. Edge laps should be at least 2 inches and end laps 4 inches. The laps are sealed by chemical fusion or heat-welded. Heat welding uses hot air to melt the membrane, which is then rolled together.
Mechanically attached membranes can be fastened with PVC coated metal disks or bar-type fasteners as described for thermoset membranes. If PVC-coated metal discs are used, they are chemically welded or heat-welded to the roof membrane. The basic layout is the same as described for thermoset membranes. Fully adhered membranes are installed the same as thermoset membranes. Use the adhesive recommended by the manufacturer. Or contact us for more info. After the adhesive has been applied to the sheathing and bottom of the membrane on the commercial roof, let is set for the time required. Do not get the adhesive on the lap area, which will be sealed after the membrane has been laid and rolled smooth.
PVC flashing installation is about the same as described for thermoset flashing. Reinforced PVC flashing material is used. The roof membrane must be mechanically fastened to the sheathing in the area to be overlapped by the flashing. The flashing is chemically fused or heat-welded to the roof membrane. It is secured to the wall, chimney (we recently performed a related project in OKC involving a chimney flashing on a commercial building), or other butting surface with mechanical fasteners spaced 6 to 8 inches apart. The top edge is covered with counter-flashing.
Modified-bitumen membranes are sometimes installed on commercial buildings as single-ply roofing; however, more likely they will be applied as multiple-ply roofing in a manner similar to built-up roofing. They are applied with hot bitumen. The installation of these products can be tricky at times.