Induction Welding (Roofing)

Induction welding is a mechanical attachment method for single-ply roofing in which the fasteners go under the membrane rather than through it. Steel plates coated with a heat-activated bonding material are screwed through the insulation into the deck in a grid. The membrane is then rolled out over them, and a hand-held or walk-behind induction tool is placed over each plate.

How it works

Induction heating uses a coil carrying high-frequency alternating current to create a rapidly changing magnetic field. A metal object in that field heats up from eddy currents and, in magnetic metals, hysteresis. Because plastics do not respond to the field directly, the metal plate acts as the heat source: it warms its coating and the underside of the membrane until they fuse.

Advantages

• the membrane is not punctured by fasteners in the field of the roof
• fastener patterns can be spread across the sheet rather than concentrated in seams
• wind loads are spread across many bonded points
• it avoids the large quantities of adhesive needed for full adhesion

Use

Induction-welded systems are used mainly with thermoplastic membranes such as TPO and PVC. Plate density is set by wind-uplift design, with more plates at perimeters and corners. Systems are tested and listed as assemblies by bodies such as FM Approvals and UL in North America.

Limitations

Correct heating is essential; under- or overheating weakens the bond. The method also depends on accurate plate layout so the installer can locate each plate under the sheet.