Manual Elements

Expansion joints and single-plies

Roof expansion joints are used in roof systems to minimize the effects of stresses and movement of a building's components. Roof expansion joints prevent building stresses from splitting, buckling, ridging or damaging a roof system.

The expansion-joint detail for single-ply membranes has evolved through the years. The first expansion-joint detail appeared as Detail K-1 in the second edition of The NRCA Roofing and Waterproofing Manual published in 1985. This detail depicted an expansion joint specifically for PVC membrane roof systems. The expansion joint was constructed out of two wood nailers that essentially were sized to be the same height as the roof insulation. Compressible insulation was installed between the nailers. At the top surface, the joint was filled with flexible tubing and capped with a PVC flashing strip welded to the membrane on each side. The flexible tubing and flashing strip accommodated the expected movement.

The detail remained the same in the manual's third edition issued in 1989.

In 1995, the manual's fourth edition divided single-ply membrane roof systems into two categories—thermoplastics and thermosets—and the expansion-joint detail was shown in details TP-7 and TS-7.