Roof expansion joints are used to minimize the effects of stresses and movements of a building’s components. The effects of these stresses have the potential to cause damage to the roof system by splitting, buckling or ridging. Expansion joints in a roof assembly must be located in the same location as the building’s structural expansion joints – although they may be required in other locations.
Where expansion joints are necessary, both the structural and roof expansion joint should occur in the same location, extend across the entire roof, and continue through to the roof edge or perimeter. Expansion joints should be designed to accommodate contraction, as well as expansion. For most low-slope membrane systems, expansion joints should be detailed and constructed to a height of 8 inches (200 mm) above the finished roof membrane. Typically, wood curbing secured to the substrate on both sides of the joint is flashed with the appropriate roof membrane. An expansion joint cover is then installed.