Building Expansion Joints


Designing for the movement of building components is an important part of architectural detailing. The movement can be the result of temperature changes, imposed loads, settlement, or other causes. Building expansion joints are used to cover the space between components, and provide a barrier to the exterior.

Expansion joints can follow complicated paths along varying materials. Copper is an excellent material for such joints, since it is easy to form and lasts a long time.

When detailing an expansion joint for a specific application, it is important to consider the magnitude and direction of movement. Some dimensions of details presented in this section are based on the expected maximum amount of expansion (labeled "E" in the details). Most expansion joints are optimized to accommodate movement in only one direction. Their ability to accommodate movement in other directions varies with their design. The designer should review the details and select the appropriate design based on particular requirements.

One issue that must be addressed in the proper design of expansion joints, is the height of curbs. This dimension depends largely on whether or not a cant strip is used at these locations. Normally, the minimum recommended curb height, measured above adjacent roofing, is 8 inches. However, if a cant strip is used, this dimension must be increased. If a typical 4" cant is used, the height of the curb should be a minimum of 10 inches above the adjacent roof. This leaves room for a minimum counterflashing lap of 4" and 1" to 2" space between the cant and the counterflashing.