Building Expansion Joints:
Roof Conditions

Description: Expansion joints in roofs require wood curbs around each roof area. The curbs should extend at least 8", or 10" if a cant is used, above the adjacent roof. In general, the top surface of the curbs should be sloped away from the joint, to shed condensation and moisture onto the roof. Insulation is often used in the expansion space, but is left out of the details for clarity.

The minimum recommended gauge for copper used on roof expansion joints is 16 ounces.

The following plates outline some common building expansion joint details. The noted dimension "E" is the total expected movement within the joint.

Special Conditions: When comparing details for roof expansion joints, it is important to consider the risk of physical damage to the joint. For example, if a catwalk is adjacent to or crosses a joint, the joint is more likely to be exposed to damage from people kicking or stepping on the joint, or from equipment being dropped or dragged over it. Some joint designs are inherently better at resisting these impacts, while others can be modified to improve their performance.

A. Building Expansion Joint at Roof

This detail shows a typical symmetrical copper roof expansion joint. It uses a copper cap to span the expansion space. Copper counterflashing is attached to the top surface of each curb with nails spaced no more than 3" O.C. A continuous copper lock strip holds the bottom of the counterflashing. The copper cap is loose locked onto the counterflashing, as shown to accommodate expansion and contraction movement.

B. Building Expansion Joint at Roof - Alternate

This design relies on manufactured elastomeric bellows secured to copper flanges. The bottom of the flanges are secured to each curb with a continuous copper edge strip. The size of the bellows depends on the maximum expansion movement and must be selected from the manufacturer's literature.

C. Building Expansion Joint at Parapet

This detail illustrates an expansion joint designed to accomodate the unequal movement of two portions in a building. The basic principle is that copper cap is attached to one curb while the other side is designed to accomodate movement. The end of the expansion joint cap is bent up where it meets the wall. A continuous lock strip is attached to the wall on each side of the expansion space. A vertical copper cap is folded into each lock strip. The lock strip on one side is designed to accommodate the maximum movement, while the cap is locked onto the other side (see section).

A copper cap is also formed to match the contours of the coping cover, and locked over the cover drip edge.

D. Building Expansion Joint Intersection

This detail shows an expansion joint intersection. The cover for the intersection is made of a single piece of copper. It is joined to the other caps with a 2" loose lock filled with elastic sealant.

E. Building Expansion Joint at Roof

This detail illustrates an asymmetrical design which uses wood blocking to help support the copper cap flashing. The blocking on each side is fastened to the curbs.

The copper cap is locked onto a continuous edge strip on one side. It extends over the expansion space, then down and underneath the other blocking. It is loose locked into a continuous edge strip. The dimensions should be calculated as shown to accomodate the expected movement.

F. Building Expansion Joint at Roof

This design for an expansion joint relies on flexing of the copper material to accomodate movement. This approach is acceptable as long as the radii of all bends that flex are at least 1/4".

The copper cap is formed into an inverted "V". Its height should be twice its width, as shown. The lower edges of the flashing are hooked onto continuous edge strips. Adjacent caps are joined with 3" sealant filled lap joints.