The use of flat seam copper roofing in the United States dates back to the copper roofing manufactured by Paul Revere and installed on the Massachusetts State House in 1802. Since then, flat seam copper has been widely used in low-sloped roofing applications as it is a reliable, durable roofing material. History shows that flat seam copper roofing can provide a service life of 100 years, which the original Massachusetts State House roof achieved (Photo 1). However, flat seam copper roofing is expensive and is only as reliable as the quality of the seams between panels.
If the panels are improperly designed and installed, the service life of the roof can significantly be reduced (Photo 2). A common failure is cracking of the flat lock soldered copper seams and subsequent water leakage through the open seams (Photo 3). Although certain “best practice” guidelines by various sources have existed for years1, 2, 3, 4, the guidelines are based on practical experience instead of testing, and currently there is no industry consensus on what constitutes “acceptable” practice for constructing flat lock soldered copper seams based on in-service performance. In service, these joints are subjected to snow and wind loads, but the most demanding loads are the cyclical thermal stresses incurred during temperature swings.