Mechanical Seaming

Mechanical seaming is the joining of standing seam metal panels by folding their mating edges together with a tool. The result is a continuous, folded joint that is more weather resistant than a snap-together seam and allows the panels to be used on lower slopes.

Seam forms

• Single lock (90 degree). The upper edge is folded once over the adjoining edge.
• Double lock (180 degree). The fold is turned a second time so the edges are locked tightly together, the form traditionally used on copper and zinc roofing in Europe.
• Triple or 360-degree locks. Some proprietary systems roll the seam further for additional water resistance.

Double-lock seams are generally the most weather resistant and the most expensive of the common standing seam types.

Tools

• Hand seamers and tongs. Used to start seams, finish ends and work around details.
• Powered (electric) seamers. Machines that run along the seam, folding it in one or more passes. They are matched to the specific panel profile.
• Hand seaming tools for traditional work. On copper and zinc roofs in Europe, seams are often closed by hand with specialised tongs and mallets.

Use on low slopes

Canadian guidance notes that most architectural metal roofs are designed for slopes of 1:4 (3:12) or steeper, and that below that a machine- or mechanically-seamed standing seam is required, with seam sealant or tape adding to the seam's water resistance. Panel manufacturers publish their own minimum slopes for each seam type.

Practice notes

Seams are usually started by hand at the eave, then run with the seamer toward the ridge. Clips must be engaged in the seam before it is closed. Because the seamer is profile-specific, using the wrong tool can distort the seam and void the manufacturer's warranty. Mechanically seamed roofs are harder to dismantle and repair than snap-lock roofs, since seams must be opened with special tools.