What is a standing seam metal roof?

What it is

Two things define standing seam: the seam stands up, and the fasteners hide. Each panel's edges are formed into a rib; adjacent ribs either snap together over a clip (snap-lock) or are folded over one another with a seaming tool (mechanically seamed, single- or double-lock, the tighter and more watertight of the two). The clips are screwed to the deck under the seam and let the panel slide as it expands and contracts with temperature, which a 40-foot panel does by a visible amount between January and July. Panels are commonly 12 to 18 inches wide, of coated steel, aluminium, and in premium work copper or zinc; the Metal Roofing Alliance describes the materials and finishes for residential use.

The IRC, Section R905.10 sets the slope: at least 3:12 for lapped, non-soldered seams without sealant, ½:12 with lap sealant, and ¼:12 for standing-seam systems, installed to the manufacturer's instructions over solid sheathing or spaced supports. The other metal roof — exposed-fastener panels screwed through the face, the barn and shed product — is regulated by the same section but is a different system with a different life, because every screw and its washer is a potential leak.

What it costs and who does it

Standing seam is priced by the square at a multiple of a shingle roof, with the metal and gauge, the finish, the seam type, the panel length (site-formed panels avoid end laps), the number of hips, valleys and penetrations, and the trim as the variables; the trim and flashing package is often a large share. It is specialist work: metal roofing contractors and sheet-metal shops with a panel machine, not every shingle crew. The directory's guide to metal roofing compares the systems, and its metal roof cost guide explains how the estimate is built.