Q. Can regular sheets of metal panel roofing be installed on a curved roof with a radius of 28 feet?

A. Daniel C. Jandzio, wood frame product manager at Fabral, a metal roofing manufacturer, responds: Regular metal roofing panels can often be installed in a curved application, depending upon the panel profile chosen and the radius of the curved roof. [Editor's Note 7/23: For an example of a standing seam metal roof fabricated to fit a flared eave, see "A Concave Metal Roof" by Wade Paquin, April/21] The minimum radius is 24 feet for through-fastened steel panels and 18 feet for through-fastened aluminum panels.

Standing-seam panels usually require a much larger radius — between 100 and 200 feet — for successful installation without pre-curving.

In general, panels with a shallower rib height and continuous corrugation pattern are easier to curve than panels with distinct high ribs and flat areas. Panel ribs will tend to flatten out as they are bent over a curve, and care must be used to maintain equal width at both ends of the sheets.

Many curved roofs are actually arches, not uniform circular segments, and the calculated radius may not be accurate. If in doubt, try bending a scrap panel over the tightest radius section of the arch to see if it will work.

Finally, curved applications typically require additional fasteners to resist the forces induced by curving the panels. Increase the number of fasteners in the field panels to the fastening pattern recommended by the manufacturer for eaves and endlaps. It may also be necessary to install stitch screws (short screws that join metal to metal without penetrating the substrate) in the sidelap where separation is apparent.