Metal Roofing Options, continued

Standing-Seam Roofing

Standing-seam roofing takes its name from the vertical ridges created where the roll-formed panels are joined at the edges. In traditional standing-seam construction, L-shaped metal cleats nailed to the deck or spaced purlins are crimped between adjoining panels to provide a watertight joint that also locks the roofing in place. The absence of exposed fasteners gives it a more finished look than nail- or screw-down panels, making it a popular choice for a wide variety of traditional and contemporary building types.

Site-fabricated roofing. In the past, all standing-seam roofing was made from metal plates or sheets that were formed into panels with hand tools on the job site. Today, coil stock is used instead of plates or sheets, and mechanized metal-forming equipment has made the process faster and easier (Figure 5). Factory-produced panels are also available, and although they can be difficult to ship (unlike exposed-fastener panels, they can't be stacked, so manufacturers often charge a premium for the necessary crating and handling), some roofers feel that the heavier stationary equipment results in a better-quality product. Jerry Iselin notes that using factory-produced panels also increases the builder's chances of getting satisfaction if there are problems with the material. With a site-fabricated roof, you have only the roofer to deal with -- if he's uncooperative or out of business, you're out of luck.

Figure 5.Forming standing-seam panels on site used to mean folding and crimping sheet stock with hand tools, but modern tow-behind roll-forming equipment can quickly make standing-seam and exposed-fastener panels to virtually any length.

Self-locking panels. Traditional standing-seam roofing calls for special tools like brakes and shears, and installers need advanced metalworking skills more often associated with custom duct fabricating than roofing. To streamline the process, many roofers are turning to so-called snap lock panels, which can be assembled without crimping (Figure 6).

Figure 6.Motorized crimpers (top) seam panels with little effort but lots of time. Manufacturers are now producing snap-together panels that look hand-seamed but install faster (bottom).

Underlayment. While other types of metal roofing can be installed directly over existing roofing, Frank Farmer of American Roofs won't put a standing-seam roof over anything but a flat deck. According to Farmer, surface irregularities created by the old roofing will bind the panels, preventing them from moving with changes in temperature. The resulting ripples in the flat sections of the panel, or "oil-canning," are painfully obvious. "The one time we tried it, we ended up removing half the roof that was already installed because it looked terrible," Farmer says.

Some standing-seam installers will leave the old roofing in place, installing the new roofing over wood or metal purlins spaced 24 inches on-center, running parallel to the eaves. In addition to providing a smooth surface, the purlins provide convenient footholds for working on steep slopes, and they can be shimmed to compensate for sagging rafters or other surface irregularities.

Modular Panels

Pressed into lightweight copper, steel, or aluminum to resemble shakes, shingles, or tiles, modular panels are the newest and fastest-growing segment of the industry (Figure 7). Consumers appreciate their traditional look, and installers familiar with asphalt shingles or tile can usually make an easy transition to metal without investing heavily in equipment or training.