Although certain jobs with unusual shapes present challenges that may involve custom panels or flashings, manufacturers of residential metal roof systems typically offer a wide array of standardized accessories. These accessories are designed for eaves, gables, valleys, hips, ridges, pitch changes and roof-to-wall intersections. In some cases, a manufacturer may provide drawings for local fabrication of accessories as an alternative to buying preformed accessories.
Most residential eave details involve a drip edge that will direct water from a roof into a gutter or safely past the fascia. With standing-seam roof systems, the bottom edge of each panel is hemmed to wrap around the starter or drip edge. The standing-seam panels attach to the roof deck with clips and then are fastened at the top of the panels. For through-fastened vertical panels, as well as some shake and tile profile panels that cannot be locked into a starter, a manufacturer usually will provide closure strips and a clear procedure for holding the lowest course tight to the roof.
There are various methods for handling gables, usually dictated by the exact profile of the roofing panel being installed. There are three basic valley styles used with the various types of metal roofing -- a flat valley pan; one- or two-piece valley flashing; and a third valley option, often called an "open valley." There also is a variety of methods used for closing off ridges and hips. Most vertical panels will use lineal hip and ridge caps, usually in 10 lengths.
Situations such as slope changes and roof-to-wall intersections often will require custom-formed flashings to meet the exact roof shape. Manufacturers will provide suggested flashing designs, and you can bend these flashings on a portable brake or work with a local sheet-metal shop to have them custom fabricated. Skylights and chimneys also often will require special flashings though many of the major brand skylight manufacturers offer flashing kits designed to accommodate metal roofing. With regard to skylights and chimneys, it is important to remember there should not be a large dependence on sealants.
Although sealants can be used for aesthetic reasons and as backup water protection, the first line of defense with any metal roof flashing should be the flashing design. Extra security is achieved with sealant and underlayment.
Skylights should be on curbs that put them significantly above the highest point of the metal roof profile. On chimneys, the flashings should be cut into the masonry whenever possible. For roof-to-wall flashings, the flashings should be cut into or extend up behind the wall covering.
Attic vents and pipes should be handled per a roofing manufacturer's instructions. Several styles of pipe flashings are available that were designed specifically for metal roof systems. In some cases, these even will be available in matching colors.
Of course, as any experienced roofing contractor knows, just when you think you've encountered all unusual roof situations, something else comes along. In these cases, basic flashing design principles need to be remembered. It is important such flashings be designed to keep water flowing on top of the metal. However, the best-designed flashings often will feature redundant "backup" water channels beneath the roof panels for added safety and water protection. Another important thing to remember is to not create situations where roof debris, such as tree leaves, pine needles or ice and snow, may be trapped either by or in a flashing and cause water to back up the roof. Again, you should consult roofing manufacturers or The NRCA Architectural Sheet Metal and Metal Roofing Manual regarding the design of special flashings.