My company has done a fair amount of remodeling work on older homes, and over the years we've grown accustomed to working with copper, using it for roof flashings on both remodels and new construction, budget permitting. In addition to copper's attractive appearance and known durability, we like the ability to solder the seams, which allows us to efficiently prefabricate aprons at dormers and chimneys—we just couldn't do that with aluminum or galvanized metal. Granted, copper is more expensive and soldering takes time. But we end up with a one-piece, maintenance-free assembly that's easy to install and, I believe, more watertight than anything we could achieve with other flashing metals.
Most of the corner flashings we come across, even if made from copper, are modified step flashings, cut in place to wrap the corner of the wall or chimney, while the leg running along the roof slope laps the apron. Both pieces may or may not be set in sealant, and usually the outside corner where the counterflashing and step flashing meet is unattractive if left exposed by the roof's shingle coursing. Instead, for a more-effective and better-looking result, we integrate the exposed apron with the corner flashing using soldered lock seams. Whether it's for a single unit or for multiple dormers or chimneys, we make the flashing all at once on the ground, saving considerable time on the roof.
Starting out. We cut and bend lengths of 16-ounce copper for the apron using a metal brake (we use a Tapco Pro). We make both the vertical legs and the legs that run along the roof slope 4 to 5 inches long (see illustration, page 28). We hem the bottom edge of the apron, then bend a slight, 5-degree "kick" about an inch up from the hemmed edge. This crease provides a measure of reinforcement along the length of the exposed apron, helping it keep its shape.
Next, we bend the apron to the roof slope. We under-bend the angle to provide tension, which helps the apron stay tight to the roof when installed.
Corner pieces. Using tin snips and hand brakes (we use Malco's), we fabricate the corner pieces. We cut standard 8-by-8-inch copper step-flashing pieces to accommodate two locking seams, cutting an angle for plumb (see illustration, below). Then, we notch out the corners of the apron piece 3 1/2 inches in from the ends, make a 45-degree cut to the inside corner, and fold over two 1/2-inch seams. We leave the folds on the apron and corner pieces slightly open to help join them together.
Locking seams. With the corner piece "snapped" into place, we hammer flat the seams, then temporarily lock them together by creating a small dimple with a light tap on a nail. This little indent keeps the seam from slipping during soldering. We solder the lock seams from the back (for soldering tips, see the slideshow "Soldering Seams") and install a small bead of solder to cover the pinhole at the corner on both the interior and exterior sides. Be careful not to use excessive heat when soldering the exterior.
The finished assembly provides a clean-looking transition from the apron to the sidewall step flashing and allows for some flexibility if the shingle coursing doesn't line up with the dormer. This detail can be used on a variety of siding and roofing types—in this case, stucco-clad dormers with asphalt shingles.
