Copper roofing in Washington, DC

Copper is a detail metal on most Washington homes, not a whole-roof material. You find it on the projecting bays of Victorian and Romanesque rowhouses along Capitol Hill's east-west streets and in the older mansions around Dupont Circle, on the domed tops of round turrets, on dormer cheeks set into slate mansards, and on curved entry canopies above front doors.

In upper Northwest and the older close-in suburbs, copper often caps bay windows on Georgian and Federal revival homes, lines built-in gutters behind wood cornices, and forms the valleys of slate roofs. Many of these pieces date from the 1910s to the 1930s and are reaching the point where seams have fatigued from decades of expansion.

We also install copper on new work, such as a standing seam porch roof on a renovated colonial or a cupola on a carriage house. Copper's green patina takes years to develop, so new copper starts bright penny-colored, darkens to brown within months and slowly shifts toward green.

Flat-seam copper uses small rectangular pans, folded on all four edges, locked together and soldered. It is the traditional choice for low-slope bays, porch roofs and curved surfaces because the soldered seams stay watertight even when water moves slowly. Most original DC bay roofs are flat-seam.

Standing seam copper uses long panels with raised seams and concealed cleats, like steel standing seam but in a softer, heavier metal. It suits steeper slopes and larger roofs where the vertical lines suit the architecture.

Batten seam copper runs panels between raised wood battens capped with copper. It reads as a heavier, more formal look and appears on some turrets and institutional buildings. We pick the system based on pitch, shape and what was there originally, especially when historic review is involved.

• Flat-seam pans, soldered, for bays and low slopes
• Standing seam panels for steeper roofs and porches
• Batten seam for formal or historic profiles
• 16-ounce and 20-ounce sheet chosen by exposure

Copper soldering is slow work. Each seam is cleaned with a wire brush, fluxed, tinned and then flowed with tin-based solder containing no lead using a heated iron, not a torch. Good solder joints sweat all the way through the lock, leaving a smooth bead with no pinholes. A cold joint looks fine on the surface and leaks after the first freeze.

Expansion must be planned. A large bay roof made from one soldered sheet will crack as it moves with the seasons. We break larger surfaces into pans with expansion joints and loose-lock cleats so the copper can move.

Turrets are the hardest copper work we do. A conical roof gets tapered panels, each cut to a template and shaped over a form, then locked into the next panel and soldered at the finial. The finial itself is often spun or hand-raised copper, salvaged and refitted when possible.

In historic districts, copper is usually the expected replacement for original copper. The Historic Preservation Office wants to see the same seam type and profile, and on Georgetown houses the Old Georgetown Board has a say. We document the existing roof with photos and measured sketches before removing anything, and include that in the submission.

Copper and slate belong together. Slate roofs last a century, and copper flashings and valleys are the only metal that keeps pace. When we do slate repairs or full slate replacements, valleys, step flashing and ridge caps are copper.

Box gutters behind wood cornices on rowhouses were often lined with tin or copper originally. Relining them in copper costs more than modified bitumen, but lasts many times longer. Our box gutter work covers the cornice side of that job.

Copper's upfront cost is high because of the metal price and the hand labor. But a properly soldered copper roof can easily outlast the house's next two or three shingle roofs. On a bay roof, the per-year cost often ends up lower than cheaper metal that needs repainting and patching.

Copper doesn't need paint. The patina is its protection. The one thing to watch is contact with dissimilar metals: steel fasteners, aluminum gutters or galvanized flashing touching copper will corrode quickly, so every fastener and accessory we use with it is copper, brass or stainless.

Runoff from copper stains light stone, limestone sills and concrete green over time. We direct downspouts and drip edges so water lands where staining won't matter, or we warn you where it can't be avoided.

Insurance and resale both benefit from documentation. We hand over measured sketches, seam details and photos of the soldered joints, which help an appraiser or a buyer's inspector understand what they're looking at instead of guessing at the age of a patinated roof.