Copper Flashing Fabrication

Why this matters

Copper flashing on a chimney, valley, or wall transition is the difference between a roof that needs flashing replacement every 25 years and one that lasts 80 to 100 years. Copper costs 5 to 10 times the price of galvanized for the same square footage but the service life ratio is even better. Customer-paid premium roofing projects (slate, tile, high-end shingle) demand copper flashing; quoting galvanized on a substantial slate roof is a bid-killer because the flashing fails first and brings the whole system down. The skill is sheet-metal fabrication on the roof: cutting, bending, soldering, and integrating with the roofing material. The supply of competent copper flashing fabricators is small in 2026 because the trade requires both roofing knowledge and sheet-metal training. Contractors who can do both command premium rates.

When to specify copper

Use copper flashing when:

• Roof life is 50+ years (slate, clay tile, concrete tile, premium synthetic)
• High-end residential where aesthetics matter
• Historic restoration on buildings where copper was original
• Coastal locations where galvanized fails to corrosion in 5 to 15 years
• Customer requests it specifically (architect or designer spec)

Use galvanized when:

• Asphalt-shingle reroof on a budget
• Roof life is 25 years or less (matches galvanized service life)
• Customer is price-sensitive and the visual aesthetic of copper is not valued

Copper grades

Copper sheet for roofing comes in several specifications:

For typical residential, 16 oz copper sheet is the standard. Order it by weight per square foot, not by gauge: ASTM B370 lists 16 oz cold-rolled copper at 0.0216 inch nominal thickness, and gauge numbers mean different thicknesses depending on which gauge table the supplier is reading from.

The patina process

New copper is bright copper-color (orange-pink). Over time:

• 6 to 12 months: dulls to brown
• 1 to 3 years: develops brown patina
• 5 to 15 years: develops green patina (verdigris)
• 15+ years: stable green patina indefinitely

Many customers love the bright copper at install and are unprepared for the brown phase. Set expectations: copper goes through stages; the final green color is the patina that protects the metal for the next 80 years.

The brown phase is sometimes accelerated with copper sealants but these typically do not last and the natural aging is more attractive long-term.

Tools and materials

• Copper sheet (16 oz, sized for the job; typically 36 inch x 96 inch or 48 inch x 96 inch panels)
• Sheet metal shears (hand shears for small work, electric shears for larger)
• Snips (left-cut, right-cut, straight-cut for different applications)
• Hammers: sheet metal hammer, ball-peen for forming
• Bending brake (siding-style or sheet-metal brake; for straight bends)
• Hand seamer (for hemming and lock-seam folds)
• Soldering iron (small torch or weighted iron, 1.5 lb minimum for copper work)
• Solder (50/50 tin-lead solder; soft solder for roofing)
• Flux (rosin or acid-based for copper)
• Brushes for flux application
• Clean rags
• Chalk line, square, measuring tape
• Drill and rivets (for some joints; soldered is preferred when possible)

Safety

Sheet metal edges are sharp; cut hands and arms are common injuries. Soldering produces heat and fumes; well-ventilated workspace is required.

Basic fabrication: chimney step flashing

Step flashing protects the joint between a roof and a chimney or wall. The flashing is a series of small L-shaped pieces, one per shingle course, with each piece overlapping the next in the water-flow direction.

Layout

A typical step flashing piece for an 8-inch reveal shingle course:

• 6 inches up the chimney
• 6 inches out onto the roof
• Total: 12 x 12 inch piece bent into an L

Cut the pieces

1. Measure the chimney width plus 4 inches for end laps (for one wall of the chimney)
2. Calculate how many step pieces are needed (one per shingle course up the chimney)
3. Cut 16 oz copper into 12 x 12 inch squares
4. From each square, mark the bend line at 6 inches
5. Bend along the line to form the L-shape

Install

1. Install the first piece flush with the eave; nail through the upper roof leg into the deck (single nail at the upper corner)
2. Install the first shingle course over the lower roof leg of the first step
3. Install the second step over the first, with 4 inch overlap of the chimney leg
4. Install the second shingle course over the second step
5. Continue up the chimney

The shingles cover the roof legs of the steps; the chimney legs are covered by counter-flashing (which is the next step).

Install counter-flashing

Counter-flashing is the upper flashing that sits over the chimney legs of the step flashing. It is cut into the chimney mortar joints (or attached to the chimney with reglet) and folded down over the step flashing legs.

Cut the counter-flashing from a continuous strip of copper:

1. Cut the strip 4 to 6 inches wide
2. Length matches the chimney width
3. Insert the upper edge into a chase cut into the mortar joint 1 to 1.5 inches deep
4. Caulk the chase with polyurethane sealant
5. The lower edge folds down over the step flashing chimney legs

The counter-flashing must overlap the step flashing by at least 4 inches to prevent water entry.

Valley flashing fabrication

Open valley flashing (visible copper down the valley between two roof planes) requires a different fabrication.

Layout

A typical open valley:

• 24 inch wide copper sheet
• Length matches valley length plus 12 inch overlap at each transition
• Hemmed edges (folded back 1 inch for strength)
• Center crimp (a 1/2 inch high ridge running down the valley center to direct water)

Cut and form

Start with a blank wider than the finished pan. The 24 inch finished width plus two 1 inch hems means a 26 inch blank. Miss this and you brake a valley that no longer covers the layout.

1. Cut the blank to length with hand snips or a shear. Never use an abrasive chop saw or a grinder on copper. The heat discolors the sheet and the steel particles it throws embed in the surface and rust-stain the pan within a season.
2. Deburr the cut edges. A raw edge cuts hands, cuts underlayment, and holds a curl that fights you on the brake.
3. Brake the hems. Bend each long edge back roughly 180 degrees, then flatten it with a mallet or in the brake. The hem stiffens the pan against oil canning, kills the sharp edge, and gives the water a defined edge to break from instead of wrapping underneath.
4. Form the center crimp. Set the rib on the exact valley centerline, and check it against your layout mark on both ends before you run it. The rib stops cross-flow, which is what sends water from a heavy plane up under the shingles on the light plane during a hard rain.
5. Check the pan flat on the deck before you fasten anything. A pan that rocks was braked out of square and will telegraph down the whole valley.

Handle copper with clean gloves. Skin oils, mud, and mortar splash all mark the sheet and show up as blotchy patina years later when the customer is looking straight at it.

Fasten with copper cleats along the outer edges only. No fastener goes through the pan in the water path, ever. Cleats let the pan move with temperature, which a nailed-down valley cannot do, and a restrained copper pan tears at its fasteners.

Lap the upper pan over the lower by the 12 inches called out in the layout, always shingle-fashion in the direction of flow. Keep laps loose-lapped rather than rigidly soldered on long runs so thermal movement has somewhere to go.

References

• ASTM B370 (Standard Specification for Copper Sheet and Strip for Building Construction).
• SMACNA Architectural Sheet Metal Manual, current edition.
• Copper Development Association (CDA) Copper in Architecture Handbook.
• NRCA Roofing Manual: Architectural Sheet Metal and Flashings, current edition.
• NFPA 51B (Fire Prevention During Welding, Cutting and Other Hot Work).
• Manuall internal: Roofing Roof Flashing Types, Roofing Repair Flashing, Roofing Slate Roof Maintenance.