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:
| Type | Description | Common roofing use |
|---|---|---|
| 16 oz (per sq ft, equivalent to 0.0216 inch) | Most common roofing copper | Valley flashing, step flashing, chimney flashing, gutter |
| 20 oz | Heavier, used in commercial | Large flat surfaces, ornamental work |
| Lead-coated copper | Copper with lead coating; weather-aged grey appearance from day one | Historic restoration where verdigris (green patina) is undesired |
| Pre-patinated copper | Factory-aged to verdigris before install | When the design calls for green copper immediately |
For typical residential, 16 oz copper sheet (also written as 0.022 inch or 22 gauge equivalent) is the standard.
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.
NEVER attempt to solder copper flashing in a flammable environment (over felt underlayment, near wood deck, near combustible material). The soldering iron or torch heats copper above the ignition point of paper or wood. Use a flame-proof shield under the work area; clear combustibles within 3 ft of the work; have a Class B fire extinguisher within reach.
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
- Measure the chimney width plus 4 inches for end laps (for one wall of the chimney)
- Calculate how many step pieces are needed (one per shingle course up the chimney)
- Cut 16 oz copper into 12 x 12 inch squares
- From each square, mark the bend line at 6 inches
- Bend along the line to form the L-shape
Install
- Install the first piece flush with the eave; nail through the upper roof leg into the deck (single nail at the upper corner)
- Install the first shingle course over the lower roof leg of the first step
- Install the second step over the first, with 4 inch overlap of the chimney leg
- Install the second shingle course over the second step
- 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:
- Cut the strip 4 to 6 inches wide
- Length matches the chimney width
- Insert the upper edge into a chase cut into the mortar joint 1 to 1.5 inches deep
- Caulk the chase with polyurethane sealant
- 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
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.
- ASHRAE / NRCA guideline on copper flashing in coastal applications.
- Manuall internal: Roofing Roof Flashing Types, Roofing Repair Flashing, Roofing Slate Roof Maintenance.