Roof leaks in New England are almost always flashing failures. The roofing material itself — slate, cedar, metal — rarely fails first. The copper or galvanized steel at the chimney, the dormer, the skylight, the valley — that is where the water finds its way in. Correct flashing specification is not a secondary consideration. It is the specification that determines whether the roof performs.
Flashing is invisible in a correctly detailed roof. Step flashing runs up a wall beside a sloped roof, each piece overlapping the one below like shingles, tucked under the roofing material and bent up against the wall. Counter flashing covers the step flashing and is set into a reglet cut in the mortar joint above. Base flashing turns the corner at the low side of a chimney or wall. Valley flashing lines the angle where two roof slopes meet. None of it should be visible from the ground.
Copper is the correct flashing material for traditional New England roofing work. Sixteen-ounce copper for step and counter flashing; 20-ounce for base flashing, valley flashing, and any location with concentrated water flow. Galvanized steel is acceptable for concealed base flashing beneath finish materials but not for step and counter flashing that must last the life of the roof. Ice and water shield is a membrane, not a metal flashing — it is an underlayment, not a substitute for copper.
Copper step and counter flashing at a chimney or dormer, correctly installed with sealed reglets and properly lapped, lasts 50 to 75 years. The solder joints at corners and transitions are the first to fail — inspect them annually from the attic after heavy rain. Water stains on the attic rafters directly below a chimney or dormer indicate a flashing failure.
Copper flashing on a traditional New England roof — particularly with a slate or cedar shingle surface — is the correct specification because the flashing life should equal or exceed the roofing surface life. Aluminum flashing fails in 15 to 20 years. Galvanized steel fails in 20 to 30 years. Copper lasts 50 to 75 years. Spec the flashing to last as long as the roof.
Through roofing contractors who work in copper. This is not a general roofing contractor skill — copper flashing requires specific training. Ask for the contractor's copper flashing experience and ask to see examples of existing work.
Sixteen-ounce copper step and counter flashing at all roof-to-wall transitions; 20-ounce copper at all base flashing, valley flashing, and concentrated water flow locations, for traditional New England roofing. Counter flashing set in reglet cut in mortar joint, not surface-mounted. This is the specification that determines whether the roof leaks.
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