We’re a third-generation custom building company here on Long Island. Back when the business was founded, tinsmiths generally installed all of a building’s flashing — window pans and heads, aprons, dormers, valleys, vents, gutters, chimneys. You name it, they flashed it, using sheet copper and traditional soldering methods.

Today most builders use lead to flash their chimneys, because it’s easy to work with and masons are used to installing it. But lead has its share of drawbacks: Folded corners create bulges that you have to work around, and the seams rely on caulking for a seal. Also, lead can tear at the worst possible moment — when you’re gently hammering it...

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