Local chimney cap replacement for Fernandina Beach homes

How a galvanized cap runs out of zinc

A galvanized cap is steel protected by a zinc layer that corrodes in the steel's place. The zinc wears away fastest where water lingers: along the screen wires, at folded seams, and around fastener holes.

Once it is gone in a spot, the steel beneath rusts, and rust takes up more room than the steel it came from, so the wires swell and break. Streaks of orange on the crown or the brick below are the visible sign of that stage. By then recoating is not practical, since the zinc cannot be put back on the roof, and the cap is replaced in a longer-lived metal with the old fasteners removed as well.

Copper caps and the fasteners they need

Copper and zinc-coated steel make a small battery when rain connects them, and the zinc and the steel lose. That is the reason a copper cap is fastened with copper or stainless hardware and kept clear of galvanized flashing or an old galvanized screen. Roofing metal suppliers publish the same rule for copper used anywhere on a roof.

When a copper cap replaces a galvanized one, every old screw and clip comes out of the crown. Any nearby galvanized part that has to stay, such as a flashing piece a roofer owns, is kept out of contact with the copper, and its position is noted.

Cap metal where salt reaches the roof

Salt carried on the wind settles on a cap and draws moisture to it, and chloride salt attacks metal that would last for years further inland. Some cap makers offer a Type 316 stainless line, sold as marine grade, for sites near salt water, since the molybdenum alloyed into 316 resists chloride pitting better than the common grade. A stainless-steel guide from the International Molybdenum Association adds that sheltered, rain-shadowed crevices hold salt longer than surfaces rain rinses, and a cap screen is full of such crevices. We follow the maker's grade guidance for the exposure, name the grade, and suggest rinsing the cap when the chimney is serviced.