The Florida Building Code addresses salt-air corrosion in a few specific places — TAS standards, AAMA specifications, and the wind-borne debris region maps — but the corrosion question on a particular roof is finer-grained than the code can describe. The salt content in the air at a barrier-island address is materially different from the salt content half a mile inland.
Here is what we specify on coastal work and why.
Fasteners
Within 1,500 feet of saltwater: 316 stainless steel, not 304. The chromium-nickel content in 316 includes molybdenum, which is what resists chloride pitting. 304 will fail within five to eight years of immediate exposure. 316 will last the life of the roof.
1,500 feet to one mile: 304 stainless steel is acceptable for most attachments; 316 for any exposed fastener (e.g., ridge caps, fascia trim).
Beyond one mile: galvanized is code-compliant but not what we use. The cost differential between hot-dip galvanized and 304 stainless on a typical residential roof is in the low thousands and the longevity differential is decades.
Flashings
Copper in coastal applications is the gold standard for a reason — the patina protects the metal beneath, and there is no galvanic action with copper fasteners or copper-set ridge.
Galvanized steel flashings begin to bleed within ten years on the immediate coast. The visible orange stain on a stucco wall above a window is almost always the head flashing going.
Aluminum is the most common modern flashing material and is acceptable inland. On the immediate coast, aluminum flashings should be either anodized or finished with a marine-grade PVDF paint. Bare aluminum oxidizes to white in three years and looks chalky against any darker stucco.
Gutters
A copper gutter on a slate or clay roof is correct because the metals match the rest of the assembly. An aluminum gutter on a slate roof is permissible because the gutter is downstream of the slate (no galvanic action), but the gutter itself will need replacement before the field does.
Steel gutters — including factory-coated steel — should not be specified within two miles of the coast. The coating will fail at the seams and the gutter will rust through within ten years.
A note on what owners often miss
The fasteners holding the gutters to the fascia are the single most common failure mode we see on coastal homes. They are buried, they are out of sight, and they are usually 1.5" galvanized screws holding 30 pounds of wet gutter in a 60 mph gust. We specify 2.5" stainless lag screws into the rafter tail wherever the fascia design allows. The cost is roughly $1.20 per fastener. The cost of a gutter that goes through a pool screen is considerably higher.
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