The three common choices fail in different ways and at different speeds near salt air. Picking the wrong one, or mixing two that shouldn't touch, shows up within a year or two, not decades.
Not all stainless steel is the same near salt water
Grade 304 stainless, the common general-purpose grade, resists rust in ordinary conditions but can develop pitting and crevice corrosion in a chloride-rich coastal environment, especially in sheltered spots where salt deposits aren't washed off by rain, under handrail brackets, behind fixings, inside welded joints.
Grade 316 adds molybdenum specifically to resist chloride pitting, and it is the standard choice for coastal exterior work for that reason. The price difference between 304 and 316 is modest compared to the cost of replacing corroded hardware within a few years.
Even 316 needs periodic rinsing in a marine environment, resistant is not the same as immune. Fixtures in sheltered, low-rainfall pockets of a facade should be flagged for manual cleaning specifically because they won't get the natural rinse the rest of the building does.
Galvanised steel: reliable, but the coating has a clock
Hot-dip galvanising protects steel by sacrificing the zinc coating first, the zinc corrodes preferentially so the steel underneath doesn't, which is effective and economical for structural steel that will be clad or hidden. But the zinc layer has a finite life that shortens meaningfully in a marine atmosphere compared to an inland one.
Once the zinc coating is locally breached, a scratch, a cut edge, a weld repair on site, the steel underneath is exposed and corrodes at that point with no further sacrificial protection unless the coating is properly repaired with a zinc-rich compound, not just painted over.
For visible, permanently exposed coastal structure, a balustrade, an exposed frame, galvanising alone is usually not the final answer; it's more often paired with a duplex system (galvanising plus a compatible paint or powder coat) that meaningfully extends service life beyond either protection used alone.
Aluminium: excellent, until it meets the wrong neighbour
Aluminium forms its own thin, stable oxide layer that resists further corrosion well in a marine atmosphere on its own, which is why window frames, curtain wall mullions, and louvres are so often specified in it near the coast. Left to itself, it performs reliably for decades.
The failure mode that catches people out is not aluminium corroding on its own, it's galvanic corrosion, which happens when aluminium is placed in direct contact with a more noble metal, most commonly stainless steel fixings, in the presence of moisture. The aluminium corrodes rapidly at the contact point while the stainless steel is unaffected.
The fix is simple and cheap when specified up front: isolate dissimilar metals with a non-conductive gasket, washer, or coating at every fixing point, and specify fixings in a metal compatible with the base material rather than whatever is on hand. This single detail, done wrong, is the most common preventable coastal metal failure we see.
A practical selection framework
For fixings, brackets, and hardware in direct salt exposure: grade 316 stainless, isolated from any dissimilar metal it touches. For structural steel that will be clad or is otherwise protected from direct exposure: hot-dip galvanising, with a duplex coating if any part remains visible. For window frames, louvres, and lightweight cladding: aluminium, with isolation gaskets at every steel or stainless fixing point.
Distance from the water and shelter from prevailing wind both matter as much as the material choice itself, a facade in a sheltered courtyard fifty metres from a facade facing the open sea can reasonably use a lighter material specification, which is where a genuine site-specific exposure assessment earns its cost back many times over.
Whatever is chosen, specify a maintenance interval alongside the material, inspection and rinsing schedules are cheap and dramatically extend service life, but only if someone actually owns that task after handover, which is worth naming explicitly in the maintenance manual rather than assuming.
The mistake that costs the most to fix later
Galvanic corrosion between dissimilar metals is disproportionately expensive to fix after the fact, because the damage is usually at the fixing points holding a facade element in place, repair means partial disassembly of exactly the part that's hardest to access, not a surface treatment.
It is also the easiest mistake to prevent, because it requires no material substitution, just isolation at the point of contact, specified once on the drawings and checked once during fixing installation.
If there is one line item worth double-checking on any coastal metalwork drawing before construction, it is this one: every point where two different metals touch, and whether an isolation detail is actually specified there.