Salt air doesn't rot timber directly, but it accelerates the moisture cycling that does, and the species and finish decisions that work fine inland can underperform badly a hundred metres from the water.
What salt air actually does to timber
Salt itself doesn't feed decay fungi the way moisture does; the real damage mechanism is accelerated wetting and drying. Coastal air holds more moisture and deposits salt that is hygroscopic, it draws in additional moisture from the air, which keeps timber surfaces damp for longer stretches than the same species would experience inland.
That extended damp period is what decay fungi and dimensional movement both need. A timber that would comfortably dry out overnight inland may stay damp enough near the coast to support fungal activity, even in a species rated as naturally durable.
This is why coastal timber decisions can't simply copy an inland durability rating, the rating assumes a drying cycle that a coastal site doesn't reliably provide, especially in sheltered spots with poor airflow.
Comparing the common species
Teak's reputation for marine use is earned, its natural oils resist both moisture penetration and marine borers, and it moves less dimensionally than most alternatives as it wets and dries, which matters for anything with tight joinery. The cost reflects genuine performance, not just branding.
Iroko is a common, more affordable substitute with good natural durability, but it moves more with moisture than teak and can leach tannins that stain adjacent light-coloured surfaces, worth flagging to a client before it appears as an unexpected stain on a white render six months after installation.
Thermally modified timber (thermowood) is a different approach entirely: an ordinary species is heat-treated to change its cell structure, which improves dimensional stability and rot resistance without natural oils. It performs well in coastal conditions at a lower cost than teak, but the heat treatment does reduce the wood's structural strength, so it needs to be specified for cladding and decking, not load-bearing use.
Fixings and fasteners matter as much as the timber
A carefully chosen timber species undermined by the wrong fastener is a common and entirely avoidable failure. Standard steel fixings corrode quickly near the coast and can stain the timber around them; stainless steel, ideally grade 316, is the standard for coastal exterior fixing for the same reasons covered in our piece on exterior metal selection.
Tannin-rich species like teak and iroko can also corrode ordinary stainless fixings faster than the same fixing would corrode inland, and can react with certain metals to produce dark staining around the fastener, another reason fastener material should be chosen against the specific timber species, not as a generic default.
Fixing pattern matters too: timber expands and contracts across its width more than along its length as it wets and dries, so fixings need to allow that movement, over-tight or fully rigid fixing is a common cause of split boards in coastal decking within the first two seasons.
Finish, or leave it to weather naturally
Left unfinished, most durable coastal species weather to an even silver-grey over one to two seasons and then stay largely stable, a look many clients now actively choose. The tradeoff is that this natural patina is genuinely low-maintenance but not zero-maintenance: periodic gentle cleaning to remove salt buildup and algae still matters, especially in shaded, poorly ventilated spots.
An oiled finish keeps the timber's original colour but requires reapplication on a real schedule, typically annually in a coastal environment, more often on south- or west-facing surfaces that see the most sun and salt exposure, and a missed reapplication cycle can leave the timber looking patchier than if it had been left unfinished from the start.
The decision is best made explicitly with the client at design stage, in writing, because it is really a maintenance-commitment decision disguised as an aesthetic one, and the two options have genuinely different long-term cost and effort.
Where marine joinery experience carries over
Much of what governs exterior architectural timber near the coast is the same discipline used in yacht and boat joinery, species selection for moisture cycling, fastener compatibility, and finish maintenance schedules are all questions the group's marine services in Malta answer daily for teak decking and wooden boat restoration.
The scale and structural role differ, a building's cladding isn't subject to the constant flexing a boat deck experiences, but the underlying material science of timber, salt, and moisture cycling is the same, which is one of the genuine advantages of practising architecture inside a group with direct maritime materials experience.
Where a project sits directly on the waterfront and the exposure is closer to marine than architectural, borrowing from that marine joinery playbook, species choice, fastening detail, and a realistic maintenance schedule agreed with the client up front, tends to produce a more durable result than treating it as a standard inland detail relocated to the coast.