A roof that lasts decades in Nairobi can look tired within a few years in Mombasa or Kilifi. The steel is the same. The air is different: it carries salt, and it's humid most of the year. Here's what that does to a roof and how to specify one that holds up.
Why salt air is hard on roofs
Salt from the sea settles on metal as a fine deposit. When humidity is high, that deposit dissolves into a film of salty moisture, which corrodes metal far faster than plain rain would. Rain washes an open roof surface clean, but the underside of sheets, the eaves, the overlaps and anywhere sheltered stay damp and salty longest. That is why corrosion often starts under the overhang and at the edges, not on top.
The coating matters more than the steel
Corrosion life depends mostly on the metallic coating protecting the steel, not on how thick the steel is. Standard galvanized sheet has a zinc coating that is used up quickly in salty air. Alu-Zinc, an aluminium and zinc alloy, resists corrosion far better and lasts up to five times longer than standard galvanized. On the coast, it is the sheet we would specify first. Our Alu-Zinc vs. galvanized guide explains why.
For a coloured roof, choose a profile with a colour coat over an alu-zinc base, like our Colour Box Profile. Colour Box Profile and the plain Alu-Zinc 11/3 are both good coastal choices.
A coastal specification checklist
- Sheet: Alu-Zinc base, plain or colour-coated, rather than standard galvanized.
- Gauge: coastal areas also tend to be windy, so a thicker sheet (a lower gauge number) helps with wind uplift and flutter. See our gauge guide.
- Fasteners: use corrosion-resistant fasteners with sealing washers. A roof is only as durable as its screws, and a rusting fastener leaves a rust streak and a leak.
- Cut edges: keep cuts to a minimum, and avoid burning the coating with a grinder. Cut edges are where corrosion starts.
- Water shedding: make sure water can run off and nothing holds it. Ponding water and leaf litter in valleys and gutters speed up corrosion.
Maintenance that costs almost nothing
Rinse the roof with fresh water every few months, paying particular attention to the eaves and the underside of overhangs, which rain doesn't reach. Clear the gutters, and touch up any scratches promptly. A small routine like this can add years to a coastal roof.
Proven in the field
For a coastal distribution warehouse in Mombasa, we recommended Alu-Zinc over standard galvanized for exactly this reason. We deliver across the coast, including Mombasa and Kilifi. Tell us where your building is and we'll help you specify a roof that lasts.