Salt is steel’s biggest enemy, and New Zealand has a lot of coastline. A shed that would last decades inland can corrode far sooner beside the surf if it’s built from the wrong materials. The fix isn’t to avoid steel near the sea. It’s to match the materials, fixings and maintenance to how close you are.
How far are you from the surf? #
Steel manufacturers group sites into environmental categories for their pre-painted products. A typical guide looks like this:
| Category | Typical location | Conditions |
| Moderate | About 500–1000 m from breaking surf, or near calm salt water such as estuaries. Most of New Zealand | Little or no salt deposit, occasional salt smell |
| Severe | About 100–500 m from breaking surf on exposed coasts | Light salt deposits, frequent salt smell |
| Very severe and extremely severe | Right on the shoreline, beside surf, jetties and wharves | Heavy salt deposits, constant salt smell |
Salt can travel further inland with strong prevailing winds, and anything within 100 m of salt water needs the manufacturer to confirm the warranty. Calm harbours are gentler than surf beaches, which is why estuary sites can sit in the moderate category.
Choosing the cladding #
Manufacturers make several grades of pre-painted steel with different resistance to salt. In its guidance, the top-end products carry warranties across all coastal categories, while some standard products are not recommended in the harshest zones. The right choice depends on your exact site, so we confirm it with the manufacturer for anything close to the sea.
Fixings, flashings and the frame #
- Fixings need to be rated for the environment. A great sheet held on with the wrong screws will still fail at the screws.
- Flashings, gutters and trims need to be compatible with the cladding, to avoid one metal corroding another.
- Frames, purlins and girts inside the building are sheltered from rain, but in a coastal building that also means salt isn’t washed off. Design and ventilation matter.
Maintenance near the sea #
Rain washes roofs, but walls and sheltered areas such as eaves, soffits and the undersides of gutters collect salt. Manufacturers’ maintenance guidance calls for more frequent manual washing as conditions get harsher, from about every 3 to 6 months in milder zones to monthly in the harshest. Gentle water and a soft brush are enough; avoid high-pressure water above 20 MPa.
Our experience #
Steelspan has delivered buildings in marine environments, including port and naval sites. Every coastal site is different, so there’s no one standard specification. We start with a thorough look at your location and how the building will be used, then work with manufacturers and engineers to specify the materials, fixings and details that will give you the best durability for that site.
Talk to Steelspan #
Tell us your address and how far you are from the water, and we’ll recommend materials for that exact site. Use our Easy Shed Quote or call 0800 787 726.
