8 August 2025
Out in the South Pacific, 800 kilometres east of mainland Aotearoa New Zealand, the Chatham Islands endure a raw and unforgiving climate. With no surrounding landmass to soften the blow, the island is battered by salt-laden winds. For the 600 residents, building resilience isn’t optional – it’s essential.
Despite their remoteness, the Chatham Islands’ battle against the elements – especially extreme corrosion on their buildings – is nationally relevant. As climate change intensifies, these conditions could be a preview of what’s to come elsewhere in New Zealand by the end of the century.
Under New Zealand’s building standard for corrosion, the Chatham Islands had long been classified as ‘Zone D’, but there was no hard data to back it up. In 2021, the Building Research Association of New Zealand (BRANZ) joined forces with researchers from the Joint Centre for Disaster Research at Massey University, to investigate.
The first round of Chatham Island testing, across four sites, showed that corrosion levels were off the charts. An unprotected carbon steel plate (1mm thick) was completely gone within one year, despite lasting more than 50 years in NZ rural inland areas.
“If you use materials approved for Zone D corrosivity in the Chatham Islands, you will have early material failure,” BRANZ Senior Scientist Zhengwei Li says.
The community, already familiar with rusted-out woolsheds and other failing materials, requested more research after they heard the results of the first study. Seven new test sites were added. The results were even more extreme.
The tests showed that carbon steel, which is used in common building products like beams, framing and nuts and bolts, corrodes at a rate of 4447 g/m2/year on the Chatham Islands. This rate is:
- 22 times faster than inland rural New Zealand (less than 200g/m2/year),
- more than 3 times the rate of our harshest coastal sites, like Oteranga Bay on Wellington's south coast (1276g/m2/year)
- nearly double the highest rate recorded in Europe (2390g/m2/year).
Using the wrong materials here could mean early failure – and wasted investment. So, the researchers have connected with local schools, landowners, elders, builders, and Chatham Islands Council to develop solutions.
They are now working to create the first-ever corrosivity map for the islands, guiding future building and infrastructure decisions.
Leith Weitzel: Chatham Islands builder
“Building here isn’t just about putting up walls and roofs. You have to understand the land, the air, and the sea. The environment is tough; there’s salt in the air, peat in the soil, constant wind, and parts of buildings that don’t get rainwashed or maintained can deteriorate quickly.
“You need to choose the right materials. That’s not always easy – people often bring in kitset buildings or products that work fine on the mainland but aren’t suited to island conditions.
“One good example is when I built a pole shed out of roofing iron about 10 years ago. The parts that get regular rain still look new, but under the eaves where the rain doesn’t reach, the steel is already corroding and will soon rust through. Another time, I stored a bag of ungalvanised nails in a sealed box in my storage container. Eighteen months later, every nail was rusted.
“We need better awareness, among builders, homeowners, and suppliers, about what materials are truly durable in these conditions. The corrosion research is a great step. It’ll help build the evidence we need to make better choices here and across New Zealand.”
Dennis Prendeville (Ngāti Mutunga): Port worker, tour guide and sixth-generation Chatham Islander
“Rust is a constant issue here. Anything steel that isn’t galvanized will show rust in six months. Iron roofing only lasts about 25 years.
“We use number 8 wire for fencing along the coast - 4mm thick - because it resists rust better. Inland, thinner high-tensile wire can last over 25 years, but on the coast, it might only last 10. The wind causes the wire to rub against the staples, creating rust spots. In peat swamps, wire on the ground can rust through in just a year, so we often skip the bottom wires – we put in six rows of wire instead of eight.
“We have to invest in better materials - double-coated roofing iron, zinc-coated products -because cheaper options just don’t last. In the end, it’s the salt, wind, peat water, and road dust that do the most damage.”
[ENDS]
BRANZ's outdoor exposure sites across Aotearoa New Zealand
Testing building materials in the real world
At BRANZ, we don’t just test in the lab; we take it outside too. From Northland to Invercargill to the Chatham Islands, and even Hawai’i, we see how building materials really hold up in our toughest environments.
More than 25 testing sites give us real-world data on how materials age, corrode, and perform over time. We’ve been collecting this data since 1973, to understand how materials will withstand the elements for generations to come.
We test in places with:
- Salt-laden coastal winds to see how metals handle corrosion
- Geothermal emissions to help building materials to beat sulphur and heat
- Extreme UV and weather conditions that are unique to New Zealand
- Volcanic gas emissions and ash which is the focus of our Hawai’i site and Rotorua Geothermal Field collaboration with Massey University
Find out more about BRANZ's building materials testing.
ABOUT BRANZ
The Building Research Association of New Zealand (BRANZ) is a trusted, independent expert in building and construction.
We provide practical research, testing, quality assurance and expertise to help create more affordable, quality, resilient and sustainable buildings.
At our heart, we’re a team of scientists, engineers and professionals committed to making a real difference for Aotearoa New Zealand. branz.co.nz
We honour the legacy of the late Distinguished Professor David Johnston of Massey University, whose pioneering research on Rēkohu Chatham Islands laid the foundation for this work.