Local government holds the pen on many of our infrastructure planning and regulations and specifies the build materials. By Jeremy Sole, Executive Officer, Sustainable Steel Council.
The choices made at the early stages of building and infrastructure projects don’t just affect short-term budgets or construction timelines, they influence the environmental legacy of public assets for decades, sometimes generations, to come.
Too often, material choices are praised or rejected based on their initial environmental profile, with little consideration for how those materials perform or degrade throughout their full life cycle, or what happens to them at the end of their useful life.
In short, we’re optimising for the build, not the long-term outcome.
Local authorities, as stewards of public land, budget and infrastructure, have both the opportunity and the obligation to lead by example. This means adopting a whole-of-life approach in procurement and asset planning.
Timber is frequently viewed as the ‘greenest’ building material. Yet, most structural timber in our country is treated with chromated copper arsenate (CCA) to protect against decay. When disposed of in landfill, CCA-treated timber releases toxic heavy metals into soil and groundwater. It also emits greenhouse gases as it breaks down. Engineered timber products (such as LVL and glulam) often contain synthetic adhesives that complicate recycling and disposal. In practice, a large share of timber from deconstructed buildings ends up buried or burned, not reused.
Local authorities, who often manage landfills or oversee demolition, will likely know the end-of-life burden of treated timber is significant – and growing. This was certainly front of mind after the Canterbury earthquakes.
Steel and concrete have traditionally been seen as carbon-intensive. But that picture is changing fast, with innovations making them more circular and lower in carbon, both in production and over their life span.
Concrete formulations now include recycled aggregates and new cement blends that can reduce embodied carbon dioxide by up to 70 per cent, with 20–30 per cent reductions already achievable in most New Zealand contexts.
Steel, meanwhile, is on the cusp of a major transformation. The Glenbrook steel mill’s transition to an electric arc furnace (EAF), due to be operational in late 2025, will allow steel to be made from scrap using renewable electricity. Steel also has a major advantage: true circularity. It can be reused, remelted, or repurposed infinitely without losing quality, unlike timber or concrete.
A recent example is the Hinuera Sheds project in Waikato, where nearly 200 tonnes of demolition steel from a 1990s port was reused structurally. With thoughtful design and verification, reused steel can meet performance and safety standards while drastically lowering the carbon cost.
Over-specification is a common issue in public projects, particularly for structural steel. Many designs include far more material than necessary, in some cases, double or triple the optimal amount.
This has both environmental and financial implications. Councils and CCOs (council-controlled organisations) can benefit from early engagement with engineers and suppliers to ensure materials are optimised over their entire life span, and not just the comparatively short life of the structure itself.
Councils are uniquely placed to adopt a leadership role in sustainable construction, and to avoid unintended consequences down the line.
At the Sustainable Steel Council, we don’t advocate for one material over another. Steel, timber and concrete all have critical roles in a resilient built environment. What we advocate for is transparency, accountability and integrity in material decisions.
If we reward timber for carbon dioxide sequestration during growth, we must also address its toxicity at end of life. If we penalise steel for historic emissions, we should also recognise its recyclability and rapid decarbonisation. If we criticise concrete for its emissions, we should acknowledge its circular potential.
‘Sustainability’ means looking past appearances and assessing impact over decades, not just during construction.
Every material choice today shapes the legacy of tomorrow. Councils should ask: What happens to this material in 30, 50 or 100 years? Can it be reused or recycled? And will it become a liability – environmentally or financially?