By Jeremy Sole, Executive Officer, Sustainable Steel Council
Embodied carbon is now firmly on the agenda for Aotearoa New Zealand’s construction sector. Designers, developers and clients are increasingly aware the emissions locked into buildings before they are even occupied matter just as much as the energy they consume over time. That shift is welcome – and long overdue.
But as attention on embodied carbon intensifies, there is a risk we repeat an old mistake: focusing on measurement without changing behaviour. One of the most persistent, yet least discussed, drivers of unnecessary embodied carbon in construction is overspecification – particularly in structural materials.
Put simply, many buildings contain more material than they need, and that excess carries real costs: higher embodied emissions, increased project costs and reduced accessibility to sustainable building for New Zealanders.
This is not a question of safety or competence. In certain contexts – hospitals, lifeline infrastructure and emergency facilities – conservative design margins are entirely appropriate. But across much of the commercial and industrial built environment, steel and other materials are routinely specified well beyond what performance requirements demand. Industry feedback suggests quantities 20 to 30 per cent higher than optimal are not uncommon in everyday commercial and residential projects. In some cases, the excess is much greater.
There's a cost
Every additional tonne specified carries a carbon cost. When a building contains 20 per cent more steel than required, it costs more to build, and it also carries 20 per cent more embodied emissions than necessary. At a time when New Zealand is working to meet binding climate targets, that excess is no longer benign. It undermines the very outcomes that sustainability frameworks are designed to achieve, as well as negating the hundreds of millions of dollars steel producers are investing in developing low-carbon manufacturing technologies.
Overspecification is often the product of legacy design rules, procurement or design shortcuts, risk transfer, or a desire for speed and certainty in a complex environment. Historically, it was rarely challenged. Material was relatively cheap, carbon was invisible, and the environmental consequences sat outside the project boundary. That context has changed.
Green Star has played an important role in accelerating industry focus on embodied carbon and lifecycle performance. Critically, it does more than measure – through its increasingly stringent reduction targets, it drives genuine emissions performance across the buildings it certifies. Its emphasis on transparency, documentation and continuous improvement has helped shift the conversation from intentions to outcomes.
The Green Star As-Built and NZ Green Star Buildings tools, with their performance-based approach focusing on supply chain transparency and mandatory carbon reduction, provide both the measurement framework and the accountability the industry needs. Now we need to couple that framework with optimisation in design and specification to fully realise its potential.
Reducing upfront carbon – the emissions embodied in materials at the point of construction – is the most direct lever available to us today. These are emissions we can measure, verify and act on now, without relying on assumptions about what may or may not happen to a building decades into the future. That is where the focus belongs.
Thinking long term
At the same time, taking a whole-of-product-life perspective adds important context. Sustainability assessments that treat buildings as static objects at a single point in time miss the reality that individual components have very different lifecycles – and that the choices made today shape the carbon outcomes of future builds.
Steel, for example, can be reused, remelted and repurposed repeatedly without loss of quality – and in New Zealand, around 90 per cent of construction steel is recycled. When properly documented and designed for disassembly, structural steel components can re-enter the supply chain with minimal additional processing and emissions. These are genuine long-term benefits. But they are a complement to reducing upfront carbon, not a substitute for it. The immediate priority is getting the quantity and carbon intensity of materials right in the first place.
This low-carbon potential is lost if materials are overspecified, poorly documented, or treated as waste rather than resources. It is also lost if procurement decisions are made without verified information about carbon intensity, sourcing and downstream outcomes.
Get it independently certified
The Sustainable Steel Council developed its Green Star-recognised Responsible Products Certification to provide independent verification of environmental performance, governance and circular economy practices across the steel supply chain. For designers and builders working within Green Star projects, it offers confidence that the materials specified are not only lower carbon today, but aligned with credible, long-term sustainability outcomes.
Audited low-carbon steel is already available in New Zealand, defined as steel produced with emissions below 0.75 tonnes of CO₂ equivalent per tonne. As domestic and international production continues to decarbonise – including through increased reuse, recycling, and electric arc furnace technology – those emissions will fall further. But even the lowest-carbon steel cannot compensate for inefficient design.
Reducing embodied carbon is not about substituting one material for another by default. New Zealand needs timber, steel and concrete to deliver safe, resilient and adaptable buildings. The real opportunity lies in using the right material, in the right quantity, for the right purpose, and doing so with evidence rather than assumptions.
That requires earlier collaboration between designers, engineers and fabricators. It requires greater willingness to interrogate conservative defaults. And it requires clients to recognise that the lowest upfront cost or fastest programme does not always deliver the best environmental or financial outcome over time.
It also requires better information flow. Materials passports – which record what materials are used, where they are located in a structure and how they can be recovered – can transform buildings into future material banks. These align directly with Green Star Buildings NZ’s emphasis on supply chain transparency and circular economy principles. When combined with verified product audits and tools such as the NZGBC’s Embodied Carbon Guide, they enable genuinely circular outcomes rather than theoretical ones.
It's worth it
The prize is significant. Cutting overspecification reduces emissions immediately, without compromising safety or performance. It also reduces costs, making sustainable buildings more accessible – critical when BERL research shows that a large-scale transition to low-carbon homes could contribute around $150 billion to New Zealand’s economy. Designing with whole-of-product-life in mind ensures that today’s sustainability gains are not tomorrow’s liabilities.
New Zealand’s construction sector has made real progress on embodied carbon. Green Star certification, Net Zero commitments and growing industry expertise demonstrate genuine momentum. We now need to carefully consider the quantity of material we specify, questioning whether it is truly required, and taking responsibility for what happens to the structural elements when they are eventually repurposed.
If we are serious about meeting our climate goals and delivering the healthy, efficient buildings all New Zealanders deserve, overspecification can no longer be treated as a harmless insurance policy. It is a design decision with measurable and material consequences – and one we now have both the tools and the obligation to address.
Together, by combining rigorous measurement frameworks with optimised design, we can deliver buildings that are truly sustainable, resilient and fit for the future.
Jeremy Sole is Executive Officer of the Sustainable Steel Council, where he leads the development of independent audit framework and tools that support low-carbon, circular and responsible construction in New Zealand.
These views are those of Jeremy Sole, and not necessarily those of the NZ Green Building Council.