The recently released Declaration de Chaillot is a timely reminder emissions don’t just come from how we operate buildings, but also from how we manufacture the materials used to construct them. The declaration highlights the substantial pollution generated through production, often overlooked in the public debate, and calls for better accounting of environmental impacts across the full lifecycle of buildings.

In New Zealand, the current narrative tends to focus on emissions during the construction and use phases. What’s often missing is what happens when those buildings reach the end of their lives. How reusable are the materials? How toxic are they in landfill? What are the real long-term consequences?

Take timber. It’s widely regarded as a “carbon sink” because of its ability to absorb CO₂ during growth. However, this benefit diminishes over time. When timber products reach the end of their life – whether through demolition, decay or disposal in landfill – that stored carbon is released back into the atmosphere. Depending on how the wood is treated, it can also release other toxic substances.

For example, CCA (chromated copper arsenate) treated timber, still used in many structures, leaches copper, chromium and arsenic into the soil and groundwater over time. Associate professor Clemens Altaner, of the University of Canterbury, has been forthright about this, stating: “To suggest that CCA-treated wood is a safe and environmentally friendly material is an insult to any right-thinking people.” (NZ Herald, June 10, 2021.)

Laminated timbers introduce additional chemicals such as formaldehyde, phenol-resorcinol and polyurethane, which can also become problematic at end of life. While some treated wood can be downcycled, in practice, much of it is simply buried – delaying, not eliminating, its environmental impact.

Historically, both concrete and steel have been high emitters of CO₂. But that is changing. Advances in concrete technology now allow for up to 70% reductions in embodied carbon through improved cement blends and recycled aggregates. Crucially, concrete can be crushed and reused as aggregate, closing part of the loop.

Steel, likewise, is undergoing a quiet revolution. With New Zealand’s first electric arc furnace (EAF) technology coming online this year and global advances in recycled steel production, steel’s embodied carbon can be cut by up to 70%. Even more promising is its circularity: when buildings are designed with disassembly in mind, steel elements can be reused in future structures with minimal processing and zero loss of quality.

This is well-articulated in HERA’s Low Carbon Design Framework, which outlines how steel can be designed for deconstruction and reused multiple times across building generations. This circularity is not a theoretical benefit – it‘s being achieved in practice and could mean steel carries close to zero additional embodied carbon in subsequent uses.

Here‘s the uncomfortable truth: if we credit timber with environmental benefits at the start of its life, but ignore its toxic, carbon-releasing end of life, we‘re not telling the full story. In contrast, steel’s environmental footprint can be amortised over multiple building cycles, improving its long-term sustainability credentials significantly.

At the Sustainable Steel Council, our aim is not to claim moral superiority for one material over another, but to call for a more honest, whole-of-life approach. One that accounts not just for how materials perform during a building’s useful life, but what happens before and after that.

If we continue to make short-term choices based on feel-good carbon accounting that serves today’s emissions targets – but leaves our grandchildren with toxic landfills and rising methane emissions – we are failing them.

We often hear about the need to embed kaitiakitanga in our decisions. That must include an honest appraisal of the full lifecycle of building materials, even when the outcomes challenge popular assumptions. Kotahitanga – working together for a shared future – demands it.

It‘s time to rebalance the narrative. Let‘s aim not just for greener buildings today, but for a genuinely sustainable built environment our grandchildren will thank us for.