For many years the New Zealand Green Building Council (NZGBC) received requests to create a clear, consistent framework for measuring and reporting the life-cycle greenhouse gas emissions associated with buildings and construction.
Last year, following substantial work and consultation with the sector, NZGBC launched the Embodied Carbon Methodology v2.0 which is designed to do just that.
Its purpose is to support meaningful carbon reductions across the sector by providing a nationally consistent, transparent, and comparable approach that can inform design decisions, procurement choices, and policy development.
By establishing a single, shared methodology, NZGBC aims to align industry practice, reduce confusion, and enable like-for-like comparison across projects, materials, and design options. The methodology is endorsed by Engineering NZ, The New Zealand Institute of Architects, and the Ministry of Business, Innovation and Employment (MBIE). The document builds on MBIE’s Whole of Life Embodied Carbon Assessment: Technical Methodology.
At its core, the NZGBC methodology follows a whole-of-life approach to embodied carbon, consistent with ISO 14040 and ISO 14044, and with building-specific standards such as EN 15978. Emissions are reported across defined life-cycle stages, including material extraction, product manufacture, construction, use, and end-of-life. This structure ensures that carbon impacts are assessed systematically and avoids selectively reporting only those stages that present a favourable outcome.
A key feature of the NZGBC methodology is its explicit and transparent treatment of biogenic carbon. Biogenic carbon refers to carbon flows associated with biological materials, most notably timber, where carbon is absorbed from the atmosphere during growth and potentially released again at end-of-life. While these flows are real and important, they behave differently from fossil carbon emissions (emissions from burning fossil fuels) and require careful accounting to avoid misinterpretation.
Under the NZGBC approach, biogenic carbon is required to be reported separately and is excluded entirely from upfront carbon totals (covering modules A1–A5).
This treatment is consistent with international standards, including ISO 14067 and EN 16485, which require biogenic carbon to be disclosed distinctly from fossil greenhouse gas emissions. The Royal Institution of Chartered Surveyors (RICS) Whole Life Carbon Assessment guidance similarly emphasises that biogenic carbon should not be used to offset or reduce reported upfront emissions, nor to justify lower apparent fossil emissions.
The primary justification for this approach is that upfront embodied carbon reporting is intended to drive immediate reductions in fossil emissions. The climate science is clear that reductions in near-term emissions are critical: fossil carbon released today has an immediate and cumulative warming impact, contributing directly to the risk of exceeding global temperature thresholds. Allowing biogenic carbon removals to reduce reported upfront emissions risks diluting this signal and undermining the urgency of reducing fossil-based production and construction processes.
We acknowledge that in the New Zealand context, evidence suggests that much treated timber is disposed of in landfill and does not readily biodegrade or re-emit carbon dioxide or methane over typical assessment timeframes. This is an important consideration and highlights that biogenic carbon dynamics are highly context-specific. However, this does not remove the underlying uncertainty: future waste management practices may change over time through shifts in regulation, technology, or market conditions.
There is a real possibility that New Zealand could move toward alternative end-of-life pathways for timber, such as energy recovery, incineration, or other forms of thermal processing. Under these scenarios, stored biogenic carbon would be rapidly released back to the atmosphere.
Because these future decisions sit outside the control of today’s project teams, treating biogenic storage as a guaranteed and permanent offset to upfront fossil emissions would rely on assumptions that cannot be confidently defended over the long term. NZGBC does not endorse presenting permanent sequestration in landfill as a scenario since this can easily be misinterpreted as being guaranteed.
What this means in practice is that claims such as “climate positive”, “net positive carbon”, or statements that a building stores more carbon than it emits are increasingly difficult to support under modern carbon accounting approaches.
As calculation methods mature, and as organisations such as NZGBC and international standards bodies converge on more robust frameworks, these claims no longer provide a clear or reliable picture of real climate impact. The focus is shifting away from headline labels and towards transparent and conservative reporting of what is actually emitted, when, and where.
It is also important to note that bio-based products typically already perform well in upfront embodied carbon reporting because they generally involve lower fossil emissions during manufacture than many mineral- or fossil-derived alternatives. This means that timber and other bio-based materials often retain a genuine advantage within the NZGBC methodology, even without counting biogenic carbon storage, and can play an important role in reducing fossil emissions when used appropriately.
This distinction is also critical for the credibility of net zero claims. The NZGBC methodology aligns with international best practice in not allowing biogenic carbon storage to be used as an offset to achieve net zero outcomes. Net zero should be grounded in the elimination, or deep reduction of, fossil emissions, with any remaining emissions addressed through high-quality, additional, and permanent carbon removals, rather than temporary or uncertain storage within materials.
Ultimately, the construction sector will make the greatest progress through transparency and consistent collective action. Rather than searching for silver bullets, the NZGBC methodology encourages robust measurement as the foundation for improvement. The sector already has the knowledge and technology needed to reduce (fossil) embodied carbon at scale.
By unifying around consistent methods and focusing on real near-term emissions reductions, we can move forward together to deliver meaningful and lasting climate outcomes for New Zealand’s built environment.