Embodied carbon: will low-carbon design decisions survive construction?

18 hours ago

5 min read

A project team selects a lower-carbon material during design. Months later, a contractor proposes an alternative because of cost, availability, constructability or scheduling. The material may still meet structural and technical requirements — but does it deliver the carbon outcome originally intended?

Who checks? What information is used? And how is the decision reflected in the project's final carbon assessment?

These questions are central to a new report from the World Business Council for Sustainable Development (WBCSD), Bridging Design and Construction for Carbon Alignment, published in September 2026.

BCSD Australia has examined the report alongside Australian embodied-carbon measurement, rating, specification and project-delivery initiatives to understand how businesses can use the findings alongside tools already available.

Where carbon information gets lost

Building designs increasingly incorporate embodied-carbon assessments, which help identify emissions associated with materials and construction processes.

But a design-stage assessment is based on information available at that time. As the project develops, material quantities are refined, products are selected, contractors price the work and procurement decisions respond to local conditions.

The WBCSD report shows how different teams can interpret the same design information differently — particularly where carbon assessments, building models, drawings, specifications and bills of quantities use different assumptions or classifications.

For example, an assessment may include an assumed quantity of reinforcement or a generic material emissions factor, while the construction team uses more detailed quantities or different product data. Both may be working from legitimate information, yet produce different results.

The challenge is to retain sufficient transparency to understand what changed, why it changed, who approved it and what it means for the carbon target.

What WBCSD recommends

WBCSD identifies eight practices for improving carbon-information handover between design and construction. They can be understood through four connected areas.

1. Establish the purpose and ownership of carbon decisions

Define the purpose of the assessment, engage cost estimators and contractors early, and establish owner-led governance.

2. Manage carbon as an ongoing project requirement

Use a Carbon Management Plan to set targets, reporting expectations, responsibilities and review points, rather than treating the initial assessment as a final answer.

3. Carry requirements into delivery documents

Place appropriate carbon-performance requirements in specifications and use building information modelling (BIM) to help connect elements with their underlying material and design assumptions.

4. Preserve traceability

Map design information to carbon and procurement classifications, and document assumptions, data sources, exclusions and confidence levels.

The report emphasises that BIM is valuable but should not be treated as the only authoritative source. Drawings, specifications, quantity information and other contractual documents remain essential.

What the evidence shows — and does not show

WBCSD's third-phase exercise used reference design information from a real project for a simulated handover between design and preconstruction teams.

It demonstrated differences in assessment approaches and highlighted information-management challenges. It did not test a live construction project's actual purchasing, material substitutions or final delivered carbon outcomes.

The report should therefore be understood as practical process guidance and an evidence-informed starting point, rather than proof of a particular carbon-reduction result.

How does this connect with work in Australia?

Measurement: national infrastructure guidance

The Embodied Carbon Measurement for Infrastructure: Technical Guidance, published by Infrastructure NSW and aligned with national adoption, supports consistent infrastructure emissions measurement and reporting.

The broader national decarbonisation resources include the National Embodied Carbon Databook and National Sustainable Procurement in Infrastructure Guideline.

Connection to WBCSD: Consistent measurement methods and data provide a foundation for comparing assessments as projects develop.

Building ratings: NABERS Embodied Carbon

NABERS Embodied Carbon provides a framework for assessing the upfront embodied carbon of eligible buildings following practical completion.

Its Embodied Carbon Rules, version 2.1, specify how relevant material and emissions information must be treated and supported by evidence.

Connection to WBCSD: Reliable evidence of materials, quantities and emissions supports the reconciliation of assessed carbon with actual project delivery.

Building performance: Green Star

The Green Building Council of Australia's Green Star Buildings rating system addresses upfront carbon within a broader set of building sustainability requirements.

The current Buildings v1.1 framework reflects continuing development of Australian project-performance expectations and alignment with NABERS.

Connection to WBCSD: Project sustainability and carbon-performance expectations need to be translated into documented design and delivery requirements.

Materials and substitution decisions: MECLA

The Materials and Embodied Carbon Leaders' Alliance (MECLA) has developed initiatives to strengthen demand for lower-carbon materials.

Its Show Me How to Deviate work addresses the practical challenge of proposing lower-carbon alternatives where existing material specifications or approval processes may create barriers.

Connection to WBCSD: Product alternatives and material substitutions require both technical approval and consideration of their carbon implications.

Project governance: Infrastructure NSW

Infrastructure NSW's Carbon Management Plan templates cover business case, planning/design/procurement, and construction/practical-completion stages.

They provide an example of how carbon-management responsibilities and reporting can be embedded across an infrastructure project life cycle.

Connection to WBCSD: Maintaining the carbon-management process across project stages is an existing practical expectation in relevant Australian infrastructure delivery settings.

Five questions for Australian project teams

The WBCSD report and Australian resources provide a useful basis for reviewing how embodied carbon is managed within an individual project.

Question	What to examine
1. Is the carbon target a delivery requirement?	Whether the owner has documented the target, its status, contractual implications and accountable decision-makers.
2. Are low-carbon requirements reflected in specifications?	Whether performance criteria, supporting evidence and approval arrangements are clear to suppliers and contractors.
3. Do cost and carbon calculations use reconcilable information?	Whether quantities, exclusions, material assumptions and data classifications can be compared across teams.
4. Are changes assessed before approval?	Whether substitutions and other design or procurement changes are evaluated for carbon as well as cost, technical suitability and schedule.
5. Can the final outcome be explained?	Whether records allow the project team to reconcile the original intent, key changes, actual material information and final assessment.

These are review questions, not a new rating methodology or substitute for existing technical requirements.

They can be incorporated into existing project governance, design reviews, procurement processes and carbon-management plans.

What this means for business

For asset owners and developers, the priority is ensuring carbon expectations have sufficient authority, ownership and evidence requirements to influence delivery decisions.

For designers and technical advisers, it is communicating not just the assessed carbon result but the assumptions and specifications on which that result depends.

For contractors and procurement teams, it is testing product availability, constructability and material alternatives while keeping the carbon consequences visible.

For sustainability and reporting teams, it is maintaining confidence that reported outcomes can be traced to the information and decisions underlying the project.

The business benefit is not simply more carbon data. It is better-informed decisions, clearer responsibility, less avoidable reconciliation work and a more credible explanation of carbon performance.

Connecting international practice with Australian delivery

WBCSD's report provides a useful framework for examining an important transition in project delivery: from calculating expected embodied carbon to managing the decisions that determine actual outcomes.

Australia already has substantial measurement, certification, materials and carbon-management resources. Their different purposes make it important for project teams to understand how they fit together.

For businesses, the next step is practical: review the handover points in an existing project, identify where carbon assumptions or responsibilities may change, and use the relevant Australian tools to ensure those decisions remain traceable.

That is how low-carbon design intent can be carried forward into the decisions that shape what ultimately gets built.