How to Calculate Embodied Carbon (2nd edition)

About this book

Published by the Institution of Structural Engineers in 2022, 'How to Calculate Embodied Carbon' in its second edition represents the primary methodological reference for practising structural engineers seeking to quantify, report, and ultimately reduce the greenhouse gas emissions locked into the materials and construction processes of buildings and infrastructure. The guide responds to the growing consensus that reaching net-zero carbon by 2050 requires not only improvements in operational energy efficiency but also a decisive reckoning with embodied carbon — the emissions generated before a building is occupied and throughout its eventual replacement and demolition. The guide's foundational commitment is to provide a consistent, transparent methodology across the engineering profession.

One of the persistent obstacles to meaningful embodied carbon reduction has been methodological fragmentation: different projects have been calculated using different system boundaries, different data sources, and different conventions for treating carbon that is stored in biological materials or released during demolition. The second edition addresses this directly by aligning its approach with established international and UK standards, including BS EN 15978 (the standard for assessing the sustainability of construction works using environmental performance of buildings) and BS EN 15804 (the core product standard governing the structure of environmental product declarations). It also aligns with the RICS Professional Statement on Whole Life Carbon Assessment for the Built Environment, ensuring that outputs from structural engineers integrate coherently with the broader multidisciplinary carbon accounting that quantity surveyors and project managers perform.

Central to the guide is a clear articulation of the life-cycle stages that embodied carbon calculations must address. The framework uses the familiar module notation from the EN standards: Modules A1 to A3 cover product manufacture (raw material extraction, transport to factory, and manufacturing itself); Module A4 covers transport to site; Module A5 covers construction and installation processes. Together, A1 through A5 define 'upfront carbon' — the emissions committed before a building enters service.

This upfront carbon receives particular emphasis because it is irreversible at the point of construction; operational carbon can be reduced by retrofitting or changing energy sources in later years, but embodied carbon in materials already installed cannot be un-emitted. Beyond upfront carbon, the guide addresses the whole-life perspective through Modules B1 to B5 (use-stage embodied impacts, including maintenance, replacement, and refurbishment) and Modules C1 to C4 (end-of-life: deconstruction, transport, waste processing, and disposal). Module D, which captures the net benefits or loads arising from reuse, recovery, and recycling beyond the system boundary, is also discussed, though typically reported separately from the whole-life total.

This comprehensive framing allows structural engineers to see how decisions made early in the design process — structural system selection, material specification, connection detailing — reverberate across decades of building life. The guide gives specific guidance on data sourcing, directing engineers toward environmental product declarations (EPDs) as the preferred data type, since these are independently verified and product-specific. Where EPDs are not available, the guide points to secondary databases including the ICE (Inventory of Carbon and Energy) database and, notably, the EC3 (Embodied Carbon in Construction Calculator) platform, a cloud-based tool that aggregates EPD data and allows comparative material benchmarking.

The guide also provides default values and simplified approaches for use in early design stages, recognising that rigorous EPD-based calculations are only practical once material specifications are sufficiently developed. The principle of proportionality — calibrating calculation effort to design stage and decision importance — is woven throughout. A substantial portion of the second edition is devoted to early design stage assessment, reflecting the profession's recognition that the most impactful carbon reduction decisions are made in the earliest phases of a project.

Structural engineers, who determine the type and quantity of primary structure, have disproportionate influence over a building's total embodied carbon. Choices between concrete and steel frame systems, between in-situ and precast elements, between different foundation strategies, and between conventional and low-carbon material specifications can shift whole-project embodied carbon by thirty percent or more. The guide equips engineers to make these comparisons confidently and to communicate the carbon implications of structural options to clients and design teams.

The second edition also introduced or refined several conceptual tools. The Structural Carbon Rating Scheme (SCORS) provides a benchmark-based rating that places a project's calculated structural carbon intensity into context relative to typical and best-practice performance for comparable building types. The Structural Carbon Tool, a freely available Excel-based calculation workbook, accompanies the guide and enables engineers to apply the methodology without requiring specialist software.

These supporting resources lower the barrier to entry for smaller practices and earlier-career engineers. Biogenic carbon — the carbon stored in timber and other bio-based materials, and the carbon released when those materials decay or burn at end of life — receives careful treatment. The guide adopts a conservative default assumption for sequestered biogenic carbon in the absence of product-specific data, while cautioning that the long-term fate of bio-based materials must be considered to avoid overclaiming climate benefits from biological sequestration.

For the green building community, the importance of this guide extends well beyond structural engineering. It represents a maturing of embodied carbon practice in the UK construction sector — a move from voluntary, heterogeneous reporting toward consistent, auditable, profession-wide measurement. The alignment with RICS whole-life carbon guidance ensures that structural engineers' contributions to embodied carbon assessments are compatible with whole-building analyses, supporting the integrated carbon management that credible net-zero strategies demand.