Understanding biogenic carbon accounting in wood EPDs

Biogenic carbon accounting plays a critical role in understanding the climate impacts of wood-based construction materials. This knowledge item explores how biogenic carbon is treated in Environmental Product Declarations (EPDs) for wood products, why it matters, and what practitioners need to know to interpret EPDs accurately and responsibly.

What Is Biogenic Carbon?

Biogenic carbon refers to carbon stored in organic materials such as wood. Trees absorb carbon dioxide during growth and store it in their biomass. When timber is used in construction, this carbon remains locked in the material for decades, reducing overall emissions.

Key Issues in Biogenic Carbon Accounting

Environmental Product Declarations (EPDs) provide transparent data on a product’s environmental impact. Including biogenic carbon in wood EPDs ensures accurate reporting of carbon storage and emissions. This information helps architects and developers compare materials and choose low-carbon options. There are key issues in reporting biogenic carbon:

1. Inconsistent Reporting Across EPDs
   EPDs for wood products often differ in how they report biogenic carbon. Some include it in the product stage (A1-A3), while others report it separately or not at all. This inconsistency can lead to confusion or misinterpretation of a product’s climate impact.
2. Temporary vs. Permanent Storage
   The climate benefit of storing biogenic carbon depends on how long the carbon remains sequestered. If wood is burned or decomposes at end-of-life, the carbon is released back into the atmosphere. Therefore, assumptions about end-of-life scenarios are crucial.
3. System Boundaries and Assumptions
   The treatment of biogenic carbon is influenced by the system boundaries defined in the EPD. For example, cradle-to-gate EPDs may show a negative carbon footprint due to carbon storage, but this doesn’t account for emissions at end-of-life.

Why This Matters

Recognising biogenic carbon in EPDs highlights timber’s role in climate mitigation. It supports life cycle assessments and informs procurement strategies. As a result, timber becomes a preferred choice for projects aiming to reduce embodied carbon.

Accurate biogenic carbon accounting is essential for designers and specifiers who want to make informed material choices; policy makers developing carbon regulations and incentives and LCA practitioners conducting whole-building life cycle assessments. Misinterpretation can lead to overestimating the climate benefits of wood, undermining efforts to reduce embodied carbon in buildings.

Recommendations for Practitioners

• Read EPDs carefully: Look for how biogenic carbon is reported and what assumptions are made about end-of-life.
• Use whole-life carbon assessments: Evaluate materials across their full life cycle, not just the product stage.
• Advocate for transparency: Support harmonized reporting standards that clearly communicate biogenic carbon flows.

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