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 that is absorbed from the atmosphere by plants through photosynthesis and stored in biomass—such as trees. When wood is harvested and used in construction, this carbon remains stored for the duration of the product’s life. However, how this carbon is accounted for in EPDs can vary significantly, affecting how we assess the climate benefits of wood.

Key Issues in Biogenic Carbon Accounting

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

Accurate biogenic carbon accounting is essential for:

• Designers and specifiers who want to make informed material choices.
• Policy makers developing carbon regulations and incentives.
• 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.

For a deeper dive, download the report on this page.