Biogenic carbon in timber buildings – how should it be considered?
Timber plays a key role in decarbonising the construction sector by replacing carbon-intensive materials and supporting circular economy principles. Its ability to store biogenic carbon is a major advantage, but accounting for this in Life Cycle Assessments (LCA) is complex and often debated.
Carbon absorbed during tree growth remains stored in harvested wood products (HWPs) until decomposition or incineration. However, this should be treated separately from ongoing forest sequestration. Including future tree growth as a carbon offset in a building’s LCA is considered inappropriate and misleading.
Sustainably managed forests, when replanted, can result in greater overall carbon storage than unmanaged ones. Nonetheless, current guidance, such as from IStructE, advises that stored carbon should be assumed to be released at end-of-life, reflecting its temporary nature.
Ramboll’s approach is to separate biogenic carbon from building carbon assessments while recognising it in whole-life evaluations. Encouraging reuse and design for disassembly supports long-term carbon storage.
Projects like Woodcircles and initiatives such as CO₂ Removal Certificates (CORCs) are beginning to validate durable carbon storage. The industry must embrace circular design, advocate for supportive policy, and treat timber as a ‘carbon lease’—one that can be renewed through reuse.
