Reference study for biogenic carbon storage in the residential building stock

The built environment is both a major source of greenhouse gas emissions and an important area for climate mitigation through material choices, design and long-term use. Wood products can reduce emissions by substituting more carbon-intensive construction materials while also storing biogenic carbon in buildings. However, these benefits depend on how long buildings remain in use and how much carbon they retain over time. This study examines residential buildings in Helsinki, Finland, to estimate observed stock survival, quantify cumulative biogenic carbon storage in the residential building stock, and compare the results with estimates based on replacement cycles and the Intergovernmental Panel on Climate Change’s (IPCC) default 35-year half-life for harvested wood products (HWP). Results indicate high residential stock survival, with 92% of floor area still in use from the earliest study periods (1921–39). Timber buildings account for 40% of total biogenic carbon storage, despite representing only 10% of the gross floor area (GFA). The existing stock stores an estimated 266–285 kt C compared with 123 kt C predicted by the IPCC’s default half-life estimation. The results show that the IPCC’s default decay assumption produces substantially lower estimates when applied to long-lived residential building components.

POLICY RELEVANCE

This study provides empirical evidence on the survival of residential buildings and the associated long-term storage of biogenic carbon in wood materials. Helsinki’s existing residential stock stores approximately 266–285 kt C, indicating that long-lived buildings form a relevant urban carbon stock. The results also show that residential building survival is shaped not only by materials but also by stable housing demand as well as by institutional factors such as planning regulations, zoning, renovation programmes and heritage protection. For policymakers, better empirical data on building survival and component replacement can improve assumptions used in whole-life carbon assessment and evaluations of wood use in construction. The comparison with the IPCC’s default 35-year half-life further shows the importance of distinguishing broad HWP accounting assumptions from the behaviour of long-lived wood products in residential buildings.