Substitution impacts of wood construction in the EU: connecting building level substitution to upstream wood flows

Abstract With energy system decarbonization, embodied greenhouse gas (GHG) emissions increasingly drive construction-sector climate impacts, spurring research on wood substitution. At the sectoral scale, substitution impacts have typically been assessed using two substitution modeling approaches: (i) component-level substitution, which traces wood flows from forests to intermediate construction products, while ignoring functional equivalence at the level of downstream building assemblies; and (ii) building-level substitution, which assesses the environmental consequences of changes in wood use at the level of end-use functions, while paying less emphasis on upstream wood flows. This study advances the building-level approach by allowing to link building-level substitution impacts to specific upstream wood flows (i.e., an integrated building-level approach), demonstrated through a European Union (EU) case study. The results show that the substitution impacts (GHG emissions avoided) are 70–84% lower under both the conventional and integrated building-level approaches than under the component-level approach. This is mostly because the building-level substitution attributes substitution impact only to the additional wood used in wood-frame buildings relative to reference concrete buildings (which also contain some wood), while the substitution impact estimated based on component-level substitution covers all wood use (compared to a hypothetical non-wood reference). By explicitly tracing multiple wood flows and linking them to substitution impacts, the integrated building-level approach further indicates that increased wood supply does not necessarily ensure greater fossil emission avoidance, as outcomes depend on both the magnitude of additional wood supply and the efficiency of wood use.