A methodology for integrating toxic emission from building materials during the use stage into building life cycle assessment

Abstract Purpose This paper develops a reproducible calculation procedure to integrate human toxicity from construction material emissions during the use stage into building LCA, focusing on the indoor air emissions stage (module B1 under EN 15978). The research evaluates whether a building inventory (elements, materials and product documentation) can be translated into a substance‑resolved emission inventory by compartment (household indoor or outdoor) and subsequently characterised with USEtox, while preserving traceability and operability with commonly available data. Methods The method follows a four step workflow: (1) disaggregation of the building into Level(s) elements, materials and substances; (2) conversion of contained mass to cumulative B1 emissions through an explicit rules matrix (physicochemical class crossed with construction position) assigning indoor or outdoor compartments; (3) impact characterisation using USEtox compartment specific factors (CTUh and DALY); and (4) hierarchical aggregation (substance to material to element to building). Substances lacking a USEtox characterisation factor are retained as identified but assigned CF = 0, and coverage metrics are reported to delimit the evaluated fraction. The procedure is positioned as a screening and prioritisation tool rather than a predictive concentration model; its consistency is supported by bibliographic justification of the emission matrix, sensitivity analysis on key assumptions and benchmarking against published USEtox‑based and dynamic IAQ studies. Results and discussion Application to a two-storey detached house reveals two dominant patterns. First, impacts are concentrated almost entirely in the household indoor compartment, consistent with higher exposure potential under confined conditions. Second, results are highly concentrated in a small set of elements and materials (notably insulation, primers and sealants), while many elements remain at zero. This sparsity reflects both methodological filters (emission rules) and data constraints (compositional disaggregation and USEtox coverage). Therefore, “zero” contributions must be interpreted as an evaluation zone limited by data rather than intrinsic harmlessness. The findings highlight the structural gap between building scale decision making and the effective availability of characterisation factors at the substance scale, identifying where further chemical documentation is most critical. Conclusions A transparent, traceable bridge between building inventories and USEtox characterisation can be implemented for the indoor air emissions stage without dynamic IAQ modelling, enabling screening and comparative prioritisation during design and specification. Practical uptake depends more on chemical traceability and coverage than on model sophistication. The method contributes to integrating indoor‑related human health impacts alongside the other environmental categories covered in building LCA, supporting more health‑informed design and specification decisions.