Screening the Import Exposure of Embodied GHG Emissions to Support Sustainable Infrastructure Rehabilitation: An Input–Output Case Study of an Underground Car Park in Madrid

Extending the service life of existing infrastructure is central to sustainable construction, but the embodied greenhouse gas (GHG) emissions of rehabilitation projects, and the share tied to imported supply chains, are rarely screened reliably because bills of quantities (BOQs) are heterogeneous and product-specific data are incomplete. This study screens both for the EUR 9.09 million rehabilitation of the Montalbán underground car park (Madrid) using environmentally extended input–output analysis. The 621 BOQ items were mapped to Spain’s 2022 input–output tables at basic prices, with final demand split into domestic and imported products; the domestic and total Leontief inverses separate domestic emissions from an import-exposure indicator under the domestic technology assumption (DTA). In the reference scenario, which removes the overlap between construction services and itemized materials, the footprint is 3325 tCO2eq (399 kgCO2eq/m2 of gross area; Monte Carlo 5th–95th percentiles 3058–3967 tCO2eq), of which 36.5% is import-exposed (35.6–36.5% across the four scenarios). Non-metallic mineral products account for 43% and seven components for 48%; a multiregional check suggests that the DTA understates import-related emissions by a factor of about 1.8. Based only on public statistics and the budget, the procedure gives contracting authorities a low-cost tool to target product-level data and sustainable public procurement.