This study applies the Forgotten Effects Theory (FET), a fuzzy-logic-based modelling framework, to analyse how construction life cycle processes generate direct and indirect pressures on multiple planetary boundaries. The approach captures multistage and nonlinear causal relationships derived from expert-based incidence matrices. Results show that mineral extraction, material distribution, and waste disposal strongly influence ocean acidification; construction operations and building use affect biosphere integrity; material production drives land-use change; and demolition contributes to climate change. The analysis revealed substantial hidden effects: the influence of mineral extraction on ocean acidification increased from 0.4 to 0.9 when material production was included as a mediator; the relationship between building use and biosphere integrity increased from 0 to 0.8 through indirect pathways; and the influence of demolition on climate change increased from 0 to 0.8 through waste-disposal mediation. A ±10% sensitivity analysis confirmed the stability of the main incidence hierarchy, with changes below 0.05 for the most relevant coefficients. These findings demonstrate that indirect (“forgotten”) effects can be as influential as direct impacts, significantly intensifying pressures across planetary boundaries. The construction sector is therefore characterised as a cumulative and interconnected system in which impacts propagate and reinforce each other across life cycle stages. These results highlight the limitations of silo-based environmental assessments and underscore the need for integrated, life cycle-oriented sustainability strategies. Policies prioritising upstream interventions, material efficiency and reduced demolition can generate broader systemic benefits. The study demonstrates the potential of FET as a transparent and reproducible modelling approach for linking local construction decisions with global environmental processes, supporting more integrated circular economy strategies and contributing to the achievement of Sustainable Development Goals 11, 12 and 13.
