AbstractThe designer competence is a key dimension in the prevention through design (PtD) practices that has yet to be explicitly highlighted and assessed in regards to its practical implications. Despite the subject of PtD in construction having been progressively studied, the context of the assessment of competence is virtually absent. At present, there is no index system that can represent the designer’s competence in PtD practice. To initiate the development of an index, this study adopted the Delphi method in order to obtain a consensus from 59 experts on the key attributes of the designer’s competence triangle (i.e., knowledge, skills, and experience) for PtD practice. The conceptual designer’s knowledge, skills, and experience index for PtD (KSEI-PtD) practice in construction was then developed based on the hierarchical ranking list of 18 key attributes and their relative weightings. The KSEI-PtD is a linear additive weighting model where its workability was demonstrated by integrating five competency levels and conducting case studies. The present study contributes to the body of knowledge by providing a method for the client, designer, or design organization to perform an initial assessment for designers’ PtD competence in construction. Additionally, the hierarchical ranking list of key attributes (KAs) of the designer competence triangle, its respective corresponding weights, and competency levels should enable key construction stakeholders to effectively prioritize their resources in ascertaining the required duties outlined in PtD-related legislative frameworks. The taxonomy measures and associated levels of the KSEI-PtD will be determined as part of future research, resulting in a fully working model needed to inform PtD competence-related policy and practice.