PurposeA challenge in implementing Universal Design (UD) is the perceived additional cost, which acts as a barrier to its widespread adoption. The few studies that have examined the cost for UD apply a theoretical research approach, failing to account for the unique design context that influences construction costs. This article presents a research methodology to calculate the UD cost in a realistic, context-dependent manner.Design/methodology/approachTo address this gap, “Research-by-Design” is applied in a case study approach involving twelve cases from three typologies: secondary schools, town halls and small retail shops. Two scenarios are compared to the existing situation: (1) “renovating into a 100% inclusive building” and (2) “building fully inclusive right away”.FindingsAlthough the methodology is time-consuming, it allows for a fair, realistic and detailed comparison between costs in different scenarios and cases. Findings show how financial implications are strongly related to its scale. Both “renovation” and “new build” scenarios involve costs, but these are considerably lower for the latter. “Circulation” and “Exterior stairs and ramps” are among the most expensive to renovate, but have almost no additional cost in the examined cases for the “new build scenario”.Research limitations/implicationsThe research methodology presented in this study is time-consuming, which may limit its feasibility for large-scale cost assessments in diverse contexts.Practical implicationsThe research methodology proposed in this study provides valuable insights for architects, designers and stakeholders involved in the implementation of UD. It offers a realistic and context-dependent approach to assess the cost implications of UD, enabling informed decision-making during the design and construction phases.Social implicationsBy revealing the specific cost implications of UD in different building contexts, this study contributes to promoting greater accessibility and inclusion in the built environment.Originality/valueThe applied approach distinguishes this study for its ability to provide rich contextual information on actual cost implications for UD. By considering real cases and their unique design contexts, valuable insights are offered into the true costs of implementing UD in the built environment.