Adaptability of design out waste concept to minimise waste in modular construction: a qualitative delphi study

Purpose The Design Out Waste (DOW) concept focuses on minimising waste during the design phase of construction projects, while Modular Construction (MC), an Off-Site Construction (OSC) method, involves prefabricating modules for on-site assembly. Although prior studies have independently demonstrated the waste reduction potential of DOW and MC, existing literature largely treats these concepts in isolation and lacks a stage-wise integration of DOW principles within MC processes. Given the construction industry's extensive waste generation, integrating the DOW and MC is crucial. However, there is a dearth of research on combining these concepts for waste minimisation. Hence, this study aims to assess the adaptability of the DOW in MC to minimise construction waste. Design/methodology/approach This study follows a pragmatic philosophy, combining theory and empirical data to develop practical solutions. A qualitative approach was used, involving three rounds of semi-structured expert interviews through the Delphi technique, consisting of 38 interviews in total. The data were analysed using manual content analysis. Findings The findings reveal a structured alignment between DOW and MC, identifying five DOW principles, including waste-efficient procurement, material optimisation and OSC, which align with 6 MC stages. While no common barriers across all 6 MC stages for this integration were identified, using BIM as a coordination tool for DOW emerged as a common strategy for waste reduction in all MC stages. These findings demonstrate how design-led strategies can systematically reduce waste throughout MC processes. Originality/value This study develops a stage-wise DOW–MC integration framework that systematically embeds relevant DOW principles across 6 MC stages, moving beyond uniform application assumptions. It also identifies stage-specific barriers and corresponding mitigation strategies for DOW implementation within MC, validated through Delphi expert consensus. The proposed framework offers actionable guidance for the construction industry to integrate waste minimisation into early decision-making, while contributing to society by promoting environmental protection and public health through the structured reduction of construction waste.