Improving But-For Delay Analysis and Concurrency Assessment

But-For analysis is one of the popular techniques for apportioning the responsibility for project delays among the project parties (owner, contractor, and third party). Despite its acceptance by courts, one of its known drawbacks is that it produces conflicting results when adopting different party’s viewpoints. Moreover, But-For analysis is not able to identify the concurrent delays caused by multiple parties. Despite some literature modifications to address those shortcomings, Modified But-For (MBF) analysis persistently does not consider event chronology and thus can produce wrong results. This paper thus discusses the concurrency assessment method of the MBF and introduces implementation improvements to divide the analysis into multiple windows to increase the analysis resolution, account for critical path fluctuations, and consider the chronology of different-party events, which is a requirement by recent delay analysis guidelines of professional bodies such as AACE and ASCE. A case study is used to show a detailed procedure for applying multiple-window MBF analysis to produce more accurate and repeatable delay analysis, considering concurrent delays. © 2020 The Authors. Published by Budapest University of Technology and Economics & Diamond Congress Ltd Peer-review under responsibility of the Scientific Committee of the Creative Construction Conference 2020.