Construction Delay Analysis: Methods, Tools & Best Practices

Introduction

Delay analysis is the process of determining the causes, effects, and responsibility for schedule delays on a construction project. Multiple methodologies exist, each with different strengths, weaknesses, data requirements, and levels of defensibility. This guide compares all five major methods and provides a framework for choosing the right approach.

1. As-Planned vs As-Built

The simplest delay analysis method. It compares the original baseline schedule against the actual project timeline to identify variances. Activities that finished later than planned are flagged as delayed, and the analyst examines the causes.

Strengths: Simple to perform, requires minimal data (just baseline and as-built records), good for initial assessment.

Weaknesses: Does not use CPM logic, cannot identify which delays affected the critical path, cannot reliably handle concurrent delay, and ignores the dynamic nature of the schedule over time.

2. Impacted As-Planned

An additive method that inserts delay events into the original baseline schedule and recalculates the CPM to project the impact on the completion date. Each delay event is modeled as a fragnet and added to the baseline.

Strengths: Uses CPM logic, can quantify the impact of individual delay events, relatively straightforward.

Weaknesses: Assumes the baseline schedule is reliable and realistic, does not account for actual progress or critical path shifts that occurred during the project, may overestimate or underestimate impacts.

3. Collapsed As-Built

A subtractive method that starts with the as-built schedule and removes delay events to determine the “but-for” completion date — what would have happened without those delays. Also known as the “but-for” method.

Strengths: Works from actual data, useful when baseline schedule is unreliable or unavailable, can demonstrate the impact of specific delay events.

Weaknesses: Requires constructing an accurate as-built schedule, results can vary depending on the order events are removed, may not handle concurrent delays well.

4. Time Impact Analysis (TIA)

The most widely accepted modelled approach. Each delay event is modeled as a fragnet and inserted into the schedule at the point in time when the delay occurred. CPM is recalculated before and after insertion to measure the impact.

Strengths: Measures individual event impacts using the schedule as it existed at the time, accounts for the dynamic critical path, can identify concurrent delays.

Weaknesses: Requires detailed schedule updates and delay event documentation, more time-consuming than simpler methods.

5. Windows Analysis (MIP 3.7)

The most rigorous methodology. Divides the project into analysis windows (typically aligned with schedule update periods) and performs TIA within each window. Delay events are processed chronologically within each window, and the results are compared against actual progress.

Strengths: Most defensible method, captures all critical path shifts and concurrent delays, produces window-by-window and cumulative results.

Weaknesses: Requires the most data and effort, may be disproportionate for low-value disputes.

Decision Matrix

Conclusion

The choice of delay analysis method should be driven by the available data, the complexity of the dispute, and the level of rigor required. Where possible, use the most rigorous method the data supports. Constroma automates TIA and Windows Analysis, making the most defensible methods accessible without weeks of manual effort.