Schedule analysis methods: a map for owners and contractors

Delay analysis has a vocabulary that can sound designed to confuse: impacted as-planned, collapsed as-built, windows, time impact analysis. Behind the labels sits a simple map. AACE International's Recommended Practice 29R-03 sorts the methods into families, and the SCL Protocol sets out how to choose. This lesson gives you that map, so you can read any expert report and ask the right questions.

Learning outcomes

• Describe the AACE RP 29R-03 taxonomy: observational and modelled, static and dynamic, additive and subtractive.
• Distinguish prospective from retrospective analysis.
• Match common method names to the taxonomy.
• Choose a method based on the records available and the question asked.

The lesson

Two big families

AACE RP 29R-03 divides forensic schedule analysis into observational methods, which examine schedules as they were and compare them, and modelled methods, which insert or remove delay events in a schedule model and let the software calculate the effect [1]. Observational methods split into static logic, which compares a fixed baseline with the as-built, and dynamic logic, which uses the contemporaneous updates. Modelled methods split into additive, which inserts delays into a schedule, and subtractive, which removes them from an as-built model.

The nine protocols

RP 29R-03 sets out nine method implementation protocols (MIPs), numbered 3.1 to 3.9. Common names map onto them roughly as follows:

Prospective or retrospective

A prospective analysis is done at the time, to forecast the effect of an event and agree an extension while the work goes on. A retrospective analysis is done afterwards, to explain what actually happened. The SCL Protocol favours dealing with time as the project proceeds, close to the event, and for analysis after the event it lists factors for choosing a method rather than naming one preferred method [2].

How to choose

The right method depends on the question (forecast or explain), the records (are there reliable updates?), the contract (some prescribe TIA), the size of the claim and the time available. A method that needs good monthly updates is the wrong choice on a project that never updated its schedule properly. Lessons 7 to 10 walk through the four methods used most often.

Northgate worked example

Northgate Distribution Centre (fictional) is a 12,000 m² tilt-up warehouse in Vaughan, Ontario, built by Halvorsen Builders Ltd. (fictional) under CCDC 2-2020, with Ridgeline Architects Inc. (fictional) as Consultant. See the Northgate fact sheet. This course follows one delay claim from first notice to settlement. Ready-for-Takeover (M9) was due Friday, January 14, 2028 and was reached on Tuesday, March 14, 2028: 60 calendar days late. All events, dates and amounts are illustrative.

Halvorsen's scheduler built Claim C-01 on an impacted as-planned analysis: she inserted the owner's events into the baseline and reported a 52-day owner delay. The owner's representative chose a windows analysis using the monthly updates instead, because Northgate had eleven accepted monthly updates in native P6 format. That choice is defensible: the records support a dynamic, observational method, and it captures Halvorsen's own delays, which an impacted as-planned model does not. Lessons 8 and 10 compare the two results.

Your move

If you are the owner

• Require monthly updates in native format. They make the strongest methods possible.
• Specify the method for extensions. Many owners require a TIA for each request.
• Ask which MIP an expert used. And why it suits the records.
• Test the method, not just the answer. A good method with bad inputs still fails.

If you are the contractor

• Request extensions prospectively. A TIA at the time is cheaper and stronger than a retrospective claim.
• Match the method to your records. If your updates are reliable, use them.
• Avoid methods that ignore your own delays. Reviewers will run the method that doesn't.
• Document assumptions. Every inserted fragnet or removed delay needs a source.

Common mistakes

1. Choosing the method that gives the biggest number. Reviewers notice.
2. Using impacted as-planned years after the event. It ignores what actually happened.
3. No native files. PDFs cannot be analysed.
4. Mixing methods without explanation. Consistency matters.
5. Treating software output as proof. The logic must be checked.

Quick quiz

1. What distinguishes observational from modelled methods?

   1. Observational methods use software; modelled do not
   2. Observational methods compare schedules as they were; modelled methods insert or remove events and recalculate
   3. They are the same
   4. Modelled methods are only for owners

2. Which method is modelled, additive, multiple base (MIP 3.7)?

   1. As-planned vs as-built
   2. Time impact analysis
   3. Collapsed as-built
   4. Windows using updates

3. What does the SCL Protocol (2nd edition) say about retrospective methods?

   1. Always use TIA
   2. Lists factors for choosing rather than naming one preferred method
   3. Bans windows analysis
   4. Requires impacted as-planned

4. What is a prospective analysis?

   1. Analysis after completion
   2. Analysis at the time, forecasting an event's effect
   3. An audit of costs
   4. A cost estimate

5. Why did the owner's rep choose windows analysis at Northgate?

   1. It gives the smallest number
   2. There were eleven reliable native monthly updates
   3. The contract banned other methods
   4. Halvorsen asked for it

Show answers and explanations

1. B. That is the core RP 29R-03 split.
2. B. TIA inserts fragnets into successive updates.
3. B. The second edition moved away from a single preferred method.
4. B. Prospective analysis supports extensions during the work.
5. B. The records supported a dynamic, observational method.

Key terms

Forensic schedule analysis

The study of how events affected a project's timing, usually after the fact.

Observational method

Compares schedules as they existed, without inserting or removing events.

Modelled method

Inserts or removes delay events in a schedule model and recalculates.

MIP

Method implementation protocol: one of nine defined approaches in AACE RP 29R-03.

Fragnet

A fragment of network, a small set of activities representing a delay event.

References

1. AACE International, Recommended Practice No. 29R-03, Forensic Schedule Analysis, table of contents and method taxonomy (revision April 25, 2011).
2. Fenwick Elliott, The SCL Delay and Disruption Protocol: a second edition (November 2017), summarizing the Society of Construction Law Protocol, 2nd edition (February 2017).
3. Miller Thomson LLP, Ontario Court underlines the evidence and analysis required to establish critical path delays (July 2021).

Verified on November 9, 2026.

Next lesson in this trackAs-planned vs as-built analysis