Time impact analysis step by step

Time impact analysis is the method most contracts expect for an extension of time request made during the project. It is impacted as-planned done properly: instead of the original baseline, the fragnet goes into the schedule update in force just before the event, so it starts from the real status of the job. This lesson walks through a TIA step by step and shows how to review one.

Learning outcomes

• Prepare a TIA in five steps.
• Choose the correct schedule update as the base.
• Build a fragnet with sourced durations and logic.
• Review a TIA for the common errors.

The lesson

Five steps

In AACE RP 29R-03 terms, a TIA is modelled, additive, multiple base: MIP 3.7, because each event is inserted into its own contemporaneous update [1]. Done at the time, it supports a prospective extension. Done afterwards for a series of events, it becomes a retrospective tool with the same mechanics.

Choosing the update

Use the last accepted update with a data date before the event started. That update reflects actual progress and the logic in force at the time. Using a later update builds the effect of the event into the base; using the original baseline turns the TIA back into impacted as-planned.

Building the fragnet

A fragnet is a small set of activities that represent the event: for example, an owner decision, a redesign, procurement, and the installation that follows. Every duration needs a source document, such as a quotation, a lead time or a productivity record. Every tie needs a logical reason. Keep the fragnet as small as the event allows; a fragnet that rebuilds half the schedule is hard to defend.

Reviewing a TIA

• Is the base update the right one, and was it accepted?
• Are fragnet durations sourced?
• Are the ties logical, or do they force the result?
• Was float on the affected path considered?
• Has the contractor's own concurrent delay been considered for the same period?

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.

Event E-05: upgraded dock levellers (PCO-004). To install them before commissioning, Halvorsen needed the owner's decision by October 29, 2027; the supplier quoted 8 weeks from order to delivery. The owner approved the upgrade on December 3, 2027: 35 days late. The owner's representative prepares the TIA herself (Figure 2).

View the data

Item	Value
Decision due	Oct 29, 2027
Decision made	Dec 3, 2027
Late decision	35 days
Supplier lead time (quotation)	8 weeks
Float on leveller path, Oct 31 update	17 days
Critical delay	18 days

She inserts the fragnet into the October 31 update, the last accepted update before the decision was due. The leveller path had 17 days of total float in that update. A 35-day late decision less 17 days of float gives 18 days of delay to commissioning start and, through it, to Ready-for-Takeover. Halvorsen's version had claimed 28 days because it used a 10-week lead time, inserted into the original baseline. The 18-day result is the compensable owner delay accepted in the final settlement.

Your move

If you are the owner

• Require a TIA with every extension request. Put it in the Supplementary Conditions.
• Respond within a set time. A request left undecided can become a constructive acceleration claim (lesson 13).
• Check the base update first. The wrong update decides the answer before the analysis starts.
• Run your own TIA for your own events. It shows you the cost of a late decision before you make it.

If you are the contractor

• Submit the TIA with the notice or soon after. Prospective requests are strongest.
• Use the update in force. Not the baseline, not a later update.
• Attach the sources. Quotes, lead times, RFIs.
• Show the float. Explain how much was used and why the rest is critical.

Common mistakes

1. Using the original baseline. That is impacted as-planned, not a TIA.
2. Unsupported lead times. A longer lead time inflates the result.
3. Forcing ties. Logic that exists only to drive the path.
4. Ignoring float. Float on the path absorbs part of the delay.
5. Owners sitting on requests. Delay in deciding is itself a risk.

Quick quiz

1. What base schedule does a TIA use?

   1. The original baseline
   2. The last accepted update before the event
   3. The as-built
   4. Any update

2. Which AACE MIP is time impact analysis?

   1. 3.2
   2. 3.5
   3. 3.7
   4. 3.9

3. What must every fragnet duration have?

   1. A round number
   2. A source document
   3. Owner approval
   4. A constraint

4. The leveller decision was 35 days late with 17 days of float. What was the critical delay?

   1. 17 days
   2. 18 days
   3. 28 days
   4. 35 days

5. Why did Halvorsen's TIA show 28 days?

   1. It used a 10-week lead time in the original baseline
   2. It ignored the decision
   3. It used the as-built
   4. It was correct

Show answers and explanations

1. B. The update in force just before the event.
2. C. Modelled, additive, multiple base.
3. B. Quotes, lead times or productivity records.
4. B. 35 − 17 = 18 days.
5. A. A longer lead time inserted into the baseline overstated the effect.

Key terms

Time impact analysis (TIA)

A modelled method that inserts a fragnet into the update in force before an event and measures the effect.

Data date

The date up to which progress in a schedule update is recorded.

Multiple base

Using a different contemporaneous update as the base for each event.

Extension of time

An adjustment to the Contract Time, recorded by Change Order.

Prospective analysis

Analysis done at the time to forecast an event's effect.

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. Canadian Construction Documents Committee, CCDC 2-2020 Stipulated Price Contract, GC 6.4 to 6.6 and Part 8. Clause content checked against a publicly posted tender copy; buy the form from CCDC.
4. BRC, Northgate fact sheet (fictional case study, v1, November 4, 2026).

Verified on November 9, 2026.

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