Mitigation and Acceleration: What’s the Difference and Why Does It Matter?
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September 19, 2025
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When construction projects experience delay and an extension of time is not feasible or is unwelcomed by the owner, the remedy seems to be simple: acceleration. Or is it mitigation? These two words are often used interchangeably in construction, but they are not exactly the same. This article will explore the difference between the two terms as described by industry schedule and cost control guidelines, how this is applied in contracts, and how the courts have ruled on claims for these costs.
What Does the Literature Say?
Acceleration is the execution of the contracted scope of work faster than originally planned. This may involve additional resources, additional shifts, or overtime work. AACE International (Association for the Advancement of Cost Engineering International) Recommended Practice 29R-03 defines two different types of acceleration: directed acceleration and constructive acceleration.
Directed acceleration: According to the AACE, directed acceleration occurs when the owner explicitly instructs the contractor to speed up work.1
Directed acceleration is generally compensable to the contractor, although the owner and the contractor may disagree on the associated costs.
Constructive acceleration: When the contractor makes the decision to speed up the execution of its work.2 According to the AACE, constructive acceleration occurs when five conditions are met:
- “The contractor is entitled to an excusable delay;
- The contractor requests and establishes entitlement to a time extension;
- The owner fails to grant a timely time extension;
- The owner or its agent specifically orders or clearly implies completion within a shorter time period that is associated with the requested time extensions; and
- The contractor provides notice to the owner or its agent that the contractor considers this action an acceleration order.”2
If the owner denies an extension of time claim, the contractor may still choose to implement constructive acceleration measures to meet project milestones and avoid penalties. If, at project completion, the contractor claims for the associated acceleration costs and a judge or arbitrator rules that the extension of time claim was justified, the contractor might recover its acceleration costs.
The contractor may also choose to accelerate voluntarily. For example, the contractor may choose to accelerate if it is behind schedule due to its own delays and wants to avoid penalties or simply wants to finish early. In both of these cases, the contractor is not entitled to recover the associated costs.
Mitigation is a measure taken by a contractor to reduce or eliminate the effect of delays already incurred or anticipated to occur. Mitigation efforts are usually associated with changes in the sequence of work and, as such, are considered to have minimal associated costs.
How Is This Applied Contracts?
Standard Canadian contracts often include language implying or explicitly requiring “each party to a contract to take action to decrease, lessen or minimize damages (time and money) to the other party.”3 The SCL International (Society of Construction Law International) limits the duty of the contractor to mitigate to the following:
This is because the claimant is generally not allowed to recover damages that could have reasonably been avoided.5
For directed and constructive acceleration, the costs of acceleration should be paid for by the party responsible for the delays that required the acceleration, or by the party that requested or planned the acceleration in the absence of delays. According to both the AACE and the ASCE (American Society of Civil Engineers), if the acceleration efforts were deployed as planned and the costs were incurred, these costs should be recoverable, regardless of whether the entirety of the planned acceleration was achieved.6,7
What Do the Courts Say?
In two hallmark court cases, namely Schindler Elevator Corporation v. Walsh Construction Company of Canada8 and Walsh Construction v. Toronto Transit Commission et al.,9 the courts placed a high importance on the ability of the contractor to demonstrate the costs incurred as a result of acceleration measures implemented. If the party seeking to recover costs cannot satisfactorily demonstrate these costs, as was the case in Schindler Elevator Corporation v. Walsh Construction Company of Canada,10 then these costs may not be granted, irrespective of entitlement.
What Does This Mean for You?
When a project experiences delay, regardless of the cause, the contractor has a duty to mitigate the effects of the delay, if it can do so without incurring significant costs. Once the opportunities for mitigation have been exhausted, the contractor should contemplate next steps. The contractor should notify the owner of the delay and request an extension of time.
This may lead to:
- The owner granting the time extension;
- The owner telling the contractor to accelerate; or
- The owner denying the extension, forcing constructive acceleration.
In all cases, the contractor’s decision to accelerate – and the associated costs – should be clearly communicated to the owner. If needed, the contractor should reserve its rights to claim for additional costs. Whether or not the parties agree to the cost of acceleration in advance, the contractor should maintain a clear record of acceleration costs, such as overtime, extra crews, weekend and night shifts, etc., to support or defend future claims.
Footnotes:
1: AACE International (2011). Recommended Practice No. 29R-03: Forensic Schedule Analysis.
2: AACE International (2011). Recommended Practice No. 29R-03: Forensic Schedule Analysis.
3: AACE International (2011). Recommended Practice No. 10S-90: Cost Engineering Terminology.
4: SCL Delay and Disruption Protocol 2nd Edition: February 2017.
5: ASCE (2016). Construction Contract Claims, Changes and Dispute Resolution. Third edition.
6: ASCE (2016). Construction Contract Claims, Changes and Dispute Resolution. Third edition.
7: AACE International (2011). Recommended Practice No. 29R-03: Forensic Schedule Analysis.
8: Schindler Elevator Corporation v. Walsh Construction Company of Canada, 2021 ONSC 283 (CanLII) retrieved on 2025-05-22.
9: Walsh Construction v. Toronto Transit Commission et al., 2024 ONSC 2782 (CanLII) retrieved on 2025-05-22.
10: Schindler Elevator Corporation v. Walsh Construction Company of Canada, 2021 ONSC 283 (CanLII) retrieved on 2025-05-22.
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