Chapter 10: Acceleration

Who pays depends on what the extra spending was for. Finishing before the date the contractor owes is buying something new: an earlier date. Finishing before the late date the job is heading for is recovering delay, and then it matters whose delay it was. It also matters who decided to go faster. HHJ Hicks QC put the same two questions in Ascon v McAlpine (TCC, 1999). "Acceleration", he said, is not a term of art. To decide who pays, he asked "earlier than what?" and by whose decision the relevant steps were taken.

Acceleration is a kind of mitigation: making delay, disruption or their cost less severe. The Protocol calls it a subset of mitigation, typically where extra cost is spent to overcome delay or disruption. The link matters for the money, because the law of mitigation is where the damages route comes from.

Only work on the critical path is worth accelerating. The critical path is the longest chain of dependent activities through the job, and it fixes the finish date. Speeding up anything else only adds float to that activity and brings the finish no closer. Chapter 2 explains both ideas.

Even on the critical path, the return runs out. Shorten the critical chain enough and another chain becomes just as long. After that, more money on the first chain buys nothing. The model project shows it; it is invented and illustrative, with a planned finish in week 34 and a contract completion date in week 36. The roof design information arrives 4 weeks late, so roof design takes 8 weeks instead of 4. Forecast completion moves to week 37, a week past the completion date. The contractor puts extra labour on roofing and cuts it from 5 weeks to 3, and the job finishes in week 35. Cut roofing to 2 weeks, or to 1, and the finish stays in week 35. M&E design is now just as critical, and more roofers cannot touch it.

Returns also run out on site. Extra people in the same space get in each other's way. The Protocol's list of causes of lost productivity includes "crowding of labour or stacking of trades, dilution of supervision through fragmented work gangs, excessive overtime" (SCL 18.2). Night work has its own penalty. On the Shard frame the night shift had to keep the noise down, with restrictions on hammers. Steel members were often pinned together with one bolt until the day team finished the connections the next morning.

The Protocol accepts that acceleration can itself disrupt the work. If the measures are reasonable, though, that disruption ought to be offset by the overall delay recovery, unless other events intervene. Where the extra people crowd each other, the lost productivity may found a disruption claim of its own (SCL 16.6; chapter 11). A contractor that brings both claims must give credit in one for what it recovers in the other (SCL Part A, paragraph 9; chapter 13).

Pacing is the mirror image of acceleration: slowing non-critical work because the critical path is already late. Chapter 8 deals with it.

The contractor's promise is to finish by the completion date. How fast it works before then is its own affair. The Protocol notes that the method, speed and timing of the work are generally left to the contractor, subject to any process for accepting methods or programmes (SCL 15.6). So the employer has no general right to order the contractor to go faster. The Protocol draws the conclusion: the contractor cannot be instructed to accelerate to reduce Employer Delay, unless the contract allows for this. An employer that wants an earlier date must buy one, and the standard forms say how.

The JCT 2016 forms use an Acceleration Quotation. If the employer wishes to investigate completing before the Completion Date, the Architect/Contract Administrator (under Design and Build, the Employer) invites the contractor's proposals, priced and dated (SBC/Q 2016 Schedule 2, paragraph 2). The Design and Build form has the same machinery in Supplemental Provision 4, which applies unless the Contract Particulars disapply it. The contractor is under no obligation to accelerate until the employer confirms acceptance of its quotation. That does not affect its general obligations or its duty to proceed and complete (DB clauses 2.1 and 2.3). If the quotation is fairly prepared and not accepted, the contractor is paid a fair and reasonable amount for preparing it (SBC/Q Schedule 2, paragraph 5.2). The machinery buys a date earlier than the contractor already owes; it does not make the contractor absorb the employer's delay. JCT 2016 was officially withdrawn on 31 March 2026; check the 2024 edition's wording before relying on these paragraph numbers.

NEC4 works the same way. Either the Contractor or the Project Manager may propose to the other an acceleration to achieve Completion before the Completion Date (clause 36.1). The quotation is a change to the Prices plus a revised programme showing the earlier Completion Date (clause 36.2). If it is accepted, the Project Manager changes the Prices, the Completion Date and the Key Dates (clause 36.3). Nothing in clause 36 lets the Project Manager impose acceleration; it is a proposal either side may decline. Declining an acceleration quotation is expressly left out of the compensation event for withheld acceptances (clause 60.1(9)).

FIDIC's 2017 Red Book is different, and it deals with both kinds of lateness. Sometimes progress is too slow for reasons that give the Contractor no extension under Sub-Clause 8.5. The Engineer may then instruct it to submit a revised programme with the methods it proposes to speed things up. The Contractor adopts them at the Contractor's risk and cost, and pays the Employer's resulting costs on top of any Delay Damages (Sub-Clause 8.7). Where the delay comes from an 8.5 cause, acceleration measures the Engineer instructs are dealt with under the variation procedure in Sub-Clause 13.3.1 (Sub-Clause 8.7, last paragraph). So FIDIC lets the certifier order acceleration against delay for which the Contractor is entitled to an extension under 8.5, and deals with it through the variation procedure. These are the 2017 first-printing words; check the 2022 reprint before relying on them.

Two rules apply to acceleration that is instructed or agreed. The first is to fix the price before the work starts. Where the contract has no machinery but the parties agree to accelerate, the Protocol says to agree the payment and the records before the acceleration starts (SCL Core Principle 16). The second is that the contractor is paid for speed or for the extra time (prolongation), not both. Where acceleration is instructed or agreed, the contractor is not entitled to claim prolongation compensation for the employer delay the acceleration avoided. That delay never happened, because the acceleration the employer instructed or agreed to prevented it.

Asking is not ordering. Employers often ask a contractor in delay for a recovery programme. On the Protocol's approach, requiring the contractor to propose recovery measures is not an instruction or a deemed instruction to accelerate the works at the Employer's cost. Ascon points the same way. Acceleration not needed to meet the contractor's existing obligations is likely to result from an instruction the employer must pay for. But "pressure from the employer to make good delay caused by the contractor's own default is unlikely to be so construed" ([51]). Where the delay was the employer's and an extension was due, the answer depends on the contract and on what was said. Employers who want paid acceleration should say so and use the machinery. Employers who do not should say that too.

A contractor that recovers its own delay pays for it. It promised to finish by the completion date, and catching up is performing that promise. If it fails, it pays liquidated damages as well. FIDIC says so expressly in Sub-Clause 8.7. The JCT forms add a proviso that the contractor must constantly use his best endeavours to prevent delay in the progress of the works, "however caused" (DB 2016 clause 2.25.6.1). That is the best endeavours proviso.

Demanding payment to catch up your own delay can cost the contract. In Thomas Barnes (TCC, 2022) the contractor building Blackburn's bus station had fallen well behind. The judge found the further delay almost entirely the claimant's own fault and contractual responsibility. The contractor refused to commit to an accelerated programme without confirmation that it would be paid for it. The judge saw an unwillingness to take effective steps without first extracting a promise of payment to which it was not entitled ([201]).

By June 2015 the contractor had substantially suspended work until the Council agreed to a longer extension and a blank cheque to accelerate the works. The Council was entitled to terminate. It had under-granted the extension and had payment failings of its own, but none of that justified or excused the contractor's conduct ([216]). The case turns on the finding that the delay was the contractor's. It is not authority that a contractor must accelerate at its own cost against the employer's delay. Chapter 1 tells the whole story.

Employer delay is a different matter. The contract's answer to it is an extension of time. A contractor that takes the extra time is exactly where the contract meant it to be, and it has no reason to spend its own money handing back time the employer took. The Protocol agrees. Unless the contract or an agreement says otherwise, the duty to mitigate does not extend to requiring the Contractor to add extra resources or to work outside its planned working hours. If the employer wants those measures, it should agree to pay for them (SCL 15.5).

The general law points the same way. At common law, mitigation is not a duty owed to the other party. Leggatt J put it in Thai Airways (Commercial Court, 2015): mitigation is not in truth a duty but an assumption, unless the parties have agreed otherwise. Where a claimant has not acted reasonably, its damages are assessed as if it had. So it recovers nothing for loss it could reasonably have avoided. That limits what it recovers; it does not oblige it to accelerate.

Express terms can ask more, and the JCT proviso is the obvious one. The Protocol warns that "best endeavours" may place a higher burden on the Contractor than the normal duty to mitigate. Some forms go further and make compliance with a duty to reduce delay a condition precedent to recovering money or relief from liquidated damages (SCL 15.4). Chapter 4 deals with conditions precedent.

Where the delay comes from the other party's breach, the law of damages pays for reasonable attempts to reduce it. The principle is general. A claimant cannot recover for avoidable loss, but it can recover the cost of reasonable attempts to avoid loss (Thai Airways [32]). Leggatt J called the rules of mitigation aspects of causation. The breach caused the problem, so it caused the reasonable cost of dealing with it. Thai Airways was about late aircraft seats; its application to construction is by analogy. The Protocol applies the same idea: where the employer is responsible for the delay, the contractor may claim its acceleration costs from the Employer. "May" matters. The contractor still needs a breach, or a term of the contract, to claim under.

Cleveland Bridge v Severfield-Rowen (TCC, 2012) is the fullest English example. Cleveland Bridge fabricated and supplied the steel for the Shard, and delivered it late in breach of its contract with Severfield-Rowen (SRS), the steel erection subcontractor. SRS faced liquidated damages to the main contractor of £500,000 a week. Akenhead J held that SRS's recovery programme was sensible and reasonable mitigation, and that a concerted effort to work extra hours was at every level reasonable. Cleveland Bridge did not seriously argue otherwise.

The acceleration failed, and that did not matter. Other causes kept the frame late, but that failure can not and should not prevent or limit recovery of the reasonable costs. The reason is fairness about hindsight. Reasonableness is judged when the decision is taken, and the party in breach created the difficulty. The judge quoted Lord Macmillan's words in Banco de Portugal v Waterlow. The measures a claimant is driven to adopt "ought not [sic] be weighed in nice scales" by the party in breach (as quoted in Cleveland Bridge [142]).

Then came the limits, and they took most of the claim away. First, only the part of the acceleration aimed at the supplier's delay counted. When the recovery programme started in May 2010 the delay stood at 8 weeks, of which 6 were Cleveland Bridge's. So the acceleration costs were reduced by 25%, a discount both experts and counsel accepted ([143], [169]). Second, there was a tipping point. From the end of August 2010 other causes were the dominant reason for keeping the extra resources on, and their cost after that was not Cleveland Bridge's.

Third, SRS had to prove its costs. It got nothing for the extra shifts between February and May, because a nagging feeling that some were caused by the breach was not enough. The judge noted that representative evidence would have been easy to give. He also refused to take the total and cut it by a percentage, which would have been simply arbitrary. He worked from the recovery programme instead.

For the day and night shift squads SRS claimed £1,682,001.76. The judge allowed £522,659.05 ([170]), including overheads and profit for the erector, which had been asked to provide the extra resource. Supervisors brought £29,305.82 and senior management £29,594.21, each a reasoned share of their time. Specialist sub-subcontractors brought nothing, because SRS's own quantum expert was unable to say whether they had anything to do with acceleration. Chapter 12 returns to the same judgment for its disruption claim.

Proving that the delay caused the acceleration is not the end of it. The Protocol warns that the full costs of those measures were not necessarily caused by the employer delay. Its example is a second gang. Two gangs may finish sooner while using the same man-hours one gang would have used. Only the extra hours, and any higher rates the delay forced on the contractor, are the cost of speed. Take invented numbers. One gang for 7 weeks is 7 gang-weeks. Two gangs for 4 weeks is 8 gang-weeks. The cost of the acceleration is the eighth gang-week and any premium rates, not the whole of the second gang. The Protocol also suggests comparing that cost with the prolongation costs that would otherwise have arisen, to test whether it was reasonable (SCL 16.6).

A contractor cannot have the time and the cost of avoiding it as well. In Ascon a subcontractor claimed its acceleration costs as mitigation of delay caused by the main contractor. The judge doubted, without deciding, whether there was any room for the doctrine of mitigation where the contract deals with the other party's delay by extensions and loss and expense. He added that a contractor cannot have a full extension, with damages on that basis, and also its mitigation costs. The exception is where it pleads and proves that the acceleration, though reasonable, achieved nothing. The logic is causation again. Acceleration that worked removed some of the delay, so there is less delay to claim for. Ascon's own claim failed: the subcontractor said its acceleration had worked ([56], [59]).

Constructive acceleration is acceleration forced by a refused or late extension. In the Protocol's definition, the certifier fails to recognise an employer delay for which an extension is due. That failure required the Contractor to accelerate its progress to meet the existing completion date. The failure may come from the employer's denial of a valid request or the certifier's late grant. The same entry ends: this is rarely recognised under English law.

The idea comes from the United States. AACE's recommended practice on forensic schedule analysis says it generally occurs when five criteria are met (29R-03, s.4.4.A). The contractor is entitled to an excusable delay. It asks for an extension and shows its entitlement. The owner fails to grant it in time. The owner orders, or clearly implies, completion within the shorter time. And the contractor gives notice that it treats this as an order to accelerate. AACE, writing in 2011, called it not (currently) a recognized concept under English law. It relied on the 2002 SCL Protocol, which advised against making "a claim for so-called constructive acceleration" (SCL Protocol 1st edn, 2002, 1.18.5). The 2017 Protocol softened that to "rarely recognised". I know of no English decision that recognises constructive acceleration as a claim in its own right.

The reluctance follows from principle. First, acceleration is not a cause of action, so the contractor needs a breach or a term. A refusal to extend time does not, on its face, tell the contractor to go faster. Second, a wrong refusal is not final. The House of Lords described a certifier's certificates as having only a provisional validity. The certifier's decision can be reviewed, and either party can refer the dispute to adjudication, which must produce a decision within 28 days of referral unless the time is extended (Construction Act 1996, s.108(2)(c)). The law's answer to a wrong refusal is to correct the date. Once the date moves, the liquidated damages the contractor feared fall away. Third, a contractor that spends money to beat a date that is later moved has chosen to spend it. The question is still whether the employer's breach caused that cost.

The practical route is the one the Protocol recommends. Before accelerating, the contractor should first take steps to have the dispute or difference about entitlement to an EOT resolved under the contract's dispute provisions. It should give the certifier notice with particulars of the measures it intends, and put them in a revised programme (SCL 16.5). A contractor that accelerates to avoid liquidated damages without doing this will find its costs hard to recover. If it can, it should agree the price with the employer first. It should record who asked for the acceleration, when, and why. It should keep shift and gang records that tie each extra shift to the delay it is meant to recover. And, as Thomas Barnes shows, it should keep working while it argues.

The last point is a warning to employers. A variation instructed after the completion date, while the contractor is late through its own fault, can cost the employer its liquidated damages. The Protocol says the employer may lose its entitlement to liquidated damages if two things follow. The contractor accelerates at its own cost to recover its own delay. And the variation then becomes the effective cause of delay to completion.

The reason lies in two rules about culpable delay, meaning delay that is the contractor's responsibility. First, an extension for an employer event during culpable delay adds only the delay that event actually causes to the existing completion date. That is the net method, adopted in Balfour Beatty v Chestermount and restated in Walter Lilly (TCC, 2012), where Akenhead J recorded that the "net" method was correct. Second, on the Protocol's view, an employer event that arrives when the job is already going to finish later because of the contractor does not make it finish any later (SCL 10.9). On that view the variation sits in the shadow of the contractor's delay, and earns no extension. Chapter 8 explains why.

The shadow lasts only while the contractor stays late. Take invented numbers. The completion date is week 30, and the contractor's own delay means the job will finish in week 36. In week 31 the employer orders extra work, done alongside the contractor's late work, which will take until week 36. On the Protocol's view, and on Adyard's actual-delay approach, the variation changes nothing as things stand: the job was finishing in week 36 anyway. The contractor faces 6 weeks of liquidated damages. If the two delays are truly concurrent, English courts may extend time anyway (chapter 8). Now the contractor puts on a night shift, at its own cost, and finishes its own work in week 32. The job still cannot finish before week 36, because the extra work is not done. The variation is now the effective cause of the last 4 weeks. The contractor gets a 4-week extension, to week 34, and pays liquidated damages for 2 weeks instead of 6.

If the contract gives no extension for that variation, the result is worse. Under the prevention principle, as Jackson J put it in Multiplex (TCC, 2007), the employer "cannot insist upon the performance of an obligation which he has prevented" the contractor from performing ([47]). Where it applies, time is set at large and the liquidated damages clause falls away altogether. An act of prevention does not set time at large if the contract provides for an extension for it ([56]). In Adyard (Commercial Court, 2011) Hamblen J noted that otherwise a trivial variation may lead to the loss of the right to liquidated damages for a long period of culpable delay. He gave that as a reason for reading the contract so as to avoid the result.

That risk arises only where the variation actually delays completion and the contract gives no extension for it. The JCT clause considered in Walter Lilly does give an extension for a variation during culpable delay, calculated by the net method (chapter 3).

The practical lesson is about timing. Before instructing change after the completion date, an employer should ask three things. Can the change wait until the works are complete? Will it run alongside the contractor's late work, so that a recovery by the contractor would leave it exposed? And does the contract extend time for it? Chapter 9 deals with what happens to liquidated damages when time is at large.

Acceleration is priced with the other money claims in chapter 13, and the productivity it loses is measured in chapter 11. The records that prove both are in chapter 14.