The use of critical path analysis techniques in proof of delay claims is a relatively recent innovation. The use of these techniques in relation to the demonstration and proof of delay claims and the issues associated therewith is still a developing area of the common law. Part of this development has arisen from the need for courts (and other tribunals) to adapt to the new techniques made so accessible by computer. However, few cases have dwelt upon the use of the techniques used to demonstrate delay and their usefulness in making a successful claim at law.

This is almost certainly because, until relatively recently, the standard forms of contract almost invariably included arbitration clauses, which meant that disputes about delay claims would be referred to arbitration and, in most cases, the dispute thereby resolved. Since May 1, 1998, however, when the Housing Grants, Construction and Regeneration Act 1996 (''the 1996 Act'') came into force, the majority of delay claims have been resolved by adjudication.

Although the recent cases concerning delay analysis cover a variety of issues relevant to delay analysis, this article focuses primarily on the extent to which the English common law assists in addressing the central question: ''By what means does the contractor go about proving that the delays complained of will, or have, affected the completion date in a manner which is persuasive and yet proportionate to the matter in dispute?''⁵ In so doing, this article will seek to examine the approaches to delay claims which appear to have found approval with the courts and those which have not. First, however, the authors will briefly consider the contractual mechanisms in some of the commonly used standard forms of contract, which provide the contractual basis for claims for delay and which give rise to some of the issues examined later in this article.

Extension of time provisions in some of the standard forms of contract

Before one considers whether delay analysis is necessary, or which particular method is appropriate, the first thing that has to be done is to look at the contract. This is clearly a vital yet sometimes overlooked step. As often explained, an extension of time provision is a purely contractual mechanism designed to preserve the employer's entitlement to liquidated damages and to provide some additional allocation of risk in order to provide for ways in which certain foreseeable types of delaying event are to be dealt with in the event that they arise. There is nevertheless likely to be a close connection between making a claim for delay and recovering the additional costs incurred by the contractor associated with that delay. Delay claims are therefore of considerable commercial importance to contractors.

The standard JCT form of building contract 1998 edition (''JCT 98'')

JCT 98 is administered by an architect, who is appointed by the employer and acts as his agent, but is required to act fairly and reasonably towards the contractor when exercising his or her powers and duties under the contract. Extensions of time are dealt with under this form of contract at cl.25. Clause 25.4 provides a list of 18 categories of delay, which are known as ''relevant events'' that give rise to an entitlement to apply for an extension of time in the event that they occur. The principal steps leading to an extension of time as set out in the clause are as follows:

• When it becomes apparent that the progress of the works is being or is likely to be delayed then the contractor shall notify the architect of the cause of delay and identify whether in his opinion it is a relevant event.
  
  
• The contractor is required to provide with the notice, or as soon as possible after the notice, particulars of the expected effects of the event and an estimate if any of the expected delay to the completion of the works beyond the completion date.
  
  
• Upon receipt of the notice and any further particulars the architect is required to decide whether in his opinion any of the events notified are Relevant events and whether as a result of such events the works are likely to be delayed beyond the completion date. If he so decides, he is then required to give an extension of time to the contractor in writing as he then estimates to be fair and reasonable.
  

It is worth here emphasising the nature of the obligation on the part of the architect, since this is considered later in this article. The architect is required to apply some degree of discretion in deciding what is ''fair and reasonable''. In addition, it is not a condition of the entitlement to an extension of time that the event has caused delay to the ''Completion Date''. It merely requires the architect to form the opinion that as a consequence of the event ''the completion of the Works is likely to be delayed thereby beyond the Completion Date''.

This whole procedure is quite clearly intended to be carried out before the completion date since reference is made to the contractor notifying the expected effect of the event, not necessarily the actual effect of the event. The architect is then required to make a fair and reasonable estimate of the likely effect on the completion date, not wait until the completion date has arisen to determine the precise effect.

In practice, it is quite often the case that the architect will wait for full particulars of the actual effect of the event before making a decision, by which time the event and its consequences may be long past and the actual effect may be measured with greater certainty. It is quite common for architects to wait until after completion before making such grants of extension of time, but this is clearly not what the clause intended. The probable reason for this is that, once granted, an extension of time cannot be taken away unless works are omitted from the contract sum and it is fair and reasonable to reduce the time for completion of the works as a consequence of the omission. This almost certainly leads architects to err on the side of caution by avoiding awarding the contractor too much time.

There is in addition a 12-week review period which commences upon practical completion of the works in which the architect is required to review the extensions of time granted to the contractor and take account of any other relevant events that he is aware of, whether or not they have been notified by the contractor. Earlier extensions cannot be reduced unless critical works have been omitted since the previous extension of time. In accordance with cl.25.3.3.1, the architect is required to

'' fix a Completion Date later than that previously fixed if in his opinion the fixing of such later Completion Date is fair and reasonable having regard to any of the Relevant Events... ''.

• If one of the listed types of delay occurs, then within 28 days after the cause of delay has arisen or as soon thereafter as is reasonable deliver to the engineer full and detailed particulars in justification of the period of extension claimed in order that the claim may be investigated at the time (cl.44(1)).




• The engineer is then required to make an assessment of the delay, having regard to all the circumstances known to him at the time, whether or not the contractor has made a claim (cl.44(2)).





• If the engineer considers that the delays suffered fairly entitle the contractor to an extension of the time for substantial completion of the works then he grants the extension to the contractor in writing (cl.44(3)).
  
  

• Not later than 14 days after the due date or extended date for completion, the engineer is then required to make a further interim assessment based on all the circumstances known to him at the time and whether or not the contractor has made a claim (cl.44(4)).

• The project manager may notify the contractor of a compensation event at the time of the event, where the event arises from the project manager, and request the contractor to provide a quotation for the compensation event.
• The contractor otherwise notifies the project manager of any compensation event which has happened, or which he expects to happen, within two weeks of becoming aware of any such event.
• In order for the prices and/or the completion date to be changed, the project manager must decide that the event has not arisen from any default of the contractor, that it is a compensation event, and that it will have an effect on actual cost or completion, in which case he requests the contractor to submit a quotation.
• The contractor's quotation is required to include an assessment by the contractor of any proposed changes to the prices and any delay to the completion date as a result of the event. If the programme for the remaining work is affected by the compensation event, the contractor is required to include a revised programme showing the effect.
• The project manager may accept the quotation, request the contractor to submit a revised quotation or carry out his own assessment.
• A delay to the completion date is assessed by the project manager as the length of time that, owing to the compensation event, planned completion is later than planned completion shown on the accepted programme.
• A compensation event is implemented when the project manager accepts the quotation from the contractor or provides him with his own assessment.
• An assessment of a compensation event may not subsequently be revised if a forecast upon which it was based is later shown to be wrong, unless the project manager decides that the effects of an event are too uncertain to be forecast reasonably, in which case he states the assumptions on which the quotation and the assessment is to be based. If his assumptions are later found to be wrong, the project manager may notify a correction.

''In the context of the power to review it was contended that on a proper construction of clause 25.3.3, the power to review could only be exercised to grant the new completion date at a future date. Mr Justice Colman rejected this proposition, and held that the duty was to review the net extension to which the contractor was due, and that this could in many instances result in the completion date being fixed at a date prior to the date on which the review had taken place.''

''The dominant cause approach is supported as indicated above by authority of great weight in insurance cases. It is thought that the principles, so far as they apply, apply to contracts generally. It is accordingly submitted that the dominant cause approach is or should be the correct approach, as the law now stands, for Case C and for case B also, unless exceptionally the contract on its true construction provides an explicit answer without sophisticated analysis.''⁹

'' 'Dominant' has a number of meanings: 'Ruling, prevailing, most influential.' On the assumption that condition 23 is not solely concerned with liquidated or ascertained damages but also triggers and conditions a right for a contractor to recover direct loss and expense where applicable under condition 24 then an architect and in his turn and arbitrator has the task of allocating, when the facts require it, the extension of time to the various heads. I do not consider that the dominant test is correct. But I have held earlier in this judgement that the assumption is false. I think the proper course here is to order that this part of the interim award should be remitted to Mr Alexander for his reconsideration . . . .''

'' . . . it is agreed that if there are two concurrent causes of delay, one of which is a Relevant Event, and the other is not, then the contractor is entitled to an extension of time for the period of delay caused by the Relevant Event notwithstanding the concurrent effect of the other event. Thus, to take a simple example, if no work is possible on the site for a week not only because of exceptionally inclement weather (a Relevant Event), but also because the contractor has a shortage of labour (not a Relevant Event), and if the failure to work during that week is likely to delay the Works beyond the Completion Date by one week, and if he considers it fair and reasonable to do so, the Architect is required to grant an extension of time of one week. He cannot refuse to do so on the grounds that the delay would have occurred in any event by reason of the shortage of labour.''¹⁶

''However, if Taylor Woodrow was delayed in completing the works both by matters for which it bore the contractual risk and by Relevant Events, within the meaning of that term in the Standard Form, in light of the authorities to which I have referred, it would be entitled to extensions of time by reason of the occurrence of the Relevant Events notwithstanding its own defaults.''

''The law
[559] The law relating to extensions of time as a result of delay by the employer has been clarified in two cases-Balfour Beatty Building Ltd v Chestermount Properties (1993) 32 ConLR 139.

[560] The basic principle is encapsulated in para 12 of Dyson J's judgment in Henry Boot (70 ConLR 32 at 37):


'First, it is agreed that the analysis of Colman J in Balfour Beatty Building Ltd v Chestermount Properties (1993) 32 Con LR 139, should be applied. In his valuable interpretation of cl 25 of this form of contract, Colman J said, inter alia, that the purpose of the power to grant an extension of time under cl 25.3 was to fix the period of time by which the period of time available for completion ought to be extended having regard to the incidence of the relevant events, measured by the standard of what is fair and reasonable. The completion date as adjusted was not the date by which the contractor ought to have achieved practical completion, but the end of the total number of working days starting from the date of possession within which the contractor ought fairly and reasonably to have completed the works.'

[561] In Henry Boot, Dyson J dealt with the questions of concurrent delays and whether it is permissible to consider other events. In relation to the first question Dyson J said, at para 13 of his judgment (70 ConLR 32 at 37):


'Second, it is agreed that if there are two concurrent causes of delay, one of which is a relevant event, and the other is not, then the contractor is entitled to an extension of time for the period of delay caused by the relevant event notwithstanding the concurrent effect of the other event. Thus, to take a simple example, if no work is possible on a site for a week not only because of exceptionally inclement weather (a relevant event), but also because the contractor has a shortage of labour (not a relevant event), and if the failure to work during that week is likely to delay the works beyond completion date by one week, then if he considers it fair and reasonable to do so, the architect is required to grant an extension of time of one week. He cannot refuse to do so on the grounds that the delay would have occurred in any event by reason of the shortage of labour.'

In relation to the second question, Dyson J held that an architect is not precluded from considering the effect of other events when determining whether a relevant event is likely to cause delay to the works beyond completion.

[562] In the course of Mr Pye's evidence I made a number of rather off the cuff observations in relation to the causes of delay. I am satisfied that my approach must be that outlined in the passages from the judgment in the Henry Boot case which I have set out above. Crucial questions are (a) is the delay in the critical path and, if so, (b) is it caused by MBST? If the answer to the first question is 'Yes' and the second question is 'No' then I must assess how many additional working days should be included. If the alleged delay was caused by the default of MBST then they are not entitled to any extension of time.

[563] Other delays caused by MBST (if proved) are not relevant since the overall time allowed for under the contract may well include the need to carry out remedial works or other contingencies. These are not relevant events since the court is concerned with considering extensions of time within which the contract must be completed.

[564] I add that the approach must always be tested against an overall requirement that the result accords with common sense and fairness.'' (emphasis added)

This approach to dealing with loss and expense in relation to concurrent delay has found support from Lord Drummond Young in the Scottish Inner House Court of Session case of John Doyle Construction Ltd v Laing Management (Scotland) Ltd (2004). Paragraphs [10] to [20] of the judgment consider the question of ''causation of loss and global claims'', paras [14] to [17] in particular dealing with causation and the apportionment of loss in various circumstances, including situations of concurrent delay. Relevant extracts are as follows:

''[14]... In the first place, it may be possible to identify a causal link between particular events for which the employer is responsible and individual items of loss. On occasion that may be possible where it can be established that a group of events for which the employer is responsible are causally linked with a group of heads, provided that loss has no other significant cause. In determining what it is a significant cause, the 'dominant cause' approach described in the following paragraph is of relevance...



[15] . . . In the second place, the question of causation must be treated by 'the application of common sense to the logical principles of causation' ... In this connection, it is frequently possible to say that an item of loss has been caused by a particular event notwithstanding that other events played a part in its occurrence. In such cases, if an event or events for which the employer is responsible can be described as the dominant cause of an item of loss, that will be sufficient to establish liability, notwithstanding the existence of other causes that are to some degree at least concurrent . . .

[16] In the third place, even if it cannot be said that events for which the employer is responsible are the dominant cause of the loss, it may be possible to apportion the loss between the causes for which the employer is responsible and other causes. In such a case it is obviously necessary that the event or events for which the employer is responsible should be a material cause of the loss. Provided that condition is met, however, we are of opinion that apportionment of loss between the different causes is possible in an appropriate case. Such a procedure may be appropriate in a case where the causes of the loss are truly concurrent, in the sense that both operate together at the same time to produce a single consequence. For example, work on a construction project might be held up for a period owing to the late provision of information by the architect, but during that period bad weather might have prevented work for part of the time. In such a case responsibility for the loss can be apportioned between the two causes, according to their relative significance. Where the consequence is delay as against disruption, that can be done fairly readily on the basis of the time during which each of the causes was operative. During the period when both operated, we are of opinion that each should normally be treated as contributing to the loss, with the result that the employer is responsible for only part of the delay during that period. Unless there are special reasons to the contrary, responsibility during that period should probably be divided on an equal basis, at least where the concurrent cause is not the contractor's responsibility. Where it is his responsibility, however, it may be appropriate to deny him any recovery for the period of delay during which he is in default.''

This has a very important bearing on how delay claims and the resultant costs are analysed. For the purpose of determining the contractor's entitlement to loss and expense, it is necessary to distinguish periods of delay where the employer's action is the sole (or dominant) cause of the delay from those where there is a concurrent default on the part of the contractor.

It is important to emphasise the distinction between a matter which would entitle the contractor to an extension of time under the contract, such as a relevant event in accordance with JCT 98, from a matter which actually causes delay to completion of the work. For example, it is tempting for a contractor to argue that information issued late by the architect, relative to the information release schedule, notwithstanding the general progress on site, will be a concurrent delay for which the contractor should receive an extension of time. The contractor will only be entitled to an extension of time where the event affects the completion date, and only to the extent that it causes incremental delay to the completion date, rather than to the extent by which information is late relative to the information release schedule. This point was emphasised in the Brompton case.²⁰

There is then a clear distinction between concurrent cause and concurrent effect. Indeed, it is noted that this distinction is recognised in the extension of time provisions (cl.12) in the JCT Major Projects Form of contract, which specifically provides for the entitlement of the contractor to an extension of time notwithstanding the fact that there may have been a ''concurrent in effect of a cause'' for which there is no entitlement to an extension of time, i.e. the contractor's own culpable delay.

A resource-based quantification of delay

Construction projects are invariably highly labour-intensive, and so when one is looking to establish a measure of delay and its effect, one is almost certainly involved in considering the availability of resources to cope with additional or changed work and the effect of such changes on that resource. In the absence of very clear records, it may be necessary to make an approximation of the impact of delay on the available resources. Here lies a danger. If one takes, by way of an example, a variation for some additional joinery work which occupies two joiners for one week, then the delay to those two joiners is one week. If the particular work they are engaged in happens to be entirely critical then this would equate to a critical delay of one week to the completion date. But what happens if the work is not obviously critical but simply represents an increase in scope of work for that particular trade? The first point is that one has to demonstrate that this particular trade was critical at the time of the event. One then has to establish a measure of extent of the effect of that particular delay on the critical path.

It is not unusual for those who are involved in making claims for delay to inflate the claim by overstating the effect of an event by equating the effect of the delay to the specific resources engaged in the additional work rather than the effect on all the resources engaged in that particular trade at that point in time. This was precisely the manner in which the expert witness for the claimant approached the quantification of delay in the case of McAlpine Humberoak Ltd v McDermott International Inc (No.2),²¹ in which Lloyd L.J. stated as follows:

'' . . . he went through each of the VOs, and arrived at a number of days or weeks, based either on the time actually taken to carry out the extra work or on a calculation . . .

With perfect logic, he added a claim for night working, for his method of calculation assumed the same work force working one night shift throughout, as originally planned without any night shift . . .

One cannot help admiring the way in which [the expert witness] set about his task. It may be that there was no other way in which it could have been done. But it suffers from two major defects. So far as the first stage of calculation is concerned, [the expert's] approach assumed that if one man was working for one day on a particular VO, the whole contract was held up for that day. The point can be illustrated by VO 64, described by [D's counsel] as the reductio ad absurdum of [the expert's] method. The claim was for £39, being the cost of an inspector carrying out a lamination check on one of the secondary tees on W3. The inspection was carried out on 12 May 1982. It took no more than an hour. Yet [the expert] has allowed the whole day's delay to the whole of the work.

The second, and even more serious defect relates to the second stage of the calculation. It assumes that the whole of the workforce planned for a particular activity was engaged continuously on that activity from the day it started to the day it finished. This was hardly likely to be so, quite apart from the labour difficulties which the plaintiff suffered in phases 2 and 3 of the contract and the decision by the plaintiff towards the end of the contract to run down the labour force.''

''[The expert's] second main technique was to translate cumulative hours recorded on daywork sheets as spent on salt washing or mud clearing into equivalent working days and to treat those as further justification for attributing that part of the days lost to water ingress. Again, however, that conclusion simply does not follow. First, the labourers involved in those activities were only a part, and usually a small part, of the work force, the rest of which was not necessarily idle (and indeed, so far as the records have been examined with this point in mind, was usually not so in fact), so even in purely arithmetical terms and logic is flawed if an hour spent by, say, one or two labourers is equated with an hour lost to the whole project. Second, time lost in this way could in principle be made up by late working (as, again, often seems to have happened in practice). Third, it is wrong in principle to 'carry forward' a part day if the next element on the critical path is a concrete pour. A pour, once embarked upon, must be completed before the end the working day. Either it is commenced on the due date, however late, and completed, or it has to be postponed by a complete day or days; there simply cannot be a part-day loss on that score to be added to other part days.''

''When the defendant's witnesses came to give evidence, they undertook the task which was never undertaken by the plaintiff, of tracing the impact of every drawing revision, VO and TQ. . . The judge [at first instance] dismissed the defendants' approach to the case as being 'a retrospective and dissectional reconstruction by expert evidence of events almost day by day, drawing by drawing, TQ by TQ and weld procedure by weld procedure, designed to show that the spate of additional drawings which descended on McAlpine virtually from the start of the work really had little retarding or disruptive effect on its progress'. In our view the defendants' approach is just what the case required.''²⁴

''The respondent was entitled to respond to the claim both by arguing that the variations, late information and so on relied on by the claimant did not cause any delay because they were not on the critical path and positively by arguing that the true cause of delay was other matters''.

''Crucial questions are (a) is the delay in the critical path and, if so, (b) is it caused by MBST? If the answer to the first question if 'Yes' and the second question is 'No' then I must assess how many additional working days should be included.''

''It is Ascon which is seeking an extension of time and must establish a cause of a quantified period of delay entitling it to that extension''.

''It seems to me that it is a question of fact in any given case whether a Relevant Event has caused or is likely to cause delay to the Works beyond the Completion Date... ''.

''If it [adjudication] is to be utilised effectively, it is essential that the referring party gives the adjudicator all that is needed in a highly manageable form. From the material available to me, it is clear that BB did little or nothing to present its case in a logical or methodical way. Despite the fact that the dispute concerned a multi-million pound refurbishment contract, no attempt was made to provide any critical path. The work itself was no more complex than many other projects where a CPN [critical path network] is routinely established and maintained. It seems that BB had not prepared or maintained a proper programme during the execution of the works. By now, one would have thought that it was well understood that, on a contract of this kind, in order to attack, on the facts, a clause 24 certificate for non-completion (or an extension of time determined under clause 25), the foundation must be the original programme (if capable of justification and substantiation to show its validity and reliability as a contractual starting point) and its success will similarly depend on the soundness of its revisions on the occurrence of every event, so as to be able to provide a satisfactory and convincing demonstration of cause and effect. A valid critical path (or paths) has to be established both initially and at every later material point since it (or they) will almost certainly change. Some means has also to be established for demonstrating the effect of concurrent or parallel delays or other matters for which the employer will not be responsible under the contract.''

'' . . . indeed, there are those who'd say that the real point behind the case is that in practice Mr Recorder Toulson was calling for all significant extension of time assessments to be done by some CPM method, which seems to have some difficulties associated with it.

One point is that there are lots of rather modest disputes in which the cost of that approach would simply be not worth it.

Secondly, there are several forms of contract which seem to be less than wholly amenable to such methods. One takes the JCT Standard Form, they have as I've suggested, in some places built into them, apparently something in the nature of a discretion on the part of architect; that is to say that once he's undertaken whatever analysis and research he needs to get a view of the extensions of time and the incidence of delay, he then applies what I have called a discretion, which is no more and no less than asking himself a question, it is fair and reasonable that there should be an extension of time in these circumstances? Where you have a contract written in that way, and there are many of them, it seems that by and large, the final answer on extension of time is not one which can logically be developed by the use of computer program software and can only in the end be resolved by the exercise of some sort of discretion.''

''In the context of a dispute about the time for completion a logical analysis includes the logic required for in the establishment of a CPN [critical path network]''.

''it was plain from the evidence called at the sub-trial on behalf of the Claimant, in particular that of Mr. Gibson, who, of course is a programming expert, that there are a number of established ways in which a person who wishes to assess whether a particular event has or has not affected the progress of construction work can seek to do that. Because the construction of a modern building, other than one of the most basic type, involves the carrying out of a series of operations, some of which, possibly, can be undertaken at the same time as some of the others, but many of which can only be carried out in a sequence, it may well not be immediately obvious which operations impact upon which other operations. In order to make an assessment of whether a particular occurrence has affected the ultimate completion of the work, rather than just a particular operation it is desirable to consider what operations, at the time the event with one is concerned happens, are critical to the forward progress of the work as a whole. On the evidence of Mr. Gibson and Mr. Luder the establishment of the critical path of a particular construction project can itself be a difficult task if one does not know how the contractor planned the job. Not only that, but the critical path may well change during the course of the works, and almost certainly will do if the progress of the works is affected by some unforeseen event. Mr. Gibson frankly accepted that the various different methods of making an assessment of the impact of unforeseen occurrences upon the progress of construction works are likely to produce different results, perhaps dramatically different results. He also accepted that the accuracy of any of the methods in common use critically depends upon the quality of the information upon which the assessment exercise was based. All of this does, of course, emphasise the vital point that the duty of a professional man, generally stated, is not to be right, but to be careful.. . . His conduct has to be judged having regard to the information available to him, or which ought to have been available to him, at the time he gave his advice or made his decision or did whatever else it is that he did.''

''However, it is, I think, necessary to be clear what one means by events operating concurrently. It does not mean, in my judgment, a situation in which, work already being delayed, let it be supposed, because the contractor has had difficulty in obtaining sufficient labour, an event occurs which is a Relevant Event and which, had the contractor not been delayed, would have caused him to be delayed, but which in fact, by reason of the existing delay, made no difference. In such a situation although there is a Relevant Event,


'the completion of the Works is [not] likely to be delayed thereby beyond the Completion Date.'

The Relevant Event simply has no effect upon the completion date. This situation obviously needs to be distinguished from a situation in which, as it were, the works are proceeding in a regular fashion and on programme, when two things happen, either of which, had it happened on its own, would have caused delay, and one is a Relevant Event, while the other is not. In such circumstances there is a real concurrency of causes of the delay. It was circumstances such as these that Dyson J. was concerned with in the passage from his judgment in Henry Boot Construction (UK) Ltd v Malmaison Hotel (Manchester) Ltd at paragraph 13 on page 37...''