[2016] CSOH 98




In the cause






Pursuer:  Bowen QC, Broome;  Wright Johnston & Mackenzie LLP

Defender:  Murphy QC;  Pinsent Masons LLP

7 July 2016

[1]        The defender in this action was the main contractor for the construction of the SSE Hydro building in Glasgow.  The pursuer was engaged by the defender as sub‑contractor for work packages consisting, in general terms, of the structural steelwork, roof steelwork and roof cladding.  The present action has been raised to obtain a judicial determination of a number of issues in connection with claims by the pursuer for additional payments under the sub‑contract and for extension of time.  This is the third opinion I have delivered in the action, having addressed other issues in my opinions dated 19 June 2015 and 6 May 2016, published at [2015] CSOH 81 and [2016] CSOH 66 respectively.  The present opinion is concerned with three matters on which a diet of proof before answer was allowed. 

[2]        The proof was heard over seven days commencing on 26 April 2016.  Subject to my observations below regarding the pursuer’s operations director, Mr Hugo Camacho, I found all of the witnesses who gave evidence on factual matters to be credible and reliable.  Expert evidence was given on behalf of the pursuer by Mrs Lucy Osborne, a chartered civil engineer with experience of management of structural design teams and processes and, on behalf of the defender, by Mr Matthew Davis, a chartered civil and structural engineer with similarly extensive design and investigatory experience.  Both expert witnesses were well qualified to express opinions on the technical questions with which this case is concerned;  however, a number of the issues upon which they expressed views were properly matters for the court. 

[3]        In my opinion dated 19 June 2015, I described the construction process, in so far as material to the pursuer’s sub‑contract works, as follows:

“Those sub‑contract works consisted of five elements: main steelwork, bank roof steelwork, main roof steelwork, main roof covering, and lighting gantry.  The main steelwork consisted of the structural steel columns of the main walls.  An important feature of the construction sequence was that the steel columns were not erected from bottom to top at one time, but rather level by level.  Concrete fin walls were poured to a certain level and the pursuer then erected its steel columns to the same level.  After the construction of decking at that level, the sequence of concrete followed by steel columns was repeated to the next level, and so on.  This process was not, however, carried out for the whole building at once.  Instead, the ellipse was divided into 12 sectors, and the level by level sequence that I have already described was carried out sector by sector.  Due to the design of the building, the sectors were of differing heights, and consequently there were large variations in the sizes of the structural steel members.  Within each sector, and at each level, progress with the pursuer’s steelworks depended upon completion of the immediately preceding concrete works, and vice versa.


The sequence of construction of the main roof steelwork was similarly divided into segments, albeit 16 instead of the 12 external wall sectors.  In the centre of the roof was a circular steelwork structure held temporarily in place by a vertical propping tower.  Each segment of the roof steelwork was built out from the top of the external wall to join the circular central section.  Commencement of construction of each segment of the main roof steelwork was dependent upon completion of construction of the concrete and steelwork of the sector of the external wall from which it was built out.  Once the segments of roof steelwork had been connected to the circular central structure, the central support trestle was removed. “


An important feature of the building is that the external wall increases in height towards the rear of the auditorium, with the consequence that the domed roof is set at an angle to the ground.  The roof is circular in the plane of the ring beam that runs around the circumference of the dome.


The sub-contract agreement
[4]        The sub‑contract agreement was executed on behalf of the pursuer on or about 18 March 2011 (the copy lodged in court does not bear a date of signature) and on behalf of the defender on 8 June 2011.  The pursuer’s sub‑contract was for WP (ie work package) 2400 consisting of structural steelwork including metal decking and roofing.  The sub‑contract agreement incorporated the conditions of the GC/Works Sub‑Contract as amended by conditions set out in part 2 of a schedule to the sub‑contract agreement.  Article 1.5 of the sub‑contract agreement provided as follows:

“The Sub-Contract Works shall be completed in accordance with and the rights and duties of the Contractor and the Sub-Contractor shall be regulated by:


1.5.1    The Abstract of Particulars annexed in Part One of the Schedule and signed as relative hereto;


1.5.2    The Sub-Contract Conditions as amended by the conditions annexed in Part Two of the Schedule and signed as relative hereto;


1.5.3    The Sub-Contract Documents listed in Part Three of the Schedule

all of which are held to be incorporated in and form part of the Sub-Contract.”


I refer below to certain sub‑contract conditions and documents relevant to particular issues addressed during the proof; in addition, there are conditions of more general relevance to the question whether a particular direction has resulted in a variation, as follows.

[5]        Clause 1.3 of the GC/Works Sub‑Contract conditions contained definitions.  These include the following definition of a Variation:

“any alteration or addition to or omission from the Sub-Contract Works or any change in the design, quality or quantity of the Sub-Contract Works which is required by a direction of the Contractor issued under the Sub-Contract.”


[6]        Clause 4.3.1 stated:

“The Contractor may issue any reasonable direction in writing to the Sub-Contractor in regard to the Sub-Contract Works (including the ordering of any Variation therein).


[7]        Clause 13.3.1 stated:


“Where as a result of a direction of the Contractor, not being a direction requiring a Variation, the Sub-Contractor:


  1. properly and directly incurs any expense beyond that provided for in, or reasonably contemplated by the Sub-Contract; or


  2. makes any saving in the cost of executing the Sub-Contract Works,


the Sub-Contract Sum shall, except where the direction was necessary because of any default or neglect by the Sub-Contractor be increased by the amount of the expense, or decreased by the amount of the saving in either case as determined by the Contractor.”


Issue 1: ETFE secondary support system
[8]        The façade of the Hydro consists of pillow cladding made from ethylene tetrafluoroethylene (ETFE) in an aluminium frame.  The pillow cladding is supported by a secondary steel support structure which is attached in turn to the main steelwork and concrete frame of the building.  Design of both the ETFE cladding system and the secondary steel support structure was sub‑contracted by the defender to Novum Structures UK Limited (“Novum”).  The pursuer was responsible for the fabrication, delivery and installation of the secondary steel support structure.  Problems arose during construction regarding (a) the alignment of the secondary steel support structure with the main frame of the building, and (b) the alignment of the ETFE cladding with the secondary steel support structure.  Directions were issued to the pursuer, which now seeks declarator that each of these directions was a variation.


Sub-Contract Conditions
[9]        It is necessary to begin by identifying the terms on which the sub‑contract was entered into, so far as material to the ETFE cladding support system.  Prior to submission of its tender, the pursuer had received from the defender a set of drawings prepared by Arup, the project engineers, to provide an indication of the intended means of attachment of the cladding system to the frame of the building.  One revision of these drawings (T2) dated 23 November 2009 was prepared for the purposes of the ETFE competitive dialogue process and was issued “for information”.  A later revision (T7) dated 28 March 2010 was the contract tender issue.  These two versions differed in that the T2 drawings showed all of the six circular horizontal hollow steel tubes attached to the concrete and steel frame, whereas T7 showed only one horizontal tube.  It appears that the pursuer received both the T2 drawings and also the T7 tender drawings, but neither T2 nor T7 contained any detail to assist a tenderer for the fabrication of the secondary steel support structure other than the information that it would require to include circular hollow steel tubes to be attached to the main frame of the building.  On 20 May 2010, Mr Alister Aitken, the defender’s commercial manager, sent an email to the pursuer’s Mr Miguel Garces attaching “the best information we have in respect of the ETFE cladding rails to allow you to provide a price”.  This information consisted of a table received by the defender from Novum setting out in considerable detail the dimensions and weights of the various components of the secondary support system, including bracket tubes, bay tubes, verticals, bracket assemblies, tube end plates and “upstands”, ie brackets to be used for attachment of the ETFE cladding frame to the secondary support system.  No drawing accompanied the table sent by Mr Aitken to Mr Garces.

[10]      As well as tendering directly to the defender for fabrication and installation of the secondary support system, the pursuer also provided Novum with a price for supply of steelwork to enable Novum to submit a quotation to the defender for supply and installation of the entire cladding system including support steelwork.  In furtherance of that possible contractual arrangement, an email was sent on 1 June 2010 by Novum’s Tom Churchyard to the pursuer’s director Mr Hugo Camacho.  That email stated inter alia:  “Please find attached the information for pricing purposes for the [Hydro] project”.  The email chain lodged in process was accompanied by detailed drawings and computer-generated images showing the design of the bracket assemblies to be used to attach the circular hollow tubes to the building frame, as well as the upstands to be used to attach the ETFE cladding frame to the secondary support system.  Mr Churchyard did not give evidence and Mr Camacho could not confirm whether he had received these attachments or not.  His position was that they were in any event irrelevant as they were concerned with a potential contract to supply Novum, which did not happen, and not with the contract which was in fact entered into directly with the defender.

[11]      On 2 June 2010, the pursuer submitted Revision D of its tender to the defender;  the significance of Revision D is that the pricing schedule contained in that revision was subsequently included in the sub-contract documents.  As regards ETFE cladding rails, the pricing schedule included prices for supply and fabrication, “in accordance with the Engineer’s drawings and specification” of bay tubes, bracket tubes, vertical tubes, bracket plate assemblies and tube end plates.  The quantities of steel listed in the pricing schedule correspond very closely indeed with those set out in the table attached to the email sent by Mr Aitken to Mr Garces on 20 May 2010 and, in my assessment, the similarity leaves no room for any serious doubt that the information contained in that table was available to and used by the pursuer, along with the engineer’s T2 and/or T7 drawings, when submitting its tender Revision D.  I am also satisfied that the Novum drawings and images were available to the pursuer at the time when tender Revision D was submitted;  this follows from the fact that the pursuer appears to have been able to submit a quotation to Novum at about the same time.  Whether, and if so to what extent, the pursuer actually made use of the Novum drawings in pricing its tender to the defender is less clear, but I do not regard that as directly relevant to the question that I have to decide. 

[12]      In this context I have to comment on the evidence of Mr Camacho.  On the subject of the basis of the pursuer’s tender and pricing I found him somewhat evasive.  He appeared initially to assert that the only information available to and taken into account by the pursuer was that contained in the Arup drawings T2 and T7.  His position changed to being that the bill of quantities supplied by the defender to the pursuer for pricing already contained a list of component parts and quantities of steel required;  I do not accept that this was the case.  Eventually, having been referred to email correspondence in January 2011 which appeared to confirm that the pursuer had priced on the basis of the table attached to Mr Aitken’s email, he accepted that this was so.  In view of these inconsistencies as well as his reluctance to provide direct answers to questions as to the information used by the pursuer for pricing purposes, I did not find Mr Camacho to be a reliable witness and have approached his evidence on this chapter of the case with caution.


Instruction A2400/85
[13]      On 22 June 2011, the defender issued to the pursuer an instruction (to which I shall refer as Instruction 85) entitled “Novum drawings with comments for your information”.  The instruction stated:

“Please proceed with your Sub-Contract works in accordance with the attached construction issue design information.  Should you consider any of this information to constitute a variation under the terms and conditions of your Sub-Contract, you must notify us of this by return, and within 5 days of receipt of this instruction you must provide detailed substantiation of the cost and programming implications that you consider applicable for the work instructed for our assessment.  Failure to comply with this timescale may result in BLL rejecting any claims for additional costs or programme implications.”


The design information attached to this instruction consisted of drawings produced by Novum showing detail of steelwork rail, bracket and upstand principles at various locations.  The drawings show inter alia the bay tubes, bracket tubes and vertical tubes that comprise the elements of the hollow steel sections of the secondary support system, as well as the connections and bolt locations of those elements.

[14]      On 27 October 2011, the pursuer issued to the defender a document entitled “Variation no. 66” which noted, under the heading “Modification ETFE system”, that the ETFE system had undergone several modifications since the tender phase.  The pursuer presented a non-exhaustive list of points to be taken into consideration.  These included:

-           New design and modelling requirements from Martifer;


-           Due [to] the increase of details the fabrication drawings are now more complex to execute taking more time from the designing team;


-           Fabricate and install new embed details onto steelwork columns and concrete columns;


-           Fabricate and install new Brackets…;


-           Fabricate and install new Bracket Tubes…;

The increased value of this variation was calculated to be approximately £740,801.65 in total.  The claim was considered by Mr Nick Harty, the defender’s commercial manager.  Having consulted with Mr Aitken, Mr Harty carried out a comparison between, on the one hand, the pricing schedule, the table attached to Mr Aitken’s email of 20 May 2010, and the Novum drawings attached to Mr Churchyard’s email of 1 June 2010 and, on the other hand, the drawings attached to Instruction 85.  Mr Harty did not agree with the pursuer’s characterisation of the latter as a new design of the secondary support system.  He noted what he regarded as some minor changes to the detail of the design relating mainly to bolts and welding.  He valued these changes at £36,822, which sum was paid to the pursuer.  The remainder of the pursuer’s claim for a variation was rejected. 

[15]      In the course of preparation for this proof, Mr Aitken carried out a comparison between (i) the parts list in the table attached to his email of 20 May 2010 and the drawings attached to Mr Churchill’s email of 1 June 2010 and (ii) the drawings attached to Instruction 85.  The purpose of this comparison was to demonstrate a direct correlation between the parts list and the Instruction 85 drawings.  Mr Aitken accepted that the Instruction 85 drawings contained additional detail in respect of certain elements of the Novum design, and also that there were certain minimal additional items such as stiffeners, but did not consider that there was a completely new design.


Expert evidence
[16]      Mrs Osborne’s opinion on this chapter of the case was based upon a comparison between the T2 and T7 drawings on the one hand and the Novum drawings attached to Instruction 85.  Her view was that the design changed substantially as Novum provided further detail, and that this would have affected the pursuer’s scope of works “for design, fabrication and installation”.  None of the detail was provided in the Sub‑Contract and could not have been anticipated by the pursuer based on the T2 and T7 drawings.  In her opinion, the Novum drawings constituted a variation.  In cross‑examination, she agreed that it could be assumed that the table annexed to Mr Aitken’s email had been used to compile the entry in the Pricing Schedule.  Although the Novum drawings were not an entirely new design, they contained more detail and were more complex than the information in the table.

[17]      Mr Davis’s opinion proceeded upon the basis that at the time of tendering, the pursuer had available to it the T2 and T7 drawings, the table annexed to Mr Aitken’s email, and the drawings attached to Mr Churchill’s email.  On this basis, the drawings attached to Instruction 85 did not represent an entirely new design:  the fundamental features had not changed.  In cross‑examination he agreed that the pursuer could have priced the steelwork on the basis of the T2 drawings and the table alone but would have had to make a lot of assumptions about components such as brackets not shown on those drawings.  The Novum drawings contained increased detail but no change in principle.


Argument for the pursuer
[18]      On behalf of the pursuer it was submitted that the expression “Variation” was a very broad concept as defined in clause 1.3 of this sub‑contract.  If a direction of the defender altered the sub‑contract works in any way, including changing the design in any way, then there was a variation.  Instruction 85 had been admitted by Mr Aitken and Mr Harty to be a variation; on that basis alone the pursuer was entitled to the declarator sought.  The T7 drawings, which were sub‑contract documents, were significantly different from the Novum drawings attached to Instruction 85.  The nature of the connections was not apparent from the parts list in the table.  All that the table did was to tell the pursuer to allow for these quantities in the T7 design, such as it was.  The parties had contracted for the pursuer to build to the T7 drawings with the pricing schedule quantities, however deficient the T7 drawings might have been.  That was the basis against which any variation was to be assessed.  Caution should be exercised in using the pricing schedule to construe the scope of the sub-contract works because, in terms of clause 1.3, its purpose was to provide pricing and payment information and because, in terms of the general preliminaries, items in the pricing schedule were “subject to remeasurement of quantities”.  In any event, the sub‑contract included an “entire agreement” clause which excluded any previous understandings, arrangements and negotiations.  It was not legitimate to draw inferences about what the pursuer had been pricing.  The pricing schedule did not therefore define the entire scope of the ETFE works.  Given the lack of information in the T7 drawings, Instruction 85 amounted to a variation.  In the circumstances, the extent was to vary the sub‑contract obligation from (a) designing and building to the T7 drawings to (b) carrying out the design and other work set out in Variation no 66.


Argument for the defender
[19]      On behalf of the defender it was submitted that the pursuer had failed to prove that there had been any variation of the sub-contract works.  The correct approach was to ask whether the alleged “extra work” was or was not expressly or impliedly included in the work for which the contract sum was payable.  A “change” in the works was not necessarily a variation:  the contract envisaged (clause 13.3.1) the possibility of a direction that increased or reduced expense which was not a variation.  What was priced for by the pursuer in the pricing schedule was the specific and detailed quantities and parts set out in the table rather than anything derived from the T2 drawings.  As the table correlated with the Novum design, there had been no variation.  The true issue between the parties was whether there was sufficient information to price the work: clearly that was the case, and the pursuer had priced its tender under reference to the information in the table.


Decision on Instruction 85
[20]      I agree with the pursuer’s characterisation of variation, as defined in clause 1.3 of the sub‑contract, as a broad concept.  Nevertheless the final words of the definition seem to me to be important:  they make clear that the purpose of the clause is not to render every change in the design, quality or quantity of the sub‑contract works a variation, but rather to restrict the scope of variations to changes in the design, quality or quantity which are required by a direction by the defender.  I do not read the definition as overriding what is described by Keating (Construction Contracts, 9th ed, 2011 at para 37-098) as the “better view” that there is no variation unless the contractor is required to carry out work additional to that necessarily included in the contract. 

[21]      It is therefore necessary to examine whether, on the facts of this case, the work required of the pursuer in terms of Instruction 85 included work additional to that required of it in terms of the sub-contract.  In the light of the evidence of Mr Aitken and Mr Harty that there were some changes relating inter alia to bolts, welding and stiffeners, albeit of a minor nature, which entitled the pursuer to an additional payment, it seems to me that that question must be answered in the affirmative and that the pursuer is entitled to the declarator that it seeks.  This does not, however, address the real dispute between the parties, which is whether there was a very much more extensive variation than the minor items that have been accepted and paid for by the defender. 

[22]      In my opinion there was no such variation.  The works required of the pursuer in terms of the sub‑contract were as set out in the sub‑contract documents: in this context, the T7 drawings and the pricing schedule.  There was no design responsibility.  Supply and fabrication were to be “in accordance with the Engineer’s drawings and specification”.  The only drawings meeting this description were drawings T2 and T7.  I find that both were in the pursuer’s possession at the time of submission of tender Revision D; for present purposes the only difference was that T2 showed all six horizontal rails whereas T7 showed only one.  The important point is that neither of itself contained sufficient detail to enable the pursuer to price the complex arrangement of tubes, brackets and other components making up the secondary support system.  The pursuer was, however, able to submit a price because it had available to it the information contained in the table sent with Mr Aitken’s email.  The appropriate comparison is not, therefore, between the T7 drawings alone and the Instruction 85 drawings, but rather between the works as set out in the T7 drawings, read together with the table, and the Instruction 85 drawings.  It is legitimate, in my opinion, when interpreting the contractual obligation undertaken by the pursuer in terms of the pricing schedule to have regard to the greater degree of specification contained in the table.  Such specification constituted background knowledge available to the parties at the time when the contract was entered into and thus relevant to identification of the intention of the parties (cf Arnold v Britton [2015] AC 1619, Lord Neuberger of Abbotsbury PSC at para 15).  I find the comparison exercise carried out by Mr Aitken to be conclusive in demonstrating a direct correlation between the items in the table and the Novum drawings attached to Instruction 85.  In short, the comparison demonstrates that the work required by Instruction 85 was not (subject to the changes already accepted and paid for by the defender) materially different from the work which the pursuer was obliged to perform in terms of the sub‑contract. 

[23]      I have not placed weight upon receipt by the pursuer of the Novum drawings prior to submission of tender Revision D.  Although I am satisfied that those drawings were in the pursuer’s possession at the time when Revision D was submitted, it is less clear that they were at that time in the hands of the defender which, it will be recalled, had on 20 May 2010 described the table as the best information it had in respect of the ETFE cladding rails.  I do not therefore consider that the Novum drawings can safely be regarded as background knowledge available to both parties at the time when the contract was entered into.

[24]      I also, however, reject the description in the pursuer’s Variation no 66 as an accurate characterisation of the situation that had arisen.  The pursuer had no design responsibility in relation to the secondary support system and could not therefore have had new design requirements imposed upon it.  It may be that more complex drawings were made available to the pursuer with Instruction 85 but these did not reflect any change in Novum’s design.  The comparison carried out by Mr Aitken demonstrates that there was no change in the fabrication or installation requirements in respect of brackets, bracket tubes or embed details.

[25]      In reaching these conclusions I have not derived any significant assistance from either of the expert reports.  Both proceeded upon hypotheses of fact different from that which I have found established in evidence.  Moreover, as was recognised by all concerned, the decision whether an instruction constituted a variation entitling the sub‑contractor to additional payment is one for the court.


[26]      A separate but related dispute in relation to the ETFE cladding arose regarding the tolerances with which the pursuer required to comply in fabricating and installing brackets for attachment of the secondary support structure to the main building frame, and upstands for attachment of the cladding pillow frame to the secondary support structure.  The pursuer seeks declarator that two instructions issued by the defender, namely A2400/501 (“Instruction 501”) and A2400/586 (“Instruction 586”) were variations.  The pursuer’s pleadings in support of such a declarator are sparse.  It is averred that the defender required the pursuer to carry out additional works arising from tolerance issues caused by the new design for the ETFE.  Reference is made to various letters in which it is said that the pursuer set out the tolerance issues.  The pursuer then avers that “in essence the design of the ETFE secondary support system, for which the pursuer was not responsible, failed to take into account the tolerances of the primary steelwork of the main structure and the structural concrete”.  No further specification of the complaint is provided.  Some further explanation was, however, provided in the witness statements of Mr Camacho and Mr Viveiros. 

[27]      At a pre‑proof hearing on 14 April 2016, the defender gave notice that issues regarding the adequacy of the specification of the pursuer’s claim with regard to tolerances were likely to arise at the proof.  It was mentioned in particular that the pursuer’s productions included a report on the appraisal of steelwork tolerances prepared in March 2013 by a firm of consulting engineers with a wealth of detail that did not feature in the pursuer’s case.  At the outset of the proof, counsel for the pursuer sought to refer Mr Camacho to this report.  Objection was taken by the defender on the ground of fair notice.  I sustained the objection.  I have already noted that the pursuer’s pleadings on the tolerance issue are very limited.  It is not, of course, always necessary (or desirable) in commercial cause procedure for the pleadings to set out matters of expert evidence at length.  It will often be preferable for evidence of a technical nature to be brought into proceedings by another method, such as appropriate and targeted reference to material contained in or annexed to an expert report which has itself been lodged and intimated, with due acknowledgment of the overriding principle of fair notice.  The pursuer’s pleaded case here, however, gave no indication of an intention to rely upon any documentation or expert evidence other than the letters it sent to the defender.  The March 2013 report is long and highly technical.  It would not in my opinion have been fair to the defender to allow reference to be made to it, beyond acknowledgment of the fact that it was sent to the defender with the pursuer’s letter dated 12 April 2013 and thus supports the evidence (which was not disputed) on behalf of the pursuer that concerns were being expressed at that time.

[28]      The pursuer’s contractual obligation, in terms of the Structural Steelwork Specification and also Arup’s “Structural Notes”, both of which were sub‑contract documents, was to comply with the National Structural Steelwork Specification for Building Construction (5th edition) (“NSSS”) except in so far as modified by the project specification.  NSSS specifies various tolerances in respect of inter alia accuracy of fabrication and accuracy of erected steelwork. 

[29]      The problem giving rise to the tolerance issue appears to have arisen in September 2012 when Novum were installing the aluminium frame of the cladding to the secondary support system that had by then been manufactured and installed by the pursuer.  Novum alerted the defender to a misalignment of the upstands on the steelwork with the aluminium profiles to the extent that the latter could not be bolted into place.  Mr James McCallum, the defender’s package manager for the steelwork package, took the view that the secondary support system, as fabricated and erected by the pursuer, was outside the contractual tolerances at many locations.  On behalf of the pursuer, Mr Viveiros disagreed.  In his view, the cumulative effect of tolerances in the steel work and concrete of the main building frame and in the aluminium profile of the cladding was to require the pursuer to work to a tolerance of +/- 0mm, which was impossible to achieve.  This was how he put the problem in a letter dated 9 October 2012 to the defender’s project manager, Richard McInally.  At a meeting on 10 October 2012 attended by Mr Viveiros and Mr McCallum among others, the pursuer was “reminded” (according to the defender’s note of the meeting) that Novum could work to a tolerance of +/- 10mm.  The pursuer’s representatives asserted that the pursuer was entitled to work to +/- 20mm.  The defender disagreed and on 12 October 2012 Mr McInally wrote to Mr Viveiros referring to the relevant provisions of NSSS. 

[30]      On 19 October 2012, the defender issued Instruction 501 to the pursuer in the following terms:

“The results of the survey of the ETFE steelwork to sector 1.2 (issued to Martifer via LL email of 11.10.12) show that this steelwork, as erected does not meet the accuracies required by the specifications included in your subcontract.  You are instructed to carry out the  alterations that are necessary to meet you obligations with respect to these specifications.  Once altered the steelwork should be accurate to a tolerance better than +/- 10mm.  You are required to forthwith comply with this instruction…”


[31]      The position of the pursuer’s witnesses, Mr Camacho and Mr Viveiros, was that the pursuer, as fabricator and erector of the secondary support system, was contractually entitled to work to a tolerance of +/- 20mm.  No specific contract document was referred to in support of that position.  As I understand it, it reflects what these witnesses considered to be the minimum tolerance that was practically achievable when one had regard to tolerances allowed in the main building frame and in Novum’s aluminium profile.  Reference was also made in the submissions on behalf of the pursuer to an Arup report dated February 2010 entitled “Movement and Tolerances Report”, incorporating in turn a section from the 4th edition of NSSS, showing permitted deviations for steel columns from plumb of up to +/- 25mm over full building height.  On this basis, it was asserted that the instruction to work to tolerances better than +/- 10mm constituted a change imposing a more onerous obligation.  On behalf of the defender, Mr McCallum’s position was very different.  According to his evidence, the wishbone brackets which formed part of the secondary support system steelwork and attached it to the main building frame had design features, including slotted holes, which permitted deviations from tolerance in the main frame (in whatever direction) to be eliminated, bringing the secondary system into the “correct” position vis à vis the cladding frame.  In his view, the instruction to achieve a tolerance better than +/- 10mm represented a relaxation of the pursuer’s contractual obligation as some of the tolerances in NSSS were lower.  The problem, according to Mr McCallum, was that the upstands were out of position.

[32]      In my opinion this branch of the pursuer’s claim cannot succeed because it has failed to establish that it was permitted in terms of the sub‑contract to work to a tolerance greater than the tolerance of +/- 10mm specified in Instruction 501.  No sub‑contract document referring to a tolerance of +/- 20mm was brought to my attention.  I do not consider that the excerpt from NSSS incorporated into the Arup Movement and Tolerances Report provides any support for the pursuer’s contention.  As Mr McCallum pointed out, the figure of +/- 25mm refers to deviation from plumb of the top of a steel column and is quite different from a tolerance applying to the location of brackets and holes in brackets throughout the secondary support system.  The contractual tolerances were those set out in NSSS.  The figures vary depending upon the nature of the component, but they include tolerances significantly lower than +/- 10mm for features such as fittings and attachments on primary members.  I am inclined to agree with Mr McCallum’s view that to some extent the requirement of a tolerance better than +/- 10mm (which was sufficient for Novum’s purposes) represented a relaxation of the pursuer’s contractual obligation, but for present purposes it is sufficient for me to hold that the pursuer has failed to prove that Instruction 501 imposed an obligation more onerous than that which it had undertaken in terms of the sub-contract.  It is not therefore entitled to the declarator sought with regard to Instruction 501.


Instruction 586
[33]      The position is different as regards Instruction 586.  This instruction concerned tolerance difficulties that arose in relation to attachment of the secondary support system to concrete (as opposed to steel) columns in the main building frame.  This matter was dealt with in Mr Harty’s witness statement and was not subject to cross-examination.  According to Mr Harty’s evidence, the problem addressed by Instruction 586 arose because the concrete sub‑contractor had incorrectly positioned cast-in brackets in the concrete columns, with the consequence that bracket plates to which wishbone brackets were to be attached could not be connected to the concrete column.  On 2 April 2013, the defender issued Instruction 586 to the pursuer with the subject heading “ETFE and Out of Tolerance Walls at GL14-15” stating as follows:

“Martifer are instructed to undertake a feasibility study regarding possible alterations to the ETFE structural steel in the location of GL14-15 at L4 and L5 due to concrete tolerance issues.”


It is accepted by the defender that this instruction was a variation.  The defender’s position is that the pursuer has been paid for it, in pursuance of Variation no 466, submitted to the defender on 29 May 2013.  The sum claimed was £14,300.64;  Mr Harty assessed the amount due at £10,462.34, which was paid.

[34]      As there is no dispute between the parties that Instruction 586 was a variation, I consider that the pursuer is entitled to declarator to that effect.  Whether such declarator is of any practical significance remains to be seen.  The question whether the pursuer has been paid for the variation will be a matter for proof, although I observe that at present the pursuer has no pleadings admitting or denying that it has been paid in respect of Instruction 586; nor was the matter addressed in its evidence.  I shall hear parties as to what further procedure, if any, is necessary with regard to this branch of the claim.


Load changes
[35]      The engineer’s drawings provided by Arup to the pursuer included drawings setting out loading information for the steel to steel connections in the structural steelwork.  These drawings were sub-contract documents.  In the course of construction, design changes resulted in alterations to the required load‑bearing capacities of a large number of connections.  The pursuer identified 42 different types of connections whose load‑bearing capacities were changed.  The defender accepted that 41 of these changes constituted variations.  The issue between the parties is confined to one type of connection, referred to as Type V connections.  These connections are located at a crank in the lower end of ten raking beams where they become horizontal before bearing on a concrete wall.  Loadings for the beams were provided at tender and construction stages in drawings by Arup.  On the basis of the information provided by Arup the pursuer intended at tender stage to fabricate the beams with partial penetration butt welds from each side at the crank.  It is common ground between the parties (i) that Arup produced revised loadings during the construction stage, necessitating an increase in the size of the weld, and (ii) that the pursuer fabricated each Type V connection with a full penetration weld.  It is also agreed between the parties’ respective expert witnesses (contrary to the pursuer’s pleaded case) that although the loads on the crank were varied between tender and construction, the variation was not to the extent that a fully welded connection was required.

[36]      The pursuer seeks declarator in this action that each of a lengthy list of specified instructions by the defender was a variation.  These instructions all relate to changes of connections necessitated by increases in loadings during the construction stage.  I understand the defender’s position to be that this branch of the pursuer’s claim is appropriate for proof on quantum except in so far as it relates to Type V connections, in respect of which the defender is entitled to absolvitor.

[37]      It was not asserted by the pursuer’s witnesses that the change to a full penetration weld for Type V connections had been the subject of a written instruction.  It was contended rather that the evidence demonstrated that the defender had, through its consulting engineer Woolgar Hunter, directed the pursuer that Arup would have required a full penetration weld.  Reference was made to a file note dated 17 April 2012 by a representative of Woolgar Hunter of a site meeting on the previous day attended by representatives of the pursuer and the defender.  The file note contains a number of “key points” including the following:

“The connection Type V is considered to be fabrication (beam crank) rather than a ‘connection’.  The connection loads quoted by Martifer are considered to refer to the steel to concrete connection, which is adjacent to the beam crank.  Although Martifer provide a calculation to show that partial penetration butt welds would be sufficient (based on tender loads), it is not considered that this would have been accepted by Arup.  It is considered that a competent contractor should have allowed a full penetration butt weld at the beam crank.  Martifer to provide evidence of use of partial penetration butt welds at beam cranks on other projects.”


However, Mr McCallum’s evidence, which I did not understand to be disputed, was that by the time of this meeting the steelwork had already been constructed.

[38]      Mr Camacho also incorporated in his witness statement an excerpt from a report by Woolgar Hunter dated 3 April 2012, which compared the Type V connection solution in the tender and as constructed.  The report includes the following comments on connection suitability:



  • Fabrication of crank beam involves welding two sections of beam;


  • All welding will be done in shop;


  • Martifer calculations show minimum 2.6mm flange welds required(9mm proposed) and minimum 2.41mm web welds required (8mm proposed);


  • Proposed welds are approximately 300% longer than required.




  • Connection detail has not changed in principle; welds have changed from partial penetration to full penetration;


  • No calculations have been provided for the revised construction design;


  • On basis of tender design calculations it is considered that the original connection design may theoretically have worked or that only a minimal increase in weld size would be required.”


Apart from anything else, this report appears to confirm that by April 2012 construction of the steelwork containing the Type V connections had taken place.

[39]      Neither of these documents therefore answers the question why the pursuer carried out full penetration welds in the Type V connections.  In his oral evidence, Mr Camacho stated that the pursuer had been told by the defender at meetings to do full penetration welds because this was what Arup would have required.  He was unable to state whether this had taken the form of a written instruction.  No calculation of the size of weld had been carried out because the defender’s position had been that, independently of the load, a crank beam required a full penetration weld.  No calculation was needed where a full penetration weld was used.  I found Mr Camacho’s evidence on this branch of the case unsatisfactory.  His assertions that the pursuer had been obliged to carry out full penetration welds appeared to be based on the Woolgar Hunter file note of a meeting which, as I have already observed, came too late to be capable of being the occasion of an instruction to change the weld.

[40]      At the close of the proof, it was submitted on behalf of the pursuer that the instruction to change to full penetration welds had been a verbal instruction given to the pursuer at a site meeting on an unspecified occasion by Woolgar Hunter, on behalf of the defender.  I am not satisfied that it has been proved that any such instruction was given.  I regard it as inherently unlikely that a matter such as this would have been addressed so casually.  In any event it cannot have been given on the occasion upon which Mr Camacho stated that it was given, namely the site meeting on 16 April 2012.  No other evidence vouching the giving of a verbal instruction was produced.  I therefore hold that the pursuer has failed to prove that the variations admittedly agreed by the defender in respect of additional loadings included the Type V connections.


Roof curvature
[41]      The roof of the Hydro is a complex structure.  I have already noted that it takes the form of a dome set at an angle to the ground, and that it is circular in the plane of the ring beam that runs around the circumference of the dome.  It is a proprietary roofing system manufactured by Kalzip Limited, a member of the Tata Steel Group, comprising a series of layers, described in the architect’s specification (work section H31 at H31.2103) as follows:

“A metal sheet roof cladding system consisting of an outer standing seam sheet with thermal and acoustic insulation layers, acoustic boards, acoustic membranes and internal perforated liner sheet fixed to a secondary support structure…”


For present purposes I am concerned primarily with the outer layer of the roof.  It consists of six concentric spans of tapered standing seam aluminium sheets attached by clips known as halter clips to steel sections known as top hats (because of their shape), which are in turn fixed to a perforated galvanised steel roof deck.  The aluminium sheets are manufactured flat, not curved, but have a degree of flexibility:  they may for example flex when walked upon, depending upon how far one is from the nearest clips.  The acoustic and vapour control layers are located, together with a layer of insulating material, over the roof deck but beneath the top hat sections.

[42]      It is, I hope, uncontroversial to begin by stating that the exterior of the roof as constructed has the appearance of being curved.  The issue between the parties is whether achievement of the degree of curvature in the roof as constructed constituted a variation of the pursuer’s obligations under the sub‑contract.  The pursuer submits that its contractual obligation was to construct a facetted roof, and that a direction by the defender to reduce the visual effect of facetting was a variation.  The defender submits that the pursuer’s contractual obligation was to construct a curved roof and that since the roof as constructed accords with that obligation, there has been no variation.


Relevant sub-contract documents
[43]      In support of their respective contentions, the parties sought to derive support from various sub‑contract documents and drawings.  I note here that clause 2.2 of the sub‑contract provides that if any conflict appears between the sub-contract drawings (ie drawings included in the sub‑contract documents) and the remainder of the sub‑contract documents, the latter shall prevail.

[44]      I have already quoted the relevant provision of the architect’s specification.  Two further points may be mentioned with regard to the specification.  Firstly, at paragraph H31.2200(b)(i), under the heading “Materials”, the specification provides that “the metal roofing shall consist of pre‑manufactured (walkable) standing seam sheets laid to profile of roof”.  Secondly, in the specifications register, work section H31 is categorised as “Descriptive”, which means that:

“The section, when read with the Design Drawings, indicates the visual intent with which the Contractor must comply when undertaking the Detailed Design”.


[45]      The next sub‑contract document of relevance is the pricing schedule for work section H31.  Under a sub-heading “Metal profiled/flat sheet cladding/covering/siding”, the pricing schedule provides for “CONTRACTOR DESIGNED: Roof cladding system: Metal sheet roof cladding system consisting of an outer standing seam sheet with thermal and acoustic insulation layers, acoustic boards, acoustic membranes and internal perforated liner sheet, fixed to a secondary support structure; as specification clause H31.2103 and all other relevant specification sections”.  Each layer of the roof is then further described.  The external sheet is described as follows:

“Proprietary tapered aluminium allow standing seam sheets in single lengths, end laps shall not be permitted; thickness 0.9mm as recommended by the manufacturer; Natural stucco embossed finish as agreed and accepted by the [project manager] via samples; welded joints as recommended; curved and circular; as 3D model”.


(Emphasis added.)  The words “curved and circular” also appear in the descriptions of all of the other layers making up the roof cladding/covering.

[46]      Extensive reference was made during the proof to an architect’s drawing numbered A-1274, dated 11 January 2010 and entitled “Geometry method statement ‑ roof outer defining surface”.  This sub‑contract drawing includes a section across the dome entitled “Generative roof surface section” which the pursuer founded upon as demonstrating that the outer surface of the roof was intended by the architect to be facetted. 

[47]      After submission of the pursuer’s tender but before execution of the sub‑contract agreement, the defender issued an instruction (number A2400/1) comprising a large number of drawings and other documents.  One of these was a revised version of the engineer’s

General Structural Specification (SR101), Construction Issue C1.  This version included an expanded specification in respect of roof purlins, the design and detailing of which was to be the responsibility of the roofing sub-contractor.  The revised specification contained the following requirement:

“The roof cladding/purlin design to be detailed to create the curved roof geometry between the outer surface defined on the Architect’s drawings and the facetted roof geometry of the top chord of the roof steelwork.”


Construction of the roof cladding
[48]      At about the time of commencement of works on site in 2011, and prior to the carrying out of any roofing works, the pursuer submitted proposals to the defender for certain amendments to the design of the roof cladding support.  One feature of those proposals was that the roof purlins would be omitted.  The architect raised a concern that this would result in a visible “kink” in the curvature of the roof at the level of the lowest span of roof sheets.  Pending resolution of this issue, the pursuer’s proposal was not approved.  Having consulted Kalzip representatives, the pursuer’s project manager Mr Marcelo Santos emailed the defender’s Mr Kenneth Stewart to advise him that Kalzip had suggested a “clever solution”, namely to use variable heights of halter clips on the last span to accommodate differences in height of the top of the steelwork.  A drawing produced by the pursuer in connection with this proposal shows use of clips of four different heights, together with spacers allowing further differing heights to be achieved.  This solution was acceptable to the architect and to the defender, and construction of the roof proceeded with purlins omitted.

[49]      Construction of the roofing system began in early 2013.  When the pursuer came to install the halter clips to which the external sheets would in due course be attached, clips of a uniform height were used throughout the roof, with the exception of the last span as previously agreed.  On 7 February 2013, the architect’s Mr David Gillespie visited the site and on the following day he expressed concern in an email to Mr McCallum that no clear methodology had been provided by the pursuer for “achieving the design geometry of the roof”, and stated his expectation that a thorough method statement would be provided, complete with diagrams and calculated positions for the clip positions, “to ensure that the [architect’s] GMS roof curvature is met”.

[50]      In terms of paragraph A.4009 of the architect’s specification, the pursuer was obliged to offer complete sections of certain elements of its works as a quality benchmark for acceptance by the employer’s project manager.  In accordance with paragraph H31.1306 of the specification, this requirement applied to the roof cladding.  The pursuer assembled two segments of Kalzip external sheeting for the purpose of obtaining benchmarking approval.  A benchmarking inspection took place on 6 March 2013.  The segments constructed were judged by the employer’s project manager to be unacceptable for the following reasons, set out in a letter sent to the defender on the following day:

“1.  The Kalzip is installed facetted which does not achieve curved roof geometry required either by the Architect’s design intent and/or as required under the Contract Drawings and Specifications.  Also that in addition to the visible facets there are visible bows and dips/hollows.


2.  The Halter Clips as installed are neither packed to achieve curvature nor it would appear have varying height Halter Clips been utilised.”


The roof was regarded as having “failed to achieve the fundamental requirement of being curved”.  The project manager also noted, however, that the pursuer’s representative at the meeting had informed him that it had always been the pursuer’s intention to install a facetted roof, and not a curved one.  He regarded this as an unauthorised fundamental departure from the roof design that the defender was required to provide and expressed the opinion that the pursuer required immediate instruction from the defender to comply with the contract.  On 10 March 2013, the defender’s project manager, Mr Richard McInally, emailed Mr Camacho in the following terms:  “If you are not going to acknowledge agreements made that improve the profile you must stop laying immediately”.

[51]      The pursuer’s response to these criticisms was most clearly expressed in an email dated 12 March 2013 from Mr Viveiros to Mr McCallum.  Mr Viveiros noted:

“1.  The roof is technical well-built and following every Kalzip specification, and has been reviewed regularly by Kalzip.


2. On a roof that is not built with curved steel, and that has only faceted materials (deck, acoustic board and Kalzip tapered sheet), it is not possible to obtain a final result with a curve shape.  We are building it to a curve formed by faceted segments.”


Mr Viveiros noted that from the ground the roof appeared curved, in accordance with design intent, and asserted that this was what had always been the contractual solution approved by the architect and by the defender.  In his view, the works were being done in accordance with the specification.

[52]      A further meeting was held on 19 March 2013.  The minute states “Martifer will complete their survey of the roof in order to offer-up a sample of ‘perfectly curved roof’”.  On 23 March, Mr Viveiros produced a method statement entitled “Assembly of curved roof ‑ alternative assembling method”.  The critical feature of this method statement was the use of halter clips of varying heights, together with spacers where necessary, at carefully calculated locations across the roof.  Construction of the roof proceeded according to this method statement and subsequent revisions, and assembly of the Kalzip sheets was completed in May 2013.  On 18 April 2013, the pursuer submitted Variation no. VR 470 “for the costs associated with the revised roof installation”.  By letter dated 3 July 2013, the defender declined to make any payment in respect of a variation. 

[53]      The visual difference between a facetted roof and a curved roof is apparent from photographs lodged in process and referred to at the hearing.  Photographs taken from gutter level at about the time of the benchmarking exercise clearly show bends in the standing seams of the Kalzip sheets caused by the need to fit the sheets to clips whose height was dictated by the underlying facetted steelwork.  Another photograph (production 7 in the joint bundle) taken from a distance at about the same time shows a segment of constructed Kalzip sheet which, although giving a general impression of being curved, can still be perceived on closer inspection to be facetted where sheets have been bent to permit attachment to the steelwork profile.  In contrast, photographs of the roof as built show a remarkably regularly curved dome with no apparent kinks or bends. 


Evidence of expert witnesses
[54]      Mrs Osborne found the architect’s drawings confusing and ambiguous, but did not find any clear indication in them that the roof was to be constructed with a smooth curve.  Her opinion was that a smooth curve was unusual, expensive and difficult to achieve, and that if that was what the architect had wanted, he would have had to make it clear in the drawings.  In the absence of such clear indication, a facetted roof giving the appearance of a curve was what the contract required.  The reference in the architect’s specification to the sheets being “laid to profile of roof”, where the roof steelwork was facetted, showed that a facetted external layer was required.  Properly interpreted, architect’s drawing A-1274 also showed the roof outer surface as facetted.

[55]      Mr Davis considered that the sub-contract required the Kalzip sheets to follow a true curved profile.  This was based partly upon his interpretation of the sub‑contract documents and drawings, and partly upon Kalzip’s technical requirements.  Those requirements included the need for the sheets, once assembled, to slide freely across the halter clips in order to enable thermal expansion and contraction.  Such movement could not occur if there were kinks in the profile of the sheets which would cause the standing seams to bind against the clips and become locked.  Drawing A-1274 provided information about the setting out of the steelwork;  it would not be reasonable to impose the geometry intended for the roof steelwork on to the roof cladding.  The Kalzip roof sheets installed by the pursuer at the time of the benchmarking exercise did not meet the sub-contract requirements because they did not achieve a curved profile.


[56]      The question whether the defender’s direction to the pursuer not to proceed with the roof cladding work until a curved profile could be achieved constituted a variation is one for the court and not for the opinion of the expert witnesses.  It must be answered by comparing the pursuer’s contractual obligation with what was required by virtue of the defender’s direction.  I start, however, with some further observations about the Kalzip sheeting.  On the basis of the evidence led before me, it is clear that any facetting in the outer layer of the roof as constructed would result not from the fact that the sheets were manufactured flat (creating facets at joints between concentric rings of sheets) but rather from the fact that they were being laid on a framework of steel which was inevitably facetted (creating bends ‑ or facets ‑ at the underlying steel members).  It is also clear that it is feasible to take measures to reduce the magnitude of such facetting and thereby reduce, or even eliminate, its visual impact.  That was indeed the effect of the solution employed by the pursuer on two separate occasions:  the first when the roof purlins were omitted from the design and concern was expressed regarding a kink at the lowest span of roof sheets, and the second in response to the failed benchmarking exercise.  On both occasions the visual impact was eliminated by the use of halter clips of varying heights, with or without spacers.  But were such measures required of the pursuer in terms of the sub-contract?

[57]      In my opinion the excerpts from the sub-contract documents relied upon by the pursuer do not support the contention that its obligation was to construct a facetted roof.  The first passage founded upon was the reference in the architect’s specification to the sheets being “laid to profile of roof”.  These words appear in the specification of materials to be used in construction of the roof cladding and not in a description of the design.  In my view the pursuer’s contention seeks to read too much into them; they appear to me to be essentially neutral, leaving open the question, to be answered elsewhere, of what the profile of the roof was to be.  It is not legitimate to read “profile of roof” as synonymous with “profile of underlying steelwork”.  In any event, it is significant to note that this specification pre‑dates the design change promoted by the pursuer in terms of which the purlins, which may have contributed in the original design to achievement of a curve, were omitted. 

[58]      I turn then to architect’s drawing A-1274.  Mr Davis’s interpretation of this drawing was that the “outer roof surface”, shown as consisting of a facetted roof arc with 12 equal chords between the edge of the roof and the oculus, depicted the members of the top chord of steelwork.  The reason for this was that the arc on the drawing ran through the ring beam cut line.  It could be seen from other drawings (which are not sub‑contract drawings) that the ring beam was at the level of the roof top chord and below the level of the roof cladding.  I accept this opinion.  The reference to “chords” in the “generative roof surface section” 01 seems to me of itself to confirm that what is depicted is steelwork; the word has no sensible meaning when applied to the outer layer of cladding.  For the reasons given earlier in this opinion, I regard it as legitimate to have regard, as background knowledge common to both parties at the time of entering into the sub-contract, to other evidence of the relationship between the various roof layers and the ring beam in order to confirm which layer is shown as intersected by the plane of the roof beam in drawing A-1274.  From drawing A-1326, dated 2 November 2010 and entitled “Geometry method statement: roof build-up zones”, it is more readily apparent that the ring beam is located at the level of the bottom of the purlin zone, ie at the level of the top steel chord and below the level of the outer cladding.  There is no evidence of a change of design in this respect. 

[59]      I found Mrs Osborne’s evidence regarding drawing A-1274 unpersuasive.  She maintained that the line on section 01 was only a section line, but it is clearly labelled as being the ring beam cut line.  She made the valid point that there were risks in reading drawings together that were prepared at different times for different purposes, but did not offer any reason why drawing A-1326 could not be referred to in order to confirm the position of the ring beam in relation to the roof layers.  I did not share her view that drawing A-1274 was so confusing that no conclusion could be drawn from it.

[60]      I find, therefore, that there was nothing in the sub-contract documents which specified, or could reasonably be interpreted as specifying, that the pursuer’s contractual obligation was to construct a facetted roof.  On the other hand, the pricing schedule explicitly describes the outer layer of the roof as “curved and circular”.  I see no reason to read this as imposing a lesser requirement than the words themselves indicate.  Contrary to the apparent understanding of the pursuer’s witnesses, the roof is circular: it is not elliptical albeit that it appears so in plan because it is set at an angle to the ground.  Nor, as the completed work demonstrates, was it impossible to achieve a curvature without visible facets.  Moreover,  Issue C1 of the General Structural Specification, another document within the common knowledge of the parties at the time of conclusion of the sub‑contract (and, indeed, within such knowledge at a time when it was not yet known which documents would be sub‑contract documents ) contained the requirement that the roof cladding/purlin design be detailed “to create the curved roof geometry between the outer surface defined on the Architect’s drawings and the facetted roof geometry of the top chord of the roof steelwork”.  Although I have found the syntax of this requirement somewhat obscure, I am satisfied, having heard the expert evidence, that the intention was to make clear that the roof design had to accommodate the fact that the roof steelwork was facetted while achieving an outer surface that was curved.  I reject Mrs Osborne’s opinion that if the architect had wished to specify a curved roof he would have used the expression “smooth curve”; this particular roof had a very large surface area and design responsibility for achieving the requisite curvature was placed clearly upon the pursuer.

[61]      I accept Mr Davis’s evidence that functional problems would arise if the Kalzip sheets were laid in such a way as to render it impossible for them to slide over the halter clips when undergoing contraction or expansion, and that it was a feature of the Kalzip roofing system that intentional or inadvertent fixed points within the roof structure had to be avoided.  However, in the absence of clear evidence that this feature of the system was in the minds of the parties at the time when the sub‑contract was entered into, I have not attached significant weight to it.  I have also disregarded references by Mr Davis in his evidence to a 3D model which was not produced in evidence at the proof.

[62]      In summary, I hold that the terms of the sub-contract imposed an obligation upon the pursuer to design and construct a curved as well as a circular roof.  No doubt this was more difficult ‑ and more expensive ‑ to achieve than a facetted roof which had the appearance of being curved when viewed from a distance or from ground level, but that, in my opinion, was the obligation undertaken.  It follows that the defender’s direction to the pursuer to alter the design of the roof to reduce the facetting present at the time of the benchmarking exercise was not a variation, and the pursuer is not entitled to declarator to that effect.


[63]      The interlocutor to be pronounced giving effect to my judgment will not be a straightforward one.  Before pronouncing any order, I shall hear parties’ submissions in relation to its terms, and also as to what further procedure is required in this action.