Delay Claims in Spanish Construction Arbitration

Delay claims are among the most technically demanding disputes in Spanish construction arbitration. They usually arise when the contractual completion date is exceeded and one party seeks either additional time, compensation for prolongation costs, or delay damages, while the other party seeks liquidated damages/penalties for late completion.

Spanish law does not treat every delay as automatically compensable. The central questions are usually:

1. What caused the delay?
2. Who was responsible for it?
3. Was the delay critical to completion?
4. Was an extension of time available under the contract?
5. Was the claim notified and documented in accordance with the contract?
6. What actual loss resulted from the delay?
7. Does the contractual penalty apply, and can it be moderated?
8. How should concurrent or overlapping delays be treated?

The Spanish Supreme Court's construction jurisprudence is particularly important to arbitral tribunals because it supplies persuasive principles concerning contractual interpretation, attribution of delay, penalties, proof of damages and quantification of prolongation costs. For public works, the jurisprudence concerning the Spanish public-contracting regime is especially significant.

1. Legal framework

A. Spanish Civil Code

For private construction contracts, the principal provisions include:

• Article 1091 — contractual obligations have the force of law between the parties.
• Articles 1101 and 1106 — contractual liability and compensation for damages.
• Article 1100 — default/mora.
• Article 1124 — resolution for reciprocal contractual breach.
• Article 1152 — contractual penalty clauses.
• Article 1154 — judicial moderation of penalties in circumstances contemplated by the provision.
• Articles 1281–1289 — contractual interpretation.

These provisions interact closely with the actual construction contract. In arbitration, the tribunal normally begins with the parties' agreed allocation of delay risk.

2. Public construction contracts

Where the project is a Spanish public works contract, the analysis is substantially influenced by the Ley 9/2017, de Contratos del Sector Público (LCSP).

Important principles include:

• the contractor generally operates under the risk and ventura principle;
• delay attributable to the contractor can produce penalties;
• delay attributable to the contracting authority or circumstances legally qualifying for compensation may entitle the contractor to compensation;
• extensions of time can be available in circumstances recognised by the contractual and statutory regime;
• the contractor must establish the causal connection between the event and the additional costs.

The Supreme Court has made clear that an increase in the execution period caused by circumstances attributable to the Administration does not necessarily fall within the contractor's ordinary commercial risk.

3. What constitutes a delay claim?

A delay claim may take several forms.

Contractor's claim

The contractor may claim:

• extension of time;
• prolongation costs;
• additional site-management expenses;
• extended equipment costs;
• additional personnel costs;
• extended insurance and guarantees;
• additional financing costs;
• increased overheads;
• loss of productivity;
• disruption;
• loss of profit, where legally and contractually recoverable;
• price escalation caused by prolonged execution.

Employer's claim

The employer may seek:

• contractual delay penalties;
• damages for late availability of the facility;
• additional financing costs;
• lost revenue;
• costs of alternative accommodation or facilities;
• consequential losses where recoverable;
• termination/resolution in sufficiently serious cases.

4. The fundamental issue: attribution of delay

The most important question is generally whether the delay is attributable to the contractor.

A contractor will have a substantially stronger claim where the delay resulted from:

• late possession of the site;
• late design information;
• employer variations;
• defective employer-supplied designs;
• late approvals;
• delayed instructions;
• interference by the employer;
• unforeseen site conditions attributable to the employer;
• governmental acts;
• delayed permits for which the employer assumed responsibility;
• suspension ordered by the employer.

Conversely, the employer has a stronger case where the delay resulted from:

• inadequate mobilisation;
• insufficient labour;
• poor project management;
• defective workmanship;
• late procurement;
• contractor design failures;
• subcontractor failures;
• inadequate equipment;
• financing problems of the contractor.

Spanish Supreme Court jurisprudence repeatedly emphasises the need to determine imputability, rather than simply establishing that the contractual completion date was exceeded.

5. Critical delay

Not every delay affecting an activity necessarily delays the contractual completion date.

A useful distinction is:

Activity delay → project delay → critical-path delay → compensable delay

For example:

A subcontractor is 20 days late in installing internal doors.

If the doors were not on the critical path and other work could proceed, the project may not have suffered 20 days of compensable delay.

But:

The employer delays approval of the structural design by 90 days, preventing the foundation works from commencing.

If the foundation lies on the critical path, the resulting delay may extend the contractual completion date.

An arbitral tribunal therefore normally examines:

• baseline programme;
• updated programmes;
• critical path;
• actual progress;
• contemporaneous correspondence;
• programme revisions;
• site diaries;
• engineer's reports;
• payment certificates;
• variation orders;
• extension-of-time records.

6. Concurrent delay

Concurrent delay is particularly contentious.

Suppose:

• Employer-caused delay = 60 days;
• Contractor-caused delay = 40 days;
• Both overlap for 30 days.

The tribunal must determine whether the contract or applicable law permits recovery for the overlapping period.

The analysis should not simply add all delay events. The tribunal should identify:

1. the start date of each delay;
2. its duration;
3. its effect on critical activities;
4. whether another event was simultaneously delaying completion;
5. whether either event independently would have caused the same completion date.

A properly prepared critical-path analysis is therefore often more important than merely counting days.

7. Extension of time

An extension-of-time claim is conceptually different from a monetary claim.

An extension answers:

When should the contractor have been required to finish?

A damages claim asks:

What financial loss resulted from the delay?

The two claims are nevertheless closely connected.

For example:

Original completion: 30 June
Employer delay: 90 days
Revised completion: 28 September

If the tribunal accepts the 90-day extension, a delay penalty calculated against the original completion date may become inappropriate for those 90 days.

Conversely, if the contractor fails to establish entitlement to the extension, the employer may argue that delay penalties continue to accrue.

8. Delay penalties and cláusula penal

Spanish construction contracts frequently contain clauses providing for a fixed amount for each day or week of delay.

A typical structure is:

€X per day of delay, subject to a maximum percentage of the contract price.

The important issues are:

• whether the clause is actually applicable;
• the contractual completion date;
• whether extensions were granted;
• whether the delay was attributable to the contractor;
• whether employer-caused delay displaced the penalty;
• whether the contractual cap applies;
• whether Article 1154 CC permits moderation in the circumstances.

9. Case Law 1 — STS 556/2017, 16 October 2017

Contract of works — delay penalty and imputability

Tribunal Supremo, Sala Primera, Sentencia 556/2017, 16 October 2017, ECLI:ES:TS:2017:3720

This is one of the most directly relevant Spanish Supreme Court decisions concerning construction delay penalties.

The dispute concerned a construction contract and a penalty for delay. The Supreme Court focused on the need to establish whether the delay was imputable to the contractor rather than mechanically applying the contractual penalty merely because completion occurred after the contractual date.

Importance for arbitration

The case illustrates a fundamental proposition:

A delay penalty must be examined together with the cause and attribution of the delay.

An arbitral tribunal should therefore construct a chronology rather than simply compare:

contractual completion date vs actual completion date.

The tribunal should ask:

• Which party caused each period of delay?
• Did employer variations affect completion?
• Did the employer interfere with the works?
• Were there excusable events?
• Was the contractor itself already in delay?

This is particularly important where the employer seeks substantial liquidated damages.

10. Case Law 2 — STS 28/2016, 4 February 2016

Contractor delay and moderation of contractual penalty

Tribunal Supremo, Sala Primera, Sentencia 28/2016, 4 February 2016, ECLI:ES:TS:2016:356

This case involved a construction contract, delay attributable to the contractor and a contractual penalty. The Supreme Court addressed the doctrine surrounding moderation of the penalty under Article 1154 of the Civil Code.

Arbitration significance

The case is important because Spanish tribunals distinguish between:

• determining whether a penalty clause applies; and
• determining whether the circumstances justify judicial moderation.

An arbitral tribunal should therefore not assume that every agreed penalty is automatically reduced simply because it appears substantial.

The contractual mechanism and the circumstances surrounding the breach must be analysed.

11. Case Law 3 — STS 330/2020, 22 June 2020

Contractual completion date and delay penalties

Tribunal Supremo, Sala Primera, Sentencia 330/2020, 22 June 2020, ECLI:ES:TS:2020:1995

This case concerned a construction contract involving penalties for delay, the date on which completion should be assessed and the interpretation of contractual provisions concerning the completion deadline.

Key lesson

The contractual wording concerning the completion date is crucial.

The tribunal must identify:

• the agreed completion milestone;
• what constituted "completion";
• whether practical completion or formal acceptance was required;
• whether contractual modifications changed the date;
• whether the evidence supported the alleged completion date.

This is particularly important in arbitration because construction contracts frequently contain different dates for:

• substantial completion;
• mechanical completion;
• testing;
• provisional acceptance;
• final acceptance.

A party should not automatically equate the final administrative acceptance date with the date on which contractual delay ceased.

12. Case Law 4 — STS 202/2016, 1 April 2016

Abandonment of works and quantification of delay damages

Tribunal Supremo, Sala Primera, Sentencia 202/2016, 1 April 2016

The Supreme Court considered delay resulting from the unjustified abandonment of construction works. It assessed a defined period of abandonment and accepted a damages calculation based upon expert evidence concerning the larger delay-related losses. The reported calculation included both damnum emergens and lucrum cessans.

Importance

This case demonstrates that delay damages require a sufficiently reliable causal and evidentiary foundation.

The Court did not simply award an arbitrary amount for "delay."

Instead, it considered:

• duration of the actionable delay;
• expert evidence;
• actual economic consequences;
• the claimant's own contractual conduct.

Arbitration lesson

A claimant should therefore prepare a damages model such as:

Delay period × proven monthly cost = prolongation claim

rather than simply submitting a global percentage without explanation.

13. Case Law 5 — STS 1423/2022, 2 November 2022

Administrative construction delay and indirect costs

Tribunal Supremo, Sala Tercera, Sentencia 1423/2022, 2 November 2022, ECLI:ES:TS:2022:4068

This is one of the most important cases for delay-cost quantification in Spanish construction disputes.

The case concerned additional costs arising from delays attributable to the public administration. The Supreme Court held, in substance, that increases in the execution period caused by circumstances attributable to the Administration are not, as a general rule, simply part of the contractor's risk and ventura.

The Court also accepted that indirect costs can, where properly justified, be calculated through an estimated percentage of relevant general costs.

Particularly important point

The Court rejected an insufficiently reasoned percentage calculation.

The percentage must be:

• justified;
• reasonable;
• connected to the characteristics of the project;
• supported by evidence.

The decision ultimately recognised substantial delay-related costs in the underlying infrastructure dispute.

Arbitration significance

This case is extremely useful where a contractor claims:

• extended site overhead;
• site office costs;
• project management;
• temporary facilities;
• supervision;
• security;
• equipment;
• administrative personnel.

It supports the proposition that indirect costs may be recoverable even where exact individual invoices cannot capture every element, provided the methodology is sufficiently justified.

14. Case Law 6 — STS, 2 April 2008

Prolongation and indirect/general costs

The Supreme Court considered additional costs resulting from an extended period of execution and recognised that where delay is established, the contractor may have to maintain the material and human resources associated with the project, thereby generating additional indirect costs.

The Court accepted a methodology using coefficients where supported by the applicable contracting regime and the circumstances of the project.

It also recognised additional general expenses where those expenses represented a real cost caused by the delay.

Arbitration significance

This is particularly useful for infrastructure arbitration.

A contractor can distinguish:

Direct costs

• extra concrete;
• additional labour for changed work;
• replacement materials.

from:

Delay/prolongation costs

• site management;
• offices;
• temporary facilities;
• supervision;
• equipment standing time;
• site security;
• insurance;
• administrative personnel.

The second category is often the heart of a delay claim.

15. Case Law 7 — STS 307/2025, 26 February 2025

Delay caused by the promoter and indirect costs

Tribunal Supremo, Sala Primera, Sentencia 307/2025, 26 February 2025

This recent case concerned a construction dispute in which the contractor alleged that the promoter had caused substantial delay and sought compensation for indirect costs arising from that delay.

The claim included additional personnel and project resources that had to remain available because the works were prolonged.

Importance

The case is particularly useful for private construction arbitration because it demonstrates the continuing relevance of the distinction between:

delay caused by the contractor

and

delay caused by the employer/promoter.

It also illustrates the evidentiary problem of proving that claimed indirect costs were actually incurred rather than merely estimated.

For an arbitral tribunal, contemporaneous records can therefore be decisive:

• payroll records;
• equipment logs;
• site attendance;
• invoices;
• subcontractor records;
• insurance records;
• site-office costs;
• programme updates.

16. Case Law 8 — STS 793/2026, 24 June 2026

Delay in commencement and general expenses

A particularly recent Supreme Court decision concerns delay attributable to the Administration in commencing execution of the works.

The Court stated that where commencement is delayed for reasons attributable to the Administration, the contractor may claim compensation for the resulting damage. It also accepted that increased general expenses may, in appropriate circumstances, be quantified by applying a percentage to the project budget, provided that the existence of the damage is established and direct calculation is practically impossible.

Importance for arbitration

This is important because it shows the continuing development of Spanish jurisprudence toward a distinction between:

proof of entitlement

and

method of quantification.

A percentage-based methodology is not automatically invalid.

But the claimant must first establish that:

1. compensable delay occurred;
2. it was attributable to the opposing party;
3. actual economic damage resulted;
4. the percentage is a reasonable method of quantifying that damage.

17. Case Law 9 — STS 268/2026, 5 March 2026

The Supreme Court's 2026 jurisprudence also illustrates the other side of the equation: unsupported delay-cost claims may fail.

The Court emphasised the contractor's burden to properly establish the claimed economic detriment. Claims for indirect costs, general expenses and loss of profit can be rejected where the contractor cannot demonstrate an objectively identifiable economic loss.

This is a crucial warning for arbitration.

The proposition is:

Entitlement to compensation does not eliminate the requirement to prove the amount.

18. Delay analysis methodology in Spanish arbitration

A sophisticated arbitral tribunal will normally benefit from a structured delay analysis.

Step 1 — Establish the baseline programme

Identify:

• contractual commencement;
• contractual completion;
• contractual milestones;
• planned sequencing;
• critical path;
• float.

Step 2 — Establish actual progress

Use:

• daily reports;
• monthly progress reports;
• payment certificates;
• photographs;
• inspection records;
• correspondence;
• programme updates.

Step 3 — Identify delay events

For example:

Step 4 — Determine criticality

The tribunal should determine whether each event actually affected the contractual completion date.

Step 5 — Attribute responsibility

Each delay event should be classified as:

• employer risk;
• contractor risk;
• neutral/excusable event;
• concurrent delay.

Step 6 — Quantify the financial consequences

The contractor should establish the costs actually attributable to the compensable period.

19. Common categories of delay damages

A. Site overhead

Examples:

• project manager;
• site engineer;
• administrative staff;
• site office;
• communications;
• security;
• utilities.

Formula:

Monthly site overhead × compensable delay months

B. Equipment prolongation

Examples:

• cranes;
• excavators;
• generators;
• temporary plant;
• scaffolding;
• specialist equipment.

The tribunal should distinguish:

actual additional cost

from

mere depreciation or accounting allocation.

C. Labour

The contractor may claim additional personnel costs where workers were retained because of compensable delay.

Evidence may include:

• payroll;
• employment records;
• timesheets;
• site attendance;
• labour allocation records.

D. Insurance and guarantees

Extended project duration can increase:

• construction insurance;
• performance guarantee costs;
• advance-payment guarantee costs;
• financing costs.

These can be particularly easy to quantify if supported by invoices and bank records.

20. Loss of profit

Loss of profit is more difficult.

The contractor must generally demonstrate:

1. existence of the loss;
2. causal connection;
3. reasonable certainty;
4. absence of speculative assumptions.

An arbitral tribunal should be cautious about claims based solely on hypothetical alternative projects.

21. Prolongation costs versus disruption costs

These should not automatically be combined.

Prolongation

The project takes longer.

Example:

12 additional months × €100,000 monthly site overhead.

Disruption

The project remains within or close to the original duration, but inefficient working causes additional cost.

Example:

Repeated employer changes cause resequencing, remobilisation and reduced labour productivity.

Thus:

Delay ≠ disruption

and:

time impact ≠ automatically additional cost.

A well-prepared arbitration claim should separate them.

22. Time impact analysis

A typical expert report may contain:

Baseline programme

↓

Delay event

↓

Affected activity

↓

Critical-path impact

↓

Completion-date impact

↓

Compensable period

↓

Financial consequences

This provides the tribunal with a logical causal chain.

23. Documentary evidence

The strongest evidence is usually contemporaneous.

Important documents include:

Contract documents

• construction contract;
• specifications;
• employer's requirements;
• technical documents;
• bills of quantities;
• schedules.

Programme documents

• baseline programme;
• updated programmes;
• recovery programmes;
• critical-path analyses.

Site documents

• daily site reports;
• engineer's diaries;
• photographs;
• inspection records;
• meeting minutes.

Commercial documents

• invoices;
• payroll;
• equipment rental agreements;
• insurance certificates;
• guarantee costs;
• subcontractor claims.

Correspondence

• notices of delay;
• requests for information;
• variation instructions;
• requests for extensions;
• reservation-of-rights letters.

24. Importance of contractual notice provisions

Spanish construction contracts frequently contain notice requirements.

For example:

"The contractor must notify the employer within 7 days of becoming aware of an event likely to delay completion."

Failure to comply can become a major defence.

The tribunal therefore needs to determine:

• Was notice contractually required?
• What information had to be included?
• Was notice actually given?
• Was it timely?
• Did the employer waive strict compliance?
• Was the employer already aware of the event?
• Did the employer suffer prejudice?

The contractual consequences of defective notice depend heavily upon the wording of the particular contract.

25. FIDIC contracts in Spanish arbitration

International construction projects in Spain may use FIDIC forms.

Delay disputes commonly involve:

• Extension of Time;
• Employer's risks;
• Variations;
• delayed drawings;
• exceptional events;
• unforeseeable physical conditions;
• suspension;
• claims procedures.

Where a FIDIC contract is governed by Spanish law, the tribunal must reconcile:

FIDIC contractual mechanisms + Spanish mandatory law + Spanish contractual principles.

The contractual claim procedure remains extremely important.

26. Burden of proof

A contractor seeking delay damages should normally prove:

Liability

Event → responsibility of employer

Causation

Employer event → critical delay

Quantum

Critical delay → identifiable additional cost

The weakest claim is therefore:

"The project was delayed, and therefore we claim €10 million."

The stronger claim is:

"Employer instruction E-47 prevented activity A-320 from commencing on 15 March. Activity A-320 was on the critical path. The resulting 63-day extension is established by the programme analysis. During those 63 days, the contractor incurred €X in documented site overhead and €Y in equipment costs."

That is the type of causal structure an arbitral tribunal can evaluate.

27. Concurrent delay: practical arbitration approach

Where concurrent delay exists, tribunals should carefully examine the contract and applicable law rather than applying a universal formula.

A useful analytical matrix is:

This avoids the common mistake of treating every delay event as additive.

28. Penalty claims by the employer

The employer should establish:

1. contractual completion date;
2. actual completion date;
3. contractual penalty;
4. number of chargeable days;
5. absence of excusing events;
6. absence of employer-caused delay;
7. compliance with any contractual notice requirements.

For example:

120 days apparent delay

minus

40 days employer-caused delay

minus

20 days accepted extension

=

60 potentially chargeable days

If the contractual penalty is €20,000/day:

60 × €20,000 = €1.2 million

subject, of course, to the contract and applicable Spanish law.

29. Interaction between delay damages and penalty clauses

A tribunal must determine whether the agreed penalty is intended to:

• replace proof of actual damages;
• operate as a minimum payment;
• operate as a genuine pre-estimate;
• provide a specific remedy for delay.

The wording of the contract is therefore essential.

The Supreme Court's construction cases demonstrate that the tribunal should not isolate the penalty clause from the surrounding contractual framework and the factual cause of delay.

30. Expert evidence

Delay arbitration is often won or lost through expert evidence.

Two experts may reach radically different conclusions because they use different methodologies.

Employer's expert

May argue:

"The contractor was already 90 days behind before the employer's variation."

Contractor's expert

May argue:

"The employer's variation consumed the available float and pushed completion by 120 days."

The tribunal must therefore evaluate:

• baseline programme;
• programme logic;
• actual progress;
• critical path;
• assumptions;
• contemporaneous evidence;
• methodology.

31. The "but-for" test

A useful conceptual test is:

But for the employer's delaying event, would the project have finished on time?

If the answer is yes, causation is relatively strong.

If the contractor would already have completed the project 100 days late because of its own failures, the employer may argue that its 30-day delay caused no additional completion delay.

This is particularly important in concurrent-delay cases.

32. Delay damages and Article 1106 CC

Article 1106 provides the general framework for compensation encompassing:

• damnum emergens — actual loss;
• lucrum cessans — lost profit.

In construction arbitration, this can translate into:

Actual loss

• additional labour;
• equipment;
• insurance;
• financing;
• site overhead;
• security;
• temporary facilities.

Lost profit

• lost operational revenue;
• lost commercial opportunity;
• lost rental income.

The second category normally requires stronger proof because speculative damages are difficult to sustain.

33. Public versus private construction arbitration

Private project

The main framework is:

Civil Code + contract + applicable procedural/arbitration rules

Public project

The analysis additionally involves:

LCSP + administrative contracting rules + contract + relevant Supreme Court administrative jurisprudence

The distinction matters considerably.

For example, the Supreme Court's 2022 decision specifically addresses the relationship between administrative delay, risk and ventura and recoverable indirect costs.

34. Role of arbitration

Spanish construction disputes are particularly suitable for arbitration because delay disputes frequently require:

• construction engineering expertise;
• programme analysis;
• quantity surveying;
• financial analysis;
• contractual interpretation.

An arbitral tribunal can therefore combine legal and technical analysis more flexibly than a conventional litigation process.

Nevertheless, the tribunal must still apply the governing law and respect the contractual allocation of risk.

35. Recommended structure of a delay claim

A professionally prepared claim can be organised as follows:

Part I — Contract

• completion date;
• milestones;
• extension provisions;
• notice provisions;
• penalty clause.

Part II — Delay events

• event description;
• date;
• responsible party;
• contractual basis.

Part III — Time impact

• affected activities;
• critical path;
• float;
• resulting extension.

Part IV — Concurrent delay

• overlapping events;
• competing responsibility;
• net critical delay.

Part V — Quantum

• site overhead;
• labour;
• equipment;
• insurance;
• financing;
• guarantees;
• general expenses;
• loss of profit.

Part VI — Evidence

• programme;
• correspondence;
• invoices;
• payroll;
• expert reports;
• site records.

Part VII — Relief

• extension of time;
• damages;
• interest;
• costs;
• declaration regarding penalties.

36. Six core propositions emerging from the case law

The Spanish cases discussed above collectively establish several important propositions:

1. Delay must be attributed

The mere fact that completion occurred late does not automatically establish contractor liability. STS 556/2017 is particularly important here.

2. Contractual penalties require contractual and factual analysis

STS 28/2016 demonstrates the importance of the rules governing construction penalties and their possible moderation.

3. The contractual completion date must be established precisely

STS 330/2020 illustrates the importance of interpreting the contractual completion mechanism before calculating delay.

4. Actual delay damages can be recovered where causation is established

STS 202/2016 illustrates the relevance of expert evidence in quantifying economic consequences of construction delay.

5. Prolongation costs can include indirect costs

STS 1423/2022 is particularly significant: delay attributable to the Administration can generate compensable additional costs, and reasonable percentage-based methods may be used where properly justified.

6. Quantification still requires proof

The 2025 and 2026 jurisprudence demonstrates that a claimant cannot simply rely on an abstract percentage without sufficiently demonstrating the underlying economic loss.

37. Practical example

Assume a Spanish infrastructure contract provides:

Original completion: 31 December 2025

During execution:

• Employer design delay: 60 days
• Employer variation: 30 days
• Contractor procurement delay: 20 days
• Exceptional weather: 10 days
• Concurrent period: 15 days

The tribunal should not simply calculate:

60 + 30 + 20 + 10 = 120 days

Instead, it should determine:

1. which events affected the critical path;
2. which events overlapped;
3. whether the contractor's own delay would independently have delayed completion;
4. whether the weather event is contractually excusable;
5. whether the employer's variations displaced the original completion date.

Suppose the tribunal ultimately finds:

90 days compensable employer delay

and:

20 days contractor-responsible delay.

The contractor may then have a claim for:

90 days × proven daily prolongation cost

while the employer may potentially seek:

20 days × contractual daily penalty.

This illustrates why delay arbitration is fundamentally a causation exercise, not merely a calendar exercise.

38. Conclusion

Delay claims in Spanish construction arbitration require a combination of contractual interpretation, critical-path analysis, causation and rigorous quantum evidence.

The central principle is:

The party responsible for the delay should bear its contractual and legally recoverable consequences, but the claimant must establish both entitlement and the amount of the resulting loss.

The most useful Spanish authorities include STS 556/2017, STS 28/2016, STS 330/2020, STS 202/2016, STS 1423/2022, STS of 2 April 2008, STS 307/2025, and STS 793/2026. Together they cover the principal issues an arbitral tribunal is likely to encounter: imputability, contractual penalties, completion dates, abandonment, prolongation costs, indirect costs, general expenses, expert evidence and proof of economic loss.