NEC4 Disallowed Cost Explained: The Clause 11.2(26) Categories and How to Avoid Deductions

Disallowed Cost is a direct test of commercial control under NEC4 ECC. Under Options C, D, E and F, the Contractor must demonstrate that cost was properly incurred, contractually compliant, supported by records and necessary to Provide the Works.

The consequence is practical: a cost that is disallowed is not reimbursed. Under target-cost options, it can also reduce the Contractor’s share and ultimately affect profit.

This is the fourth instalment in our NEC4 series, following Early Warnings, Compensation Events and the related principles of payment under construction contracts.

Where Disallowed Cost sits in NEC4 ECC

Four main options. One central control principle.

Disallowed Cost is defined at clause 11.2(26) of the NEC4 Engineering and Construction Contract.

It is relevant to the cost-based payment mechanisms under:

• Option C – Target Contract with Activity Schedule;
• Option D – Target Contract with Bill of Quantities;
• Option E – Cost Reimbursable Contract; and
• Option F – Management Contract.

Under these options, the amount due is based on Defined Cost, subject to the relevant Fee provisions. Disallowed Cost is excluded from the amount assessed as Defined Cost.

In practical terms:

Defined Cost less Disallowed Cost, plus Fee, determines the reimbursable cost position.

Under target options C and D, the effect extends beyond the immediate payment assessment. Lower Defined Cost can affect the Price for Work Done to Date, the target-cost outturn and the Contractor’s share.

Options A and B operate differently. Option A is based primarily on the Activity Schedule and Option B on the Bill of Quantities. The Contractor generally carries the risk that its actual cost will be higher than the priced amount. Disallowed Cost is therefore not the normal mechanism for assessing routine payment under those options.

Defined Cost may still be relevant to the assessment of compensation events under Options A and B, subject to the applicable Short Schedule of Cost Components and Contract Data. The distinction should therefore be kept clear: Disallowed Cost is principally a payment control under the cost-based options, not a universal deduction mechanism for every NEC4 contract.

The clause 11.2(26) categories

The definition should be read with the complete contract, including the Scope, Contract Data, selected secondary options and any Z clauses. Some employers amend or expand the standard wording.

Category	Plain-English meaning	Practical example
Cost not justified by accounts and records	The Contractor cannot demonstrate that the cost was incurred, relates to the contract and is properly supported.	Labour charged without timesheets, plant costs without utilisation records, or invoices that cannot be reconciled to the work.
Payment not made to a Subcontractor or supplier in accordance with its contract	The Contractor cannot pass through a payment that should not have been made under the relevant subcontract or supply agreement.	Paying for quantities, rates or work that were not due under the subcontract.
Failure to follow an acceptance or procurement procedure in the Scope	Additional cost incurred only because a stated approval, tendering or procurement process was ignored.	Ordering specialist equipment without the acceptance required by the Scope, resulting in an avoidable premium.
Failure to give a required early warning	Cost incurred only because the Contractor failed to notify a matter that should have been raised under the early-warning process.	Continuing with an inefficient sequence when an early warning could have allowed the parties to agree a lower-cost mitigation.
Certain adjudication or tribunal costs	Costs associated with specified proceedings may be disallowed where the required notification to the Project Manager was not given.	Preparing for a subcontractor adjudication without notifying the Project Manager as required by the contract.
Correction of Defects after Completion	The cost of correcting a Defect after Completion is not reimbursable as Defined Cost.	Returning after Completion to rectify defective installation or incomplete remedial work.
Defects caused by failure to comply with the Scope	Rework caused by ignoring a stated constraint on how the works must be provided is disallowed.	Using an unapproved method or material that creates a defect requiring correction.
Plant and Materials not used to Provide the Works	Surplus or unused items are not generally recoverable, subject to reasonable wastage and the effect of a Scope change.	Over-ordering materials or bringing plant to site that is not used for the works.
Resources not used or not removed when instructed	Costs for unused resources, allowing for reasonable availability and utilisation, or resources left in the Working Areas after instruction to remove them, may be disallowed.	Keeping idle plant or personnel on site without a justified requirement after the Project Manager has requested removal.

The test is not that every cost must be perfectly efficient. NEC4 allows for reasonable wastage, availability and utilisation. The issue is whether the cost falls within the contractual definition and whether the Contractor can demonstrate why it was incurred.

A simple disallowed-cost decision flow

The following decision sequence can be used during weekly cost reviews and payment preparation:

Candidate cost incurred
          |
          v
Is the cost supported by accounts and records?
          |
       No |--------------------> DISALLOWED
          |
         Yes
          |
          v
Were the required Scope, acceptance and procurement procedures followed?
          |
       No |--------------------> DISALLOWED
          |
         Yes
          |
          v
Was a required early warning given?
          |
       No |--------------------> DISALLOWED
          |
         Yes
          |
          v
Was the plant, material or resource used to Provide the Works?
          |
       No |--------------------> DISALLOWED
          |
         Yes
          |
          v
ALLOWED AS DEFINED COST

This is a management screening tool, not a substitute for reviewing the precise contract wording. It should be supplemented by checks on defects, subcontractor payments, dispute notifications and any project-specific amendments.

Why the commercial consequences matter

Disallowed Cost is not simply an accounting adjustment made at the end of a reporting period.

Under Options C, D, E and F, it can reduce the amount certified or reimbursed through the payment mechanism. Under target options, repeated deductions can also affect the final outturn against the target and the Contractor’s share.

The effect can be illustrated simply:

Item	Amount
Candidate Defined Cost	£10.00m
Disallowed Cost	(£0.25m)
Allowable Defined Cost	£9.75m
Fee applied under the contract	Added in accordance with Contract Data
Commercial consequence	Lower reimbursable cost and potential share impact

The precise assessment depends on the option, the Contract Data and the applicable cost component. However, the principle remains the same: weak records, procedural non-compliance and avoidable expenditure reduce the cost that can be recovered.

Repeated deductions also provide evidence about the quality of the project’s controls. They may indicate:

• unreliable cost capture;
• weak subcontract administration;
• poor procurement governance;
• ineffective early-warning discipline;
• inadequate plant and resource planning;
• unresolved quality issues; or
• insufficient integration between delivery and commercial teams.

That can damage credibility in payment discussions and board-level reporting, even where individual deductions are relatively modest.

How to avoid Disallowed Cost

1. Maintain contemporaneous, audit-ready records

Every material cost should be capable of being traced from source evidence through the cost report and into the payment assessment.

Depending on the cost category, this may include:

• timesheets and allocation records;
• plant and Equipment logs;
• delivery tickets and goods-received records;
• invoices and payment certificates;
• subcontract accounts and valuations;
• site diaries and progress records;
• photographs and inspection records;
• procurement approvals;
• instructions and correspondence; and
• reconciliations between forecast, ledger and Defined Cost.

Records assembled months after the event are more difficult to validate and more vulnerable to challenge. The control should operate when the cost is incurred, not when the assessment is prepared.

2. Follow the Scope’s procedures precisely

Acceptance and procurement procedures are contractual controls, not administrative preferences.

The commercial team should maintain a register of:

• required submissions;
• acceptance criteria;
• approval responsibilities;
• procurement thresholds;
• tendering requirements;
• agreed suppliers;
• required lead times; and
• outstanding decisions.

Where compliance is not possible, the issue should be escalated promptly. Proceeding without the required approval and attempting to explain the decision retrospectively creates avoidable disallowance risk.

3. Give early warnings rather than staying silent

An early warning costs nothing to issue and can protect cost recovery.

Under clause 15, the Contractor and Project Manager notify matters that could increase the Prices, delay Completion or a Key Date, or impair performance. Clause 11.2(26) creates a further commercial reason to comply: cost incurred only because a required early warning was not given may be disallowed.

The warning should identify the matter, potential effect, evidence available, proposed mitigation and decision required. It should not be held until the cost has crystallised.

For more detail, see the NEC4 Early Warnings guide.

4. Control plant, materials and resources

Resource planning should be connected to the programme and cost forecast.

Project teams should regularly test:

• whether plant remains necessary;
• whether materials ordered are required for the current Scope;
• whether surplus materials can be returned or redeployed;
• whether personnel are being productively utilised;
• whether standby is justified;
• whether resources should be removed from the Working Areas; and
• whether a Scope change has caused unused resources.

A resource can be available without being unnecessarily idle. The evidence should explain the operational requirement and the period for which that availability was reasonable.

5. Manage defects before Completion

Defects should be identified, allocated, corrected and closed through a controlled process.

The objective is not only quality compliance. It is also to prevent remedial work becoming a post-Completion cost that cannot be recovered. Where a defect results from failure to comply with a Scope constraint, the associated correction may also be disallowed.

The quality, programme and commercial teams should therefore share information on:

• outstanding defects;
• planned correction dates;
• access requirements;
• responsible parties;
• evidence of closure; and
• residual cost exposure.

6. Make the risk visible in the forecast

Disallowed Cost risk should appear in the commercial forecast rather than being hidden within unexplained variances.

A useful management view separates:

• actual deductions already identified;
• costs under review;
• potential deductions not yet assessed;
• corrective actions;
• responsible owners; and
• expected financial exposure.

This enables senior stakeholders to distinguish between a one-off documentation issue and a systemic control failure.

Disallowed Cost, compensation events and delay damages

These concepts are frequently confused, but they address different questions.

Issue	Main question	Typical effect
Disallowed Cost	Does this incurred cost qualify as reimbursable Defined Cost under the contract?	Deduction from Defined Cost and possible reduction in payment, share or profit.
Compensation event	Has a contractual event changed the Prices, Completion Date or Key Dates?	Assessment using the applicable contract mechanism, generally including Defined Cost and Fee.
Delay damages	Has the Contractor failed to meet Completion or another relevant contractual date, creating liability under the contract?	A separate contractual charge or deduction, subject to the conditions and provisions of the contract.

A compensation event does not automatically make every related cost recoverable. The cost must still satisfy the relevant Defined Cost provisions and must not be Disallowed Cost.

Equally, Disallowed Cost is not delay damages. A Contractor may incur disallowed cost without delaying Completion, and delay damages may arise from delay without any disallowed cost being identified.

Final controls for commercial teams

A robust NEC4 payment process should ask five questions before each assessment:

1. Can every material cost be justified through contemporaneous accounts and records?
2. Were the Scope’s acceptance and procurement procedures followed?
3. Were early warnings issued when required?
4. Were plant, materials and resources used, justified or removed appropriately?
5. Are defects, subcontractor disputes and potential deductions visible in the forecast?

The strongest control environment links the cost ledger, programme, procurement records, Early Warning Register, defect log and payment assessment. This creates a consistent evidence trail from delivery activity to commercial outcome.

Disallowed Cost is therefore a measure of contract administration as much as cost. Disciplined records, timely notification, procedural compliance and active resource management protect cash, forecast integrity and confidence at the highest levels of scrutiny.

Sources and references

• NEC4 Engineering and Construction Contract
• NEC: The use and abuse of Disallowed Cost
• NEC: Disallowed Cost and the cost of subcontractor disputes in NEC4 ECC
• NEC: Disallowed costs : how to avoid the contractual and commercial pitfalls
• NEC4 ECC clause 11.2(26)
• NEC4 ECC Schedule of Cost Components and relevant Contract Data
• NEC guidance on Defined Cost, Disallowed Cost and resource assurance

Social-sharing summary

Disallowed Cost under NEC4 ECC clause 11.2(26) can directly reduce reimbursement, target performance and Contractor share. This practical guide explains the main categories, the difference between Disallowed Cost, compensation events and delay damages, and the controls needed to protect cost recovery.

---

About the Author

Nick Garvey is a chartered construction professional (MCIOB, FCaSA, FQSi) with more than 25 years of experience in commercial leadership and project controls across defence infrastructure, government estates, highways, facilities management and public-sector programmes. He leads cost, schedule, risk and performance reporting on major defence infrastructure programmes, chairs risk reviews at senior governance level, and writes about earned value management, quantitative risk analysis, NEC4 contracts and forecast integrity.

All views my own, shared in a personal capacity.