What is Disallowed Cost
Disallowed Cost is cost that the Contractor cannot recover through the payment mechanism. Under the cost-based main options, the Contractor submits actual costs for reimbursement. The Project Manager reviews those costs against the ten categories in clause 11.2(26). Any cost that falls within one of those categories is Disallowed and deducted from the amount due.
The mechanism serves two purposes. First, it encourages specific contractual behaviours. Costs incurred because the Contractor failed to give an early warning are Disallowed, creating a direct financial incentive to comply with clause 15. Second, it prevents recovery of costs that result from the Contractor's own non-compliance, such as failing to follow procurement procedures stated in the Scope.
Disallowed Cost is not a penalty. It is a defined contractual term that determines which costs are recoverable and which are not. The distinction matters because it sets the boundary between shared risk (the pain/gain mechanism) and risk that sits entirely with the Contractor.
Why this matters commercially
On a £30 million NEC4 Option C contract, the Contractor bears 100 per cent of any Disallowed Cost. There is no sharing through the pain/gain mechanism. A single payment period with £165,000 of Disallowed Cost comes entirely from the Contractor's margin, whereas the same amount as legitimate inefficiency would be shared 50/50, costing only £82,500. The financial difference between poor records and normal commercial risk is substantial.
Which Contracts Include Disallowed Cost
Disallowed Cost applies to the four cost-based main options:
- Option C: Target contract with activity schedule
- Option D: Target contract with bill of quantities
- Option E: Cost reimbursable contract
- Option F: Management contract
Under Options A and B (priced contracts), the Contractor is paid based on completed activities or measured quantities, not actual cost. Disallowed Cost as a payment mechanism does not apply. However, when compensation events are assessed under any main option, the assessment uses Defined Cost, and costs that would be Disallowed are excluded from that assessment.
The Ten Categories of Disallowed Cost
Clause 11.2(26) lists ten categories. Each addresses a specific behaviour or risk that the contract allocates to the Contractor.
| Category | What is Disallowed | Why it exists |
|---|---|---|
| 1. Inadequate records | Cost not justified by the Contractor's accounts and records | Forces proper cost recording and substantiation |
| 2. Subcontractor overpayment | Cost which should not have been paid to a Subcontractor or supplier in accordance with its contract | Prevents passing through inflated subcontract costs |
| 3. Procurement non-compliance | Cost incurred without following an acceptance or procurement procedure in the Scope | Enforces agreed procurement discipline |
| 4. Missing early warning | Cost incurred only because the Contractor did not give an early warning which the contract required | Creates financial incentive for clause 15 compliance |
| 5. Dispute notification failure | Cost of preparing for and conducting an adjudication or tribunal with a Subcontractor or supplier, where the Contractor did not notify the Project Manager | Ensures the Project Manager has visibility of supply chain disputes |
| 6. Post-Completion Defect correction | Cost of correcting Defects after Completion | Incentivises completing work to standard before Completion |
| 7. Scope constraint non-compliance | Cost of correcting Defects caused by the Contractor not complying with a constraint stated in the Scope | Prevents recovery of self-inflicted rework costs |
| 8. Unused Plant and Materials | Cost of Plant and Materials not used to Provide the Works | Discourages over-ordering and waste |
| 9. Resources not required | Cost of resources not used to Provide the Works or not removed from the Working Areas when the Project Manager requested | Prevents charging for idle or surplus resources |
| 10. Dispute between the Parties | Cost of preparation for and conduct of an adjudication, payments to a member of the Dispute Avoidance Board, or proceedings of a tribunal between the Parties | Ensures each party bears its own dispute costs |
Category Scenarios in Practice
Category 2: Subcontractor overpayment. A subcontractor submits a monthly application for £320,000. The agreed subcontract rates only support £295,000 for the work done. The Contractor pays the full £320,000 to maintain the relationship. The £25,000 excess is Disallowed Cost — the Contractor bears it entirely outside the pain/gain mechanism.
Category 3: Procurement non-compliance. The Scope requires three competitive quotes for any plant hire above £5,000. The site team sources an 80-tonne crane from a preferred supplier without obtaining alternatives. The compliant market rate was £2,800/week; the actual hire was £3,400/week. The £600/week differential is Disallowed for the duration of the hire.
Category 5: Dispute notification failure. The Contractor enters a payment dispute with a subcontractor and incurs £18,000 in adjudication costs. The Project Manager was not notified of the dispute as required. The adjudication costs are Disallowed under category 5 — they sit outside the Defined Cost entirely.
The ten categories of NEC4 Disallowed Cost grouped by the behaviour each addresses
Scroll to see full diagram
Category 1 is the most frequently invoked. If the Contractor can't produce records to justify a cost, that cost is Disallowed regardless of whether it was legitimately incurred. Record keeping requirements under NEC4 cost-based options are substantial, and failing to maintain them creates direct financial exposure. Maintaining detailed site records that capture resource allocation, material deliveries, and Plant usage is essential for substantiating Defined Cost claims.
How Disallowed Cost Affects the Pain/Gain Mechanism
Under Options C and D, the pain/gain share mechanism compares actual cost against a target. Disallowed Cost sits outside this mechanism entirely. This is a critical distinction.
When the Contractor is inefficient, the overrun against the target is shared between the Contractor and the Client according to the share percentages in the Contract Data. If the share is 50/50 and the Contractor overspends by £100,000, the Contractor bears £50,000 and the Client bears £50,000.
Disallowed Cost works differently. The Contractor bears 100 per cent of any Disallowed Cost. There is no sharing. This creates a stronger incentive than the pain/gain mechanism alone.
Worked ExampleContract: NEC4 Option C, £30 million target, 50/50 pain/gain share
A contractor submits £8,200,000 in Defined Cost for the period. The Project Manager reviews the submission and identifies two issues. First, £120,000 of plant hire costs are not supported by delivery records or timesheets. Second, £45,000 was spent correcting a drainage defect caused by the Contractor not following a constraint in the Scope.
Both items are Disallowed under clause 11.2(26): the first under category 1 (inadequate records) and the second under category 7 (Scope constraint non-compliance).
The Contractor is paid £8,200,000 minus £165,000 Disallowed, giving £8,035,000 plus Fee. The £165,000 comes entirely from the Contractor's margin. It is not shared. It does not appear in the pain/gain calculation as a target overrun where the Client would absorb half. The Contractor absorbs all of it.
Had the same £165,000 been legitimate cost overrun rather than Disallowed Cost, the Contractor would have borne only £82,500 (their 50 per cent share) rather than the full £165,000.
Pain/gain shared overrun versus Disallowed Cost: same £165,000, double the Contractor exposure
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Gather captures daily resource records, material deliveries, and Plant usage as part of the site diary workflow. When the Project Manager reviews Defined Cost submissions, the contemporaneous evidence is already structured and auditable, reducing the risk of category 1 disallowance for inadequate records.
What Changed Between NEC3 and NEC4
Four changes are worth noting.
Removal of Project Manager discretion. NEC3 clause 11.2(25) began with "cost which the Project Manager decides." NEC4 removed these words. Disallowed Cost is now determined on an objective basis against the defined categories, not at the Project Manager's discretion. This change was significant. It means that whether a cost is Disallowed is a matter of contractual interpretation, not managerial judgement.
Supply chain dispute notification. NEC4 added a new category requiring the Contractor to notify the Project Manager of preparation for and conduct of an adjudication or tribunal with a Subcontractor or supplier. If notification is not given, those costs are Disallowed. This reflects NEC4's push for transparency in supply chain management.
Dispute Avoidance Board costs. NEC4 Option W3 introduced the Dispute Avoidance Board. Payments to DAB members are included as Disallowed Cost, ensuring the cost of dispute avoidance sits outside the reimbursable cost mechanism.
Terminology update. References to "Works Information" throughout clause 11.2(26) were replaced with "Scope," consistent with the wider NEC4 terminology changes.
Common Mistakes in Practice
Treating Disallowed Cost as a management tool for controlling inefficiency. Some Project Managers use Disallowed Cost to reduce payments where they believe the Contractor has been inefficient. This is incorrect. Inefficiency is addressed through the pain/gain mechanism, not through Disallowed Cost. The ten categories in clause 11.2(26) are specific and defined. Applying them beyond their scope undermines the contractual risk allocation that NEC4 was designed to achieve.
Failing to maintain contemporaneous records. Category 1 (inadequate records) is the most commonly invoked ground for disallowance. If cost records are compiled retrospectively at the end of a period rather than recorded daily, they are vulnerable to challenge. The standard of "justified by the Contractor's accounts and records" requires records that are contemporaneous, detailed, and consistent with the Schedule of Cost Components.
Accepting bespoke amendments without understanding the consequences. Clients frequently add bespoke categories to clause 11.2(26), such as "cost not properly incurred" or "cost arising from a failure by the Contractor to comply with the terms of this contract." These broad additions shift the risk balance significantly and can be used to disallow costs far beyond the ten standard categories. Contractors should identify and price these amendments at tender stage, not discover them during cost reviews.
Ignoring the early warning connection. Category 4 Disallows cost incurred because the Contractor failed to give an early warning. This interacts with clause 63.7, which reduces compensation event assessments for the same failure. The two mechanisms are separate, but both create financial consequences for the same behaviour. A Contractor who fails to give an early warning faces a potential reduction in their CE assessment under clause 63.7 and a potential disallowance of costs that would not have been incurred had the early warning been given.
Double jeopardy risk. Missing an early warning can trigger both clause 63.7 (the Project Manager reduces the CE assessment by the cost that could have been avoided) and clause 11.2(26) category 4 (the cost itself is Disallowed). On a single event, this can mean losing the entitlement twice — once through a reduced CE assessment, and again through the Disallowed Cost mechanism. The only defence is a functioning early warning register reviewed weekly.
Missing the time bar connection. Contractors who fail to notify compensation events within eight weeks lose the right to claim additional Defined Cost for that event. If the cost has already been incurred, the Contractor cannot recover it through the CE mechanism, and the Project Manager may also challenge the cost under the Disallowed Cost categories. Poor notification discipline compounds poor record keeping.
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