7 JCT & NEC4 Contract Clauses Every Main Contractor Must Red-Line

Main contractors in the UK sign dozens of subcontracts every year — JCT Design and Build, NEC4 Engineering and Construction Subcontract, bespoke amendments layered on top of both. Most project managers read the headline figures: contract sum, programme dates, retention percentage. The clauses that actually drive disputes and cost overruns get skimmed or missed entirely. By the time a payment notice is rejected or a compensation event is time-barred, it's too late to negotiate.

This article identifies the seven clauses that consistently cause the most financial damage to main contractors, with specific language to challenge before you put pen to paper. As we covered in our guide to avoiding costly contract gaps, the cost of a missed clause rarely shows up until the worst possible moment — mid-project, under programme pressure, with a disputed variation in hand.

1. Pay-When-Paid and Conditional Payment Clauses

The Housing Grants, Construction and Regeneration Act 1996 (as amended by the Local Democracy, Economic Development and Construction Act 2009) prohibits pay-when-paid clauses in most construction contracts. Yet developers and employers still attempt to insert conditional payment language that achieves the same effect. Watch for phrases that tie your payment obligation to receipt of funds from a third party — even if the word "when" is absent.

This clause is unenforceable under the 1996 Act unless the employer is insolvent. Red-line it and replace with a fixed payment period tied to your own due date, not the employer's payment cycle. A compliant alternative links payment to the issue of your own payment notice under the subcontract.

2. Notification Windows for Compensation Events (NEC4)

Under NEC4, Clause 61.3 requires the contractor to notify a compensation event within eight weeks of becoming aware of it. Miss that window and you lose your entitlement to additional time and money — regardless of how legitimate the event is. On a complex civils project worth £4.5 million, a missed eight-week notification for a utilities diversion can wipe out £80,000 to £120,000 in legitimate additional cost.

Employers and their project managers sometimes add bespoke Z-clauses that shorten this window further — to four weeks or even 14 days. Challenge any Z-clause that reduces notification periods below the NEC4 standard. Your commercial team must have a live register of potential compensation events from day one on site.

3. Liquidated Damages Set Without Genuine Pre-Estimate

JCT contracts require liquidated and ascertained damages (LADs) to represent a genuine pre-estimate of the employer's loss. In practice, employers frequently insert LADs that bear no relation to actual loss — £15,000 per week on a £600,000 fit-out contract, for example. Before signing, request the employer's basis of calculation. If they cannot produce one, the LADs may be unenforceable as a penalty under Cavendish Square v. Makdessi [2015]. Red-line any LAD rate that exceeds 1.5% of the contract sum per week without documented justification.

4. Retention Release Tied to Employer Milestones

Standard JCT SBC/Q 2016 releases half of retention on practical completion and the remainder at the end of the rectification period. Bespoke amendments increasingly tie the second release to the employer's final account settlement with the client — events entirely outside your control that can delay retention release by 18 to 36 months. On a £2.8 million subcontract at 3% retention, that's £42,000 sitting in someone else's account with no clear release date. The Building Safety Act 2022 introduced provisions for retention deposit schemes on higher-risk buildings; check whether your project falls within scope and whether the employer has complied. Red-line any clause that decouples retention release from your own rectification period completion.

5. Design Liability Scope Creep in JCT Design and Build

JCT DB 2016 Clause 2.17 limits the contractor's fitness-for-purpose obligation to reasonable skill and care unless the contract expressly states otherwise. Employers regularly attempt to impose absolute fitness-for-purpose liability through Employer's Requirements or bespoke amendments — language that professional indemnity (PI) insurers will not cover. As detailed in our post on contract clauses every GC should red-line, fitness-for-purpose exposure is one of the most common uninsured risks in design-and-build procurement. Red-line any clause that uses the words "fit for purpose," "fit for intended use," or "guarantee" in the context of design liability, and replace with "reasonable skill and care in accordance with the standard of a competent contractor."

6. Adjudication Notice Restrictions

The 1996 Act gives any party to a construction contract the right to refer a dispute to adjudication at any time. Bespoke amendments sometimes attempt to restrict this right — requiring internal escalation procedures, mandatory mediation periods, or board-level sign-off before a notice of adjudication can be served. These restrictions are generally unenforceable under the Act, but they create procedural uncertainty that delays your ability to recover money. Red-line any clause that imposes pre-conditions on adjudication referral. The statutory right to adjudicate must remain unconditional.

7. Entire Agreement and No Oral Variation Clauses

NEC4 and JCT contracts both contain entire agreement provisions — these are standard and broadly acceptable. The risk arises when employers add "no oral variation" clauses that go further than the Supreme Court's position in Rock Advertising v. MWB Business Exchange [2018]. If your site team agrees a variation verbally and the clause bars recovery, you absorb the cost. Red-line any clause that prevents written confirmation of verbal instructions from being issued retrospectively, and ensure your subcontract includes a clear instruction mechanism — NEC4 Clause 13 or JCT Clause 3.10 — that your supervisors are trained to use on day one.

Understanding how these clauses interact with your procurement process matters too. If you're tendering subcontract packages before finalising your own head contract terms, the risk of misaligned flow-down provisions is significant — something we explored in depth in our guide to AI in construction contract risk management.

The bottom line

Every one of these seven clauses has featured in UK adjudications or TCC proceedings in the last five years. They are not theoretical risks — they are the specific mechanisms by which main contractors lose money on otherwise well-managed projects. The window to challenge them is narrow: once you've signed, your leverage disappears and your only remedy is dispute resolution, which costs time and money regardless of outcome.

Build a red-line checklist into your subcontract award process. Before any contract worth more than £150,000 is executed, every clause in this list should have been reviewed, challenged where necessary, and either amended or accepted with documented commercial awareness. That discipline — applied consistently across your supply chain — is what separates contractors who manage risk from those who absorb it.