If you are a UK subcontractor, the ground beneath your feet just shifted. Main contractors are rapidly phasing out the older JCT 2016 suites and rolling out the new JCT 2024 Sub-Contract Conditions.
While a lot of the standard boilerplate looks the same, hidden deep within the new templates are major structural timeline changes. If you don’t know how to navigate these updates, you risk losing your rights to extensions, swallowing massive delay penalties, and completely blowing your trade margins.
As specialists in translating complex legal jargon into plain English, we have deconstructed the new text. Here are the three non-negotiable updates you must understand before signing your next project.
1) The 10-Week Trap: Main Contractors Are on a Shorter Lease
The single biggest change in the JCT 2024 Sub-Contract framework impacts how Extensions of Time (EOT) are assessed.
Under the old JCT 2016 rules, if you submitted a delay notice, the main contractor had a relatively comfortable 16 weeks to review, respond, and grant or deny your request.
The JCT 2024 Update: Main contractors now have just 10 weeks from the date you provide full particulars to assess and give their decision on an EOT.
Why this is a double-edged sword for trades:
The Good: It prevents main contractors from sits on your request for 4 months, leaving you completely in the dark while liquidated damages accumulate.
The Danger Zone: Because main contractors are facing a tighter turnaround, they are highly likely to reject incomplete or poorly documented applications immediately just to protect their own liabilities.
Your Playbook: Your substantiation must be bulletproof from day one. If you encounter a delay, you cannot afford to slowly drip-feed evidence over several weeks. Submit complete records of the delay instantly.
2) Expanded “Relevant Events”: New Protection for Subcontractors
It isn’t all bad news. JCT 2024 introduces explicit new protections regarding what actually qualifies as a Relevant Event—the legal triggers that excuse you from project delay penalties.
Historically, if you hit an unexpected ground or site condition, arguing for an extension under a standard JCT sub-contract was an uphill battle that often required expensive legal intervention. JCT 2024 modernises this by expanding the list of events.
The updated contract suite now explicitly includes protections for:
Asbestos Discovery: Halting work due to unexpected asbestos on site is now explicitly covered.
Contaminated Land: Encountering unexpected toxic or hazardous soil conditions.
Unexploded Ordnance (UXO): Finding historical war ordnance or unexploded bombs during excavation.
Epidemics & Regulatory Changes: Refined language to deal with post-pandemic realities and sudden changes in UK construction laws.
If your work is derailed by any of these elements, the contract now explicitly backs your claim for a timeline extension.
3) Collaborative Working & Asbestos Liabilities
Beyond schedules and events, JCT 2024 pushes a massive cultural change: The duty to collaborate. The new terms explicitly require both parties to act in good faith, communicate transparently, and flag potential disputes early before they turn into full-scale legal battles.
Furthermore, liability caps around environmental hazards—specifically relating to the expanded “Relevant Events” noted above—mean that if you follow proper notice procedures, the financial risk of these specific disruptions moves away from your shoulders and onto the employer or main contractor.
The Golden Rule for 2024 Project Transitions
While JCT 2024 offers better legal protections for site issues, it demands absolute administrative discipline. If your internal paperwork is disorganised, main contractors will weaponise the strict new 10-week assessment window to shut down your claims.
Working under a new 2024 draft? Use my contract checker on Trade Contracts Simplified to ensure your payment timelines haven’t been quietly squeezed and your liability exposure remains protected.
Are you a specialist trade? Read my full Defending Your Final Account – A Fire & Security Subcontractor’s Guide to JCT Variations to see how these site disruptions threaten your final account values.