The JCT Design and Build Contract 2024: A Client's Guide
The JCT Design and Build Contract (DB 2024) is the standard UK building contract for projects where one contractor designs and builds the works for a lump sum. The client (the "Employer") sets out what it wants in the Employer's Requirements, the contractor answers with its Contractor's Proposals, and the contractor then takes responsibility for completing the design and building it, with payment in stages or monthly instalments. The 2024 edition, published by the Joint Contracts Tribunal on 17 April 2024, replaced DB 2016.
It's the contract most London developers and occupiers sign for a design and build project. Most of them also amend it.
How the contract fits together
| Document | Who writes it | What it does |
|---|---|---|
| Articles of Agreement | Both parties | Names the parties, the Employer's Agent, the principal designer and principal contractor, and the contract sum |
| Contract Particulars | Both parties | The project's settings: dates, liquidated damages, payment method, insurance option, retention, rectification period |
| Employer's Requirements | The client and its design team | What must be built, to what standard, with what level of design already done |
| Contractor's Proposals | The contractor | How the contractor will meet the requirements |
| Contract Sum Analysis | The contractor | Breakdown of the lump sum, used for valuing changes and stage payments |
| Conditions | JCT standard text | The rules on design, time, money, quality, insurance, termination and disputes |
The Employer's Requirements are the most important document you write. Anything they leave vague, the contractor will price and design to the cheapest compliant answer. Anything they over-specify, you pay for, including design risk you meant to pass on.
Who carries design responsibility
Under DB the contractor completes the design and is responsible for it. The standard form sets the contractor's design liability at the same level as an independent professional designer: reasonable skill and care, not an absolute "fitness for purpose" promise. Many clients amend that, and contractors price the amendment.
Two points catch clients out:
- Design already done by your team. If your architect has taken the design to an advanced stage before the contractor is appointed, the contract needs to say clearly who is responsible for that design. The standard form doesn't automatically make the contractor check and adopt it.
- Novation. It's common practice to "novate" the client's architect and engineers to the contractor, so the same designers carry on under the contractor. It keeps design continuity, but your former designers now work for the contractor.
Payment, retention and the contract sum
DB is a lump sum contract. The contractor is paid in interim payments, either by agreed stages or periodically (usually monthly), as set in the Contract Particulars. Each interim payment follows the Construction Act regime: a due date, a payment notice, a final date for payment and the right to issue a pay less notice.
A retention percentage is held back from each payment and released in two halves: at practical completion and at the end of the rectification period, once defects are made good. The percentage, the rectification period and the liquidated damages rate are all set in the Contract Particulars, so they are yours to negotiate.
Changes (variations) are valued using the Contract Sum Analysis where it applies. If you expect to change the scope, ask for a properly broken-down analysis at tender; it's your best protection when a change is priced.
Time: extensions and liquidated damages
The contractor must complete by the completion date or pay liquidated damages at the agreed rate. It can claim an extension of time for "Relevant Events" (causes outside its control listed in the contract) and money for "Relevant Matters".
The 2024 edition changes this in several ways:
- The Employer now has 8 weeks, down from 12, to decide on an interim extension of time.
- Epidemics are a new Relevant Event.
- The change in law event is wider, and covers changes that directly affect the works.
- "Statutory Undertakers" are renamed "Statutory Providers".
- The old antiquities clause now also covers asbestos, contaminated material and unexploded ordnance found on site.
That last point matters in London. Older buildings and brownfield sites routinely turn up asbestos and contamination, and you should decide in the contract who carries that risk, rather than discover it on the first day of strip-out.
What changed in DB 2024: summary
| Area | DB 2016 | DB 2024 |
|---|---|---|
| Notices | Mostly by post or hand | Most notices by email; key default and termination notices by email only if the parties opt in |
| Interim extension of time decision | 12 weeks | 8 weeks |
| Epidemics | Not a Relevant Event | New Relevant Event |
| Asbestos, contamination, UXO | Not expressly covered | Within the antiquities provision |
| Building Safety Act | Not reflected | Part 2A dutyholder duties; new Article naming principal designer and principal contractor |
| Collaborative working | Optional supplemental provision | Article: act in good faith and in a spirit of trust and respect |
| Sustainability | Optional | Main conditions: contractor to suggest economically viable environmental improvements and give environmental information on materials on request |
| Disputes | Negotiation optional | Clause 9.1: prompt notice of likely disputes and senior executives meet to negotiate, without affecting the right to adjudicate |
| Insolvency | Older grounds | New grounds under the Corporate Insolvency and Governance Act 2020 |
| Fluctuations | Printed in the contract | Published on the JCT website; Option A schedule removed from DB |
The JCT's own view is that the changes don't materially shift risk between the parties. They do change the administration, so your Employer's Agent and the contractor's team need to work to the 2024 rules, not habit.
Building Safety Act duties in the contract
Since the Building Safety Act 2022, Part 2A of the Building Regulations 2010 puts duties on clients, designers and contractors. DB 2024 reflects that: a new Article records who is appointed principal designer and principal contractor for Building Regulations purposes, both parties must comply with their Part 2A duties, and the Employer must provide the building information the regulations require. Failing to comply is a ground for termination by either side.
Higher-risk buildings (generally 18 m or seven storeys and above, with at least two residential units) bring a separate approval regime that the standard form doesn't specifically address. If your scheme is one, expect bespoke amendments. Our guide to Gateway 2 and second staircases explains the regime.
Common amendments clients ask for
These are negotiated deal by deal. Each moves risk, and each has a price.
- A stronger design obligation, sometimes up to fitness for purpose.
- Contractor responsibility for the client's pre-contract design, after checking it.
- Novation of the client's design team.
- Collateral warranties for funders, purchasers and tenants.
- Specific allocation of ground, contamination and existing-structure risk.
- Tighter limits on what counts as a Relevant Event.
A contractor who agrees to everything without changing the price either hasn't read the amendments or plans to recover the cost in claims.
When DB is the right contract
DB suits clients who want one party responsible for design and construction, one lump sum and one point of contact. It works best when the brief is settled before the contract is signed. If the design is still moving, an early-stage pre-construction services agreement followed by DB lets the contractor help develop the design before the price is fixed.
At Medusa in Knightsbridge, we were brought in at RIBA Stage 2 with a concept the budget couldn't support, and adapted the design until the vision and the budget matched. The 180 m² spa and beauty clinic was then designed and built across four floors in 17 weeks. That's the design and build case in one example: one team, one budget, decisions made where they're cheapest.
The bigger choice between design and build and the traditional route is covered in design and build vs traditional procurement. The client-side role that runs the contract day to day is explained in our guide to the Employer's Agent.
Before you sign a JCT DB contract
- Employer's Requirements complete, with clear performance standards.
- Responsibility for any pre-contract design written in.
- Payment method, retention, rectification period and liquidated damages set in the Contract Particulars.
- Asbestos, contamination and existing-structure risk allocated.
- Principal designer and principal contractor named.
- Contract Sum Analysis detailed enough to value changes.
- Collateral warranties agreed for funders and tenants.
- Employer's Agent appointed and briefed on the 2024 notice rules.
We work as a design and build contractor, and as client-side construction project managers when a client wants someone to run the contract for them.
Planning a design and build project in London? Send us the address and the brief, and we'll tell you how we'd deliver it.
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