Ask any employer why they chose design and build over a traditional route, and you'll usually get the same answer: one contractor, one point of responsibility, one number to hold them to. The JCT Design and Build Contract is the standard form that delivers exactly that in the UK market, and it is one of the most widely used JCT contracts on commercial, residential and industrial projects of every scale.
This guide explains how the JCT Design and Build Contract actually work: what the Employer's Requirements and Contractor's Proposals do, how design risk is split between the parties, how payment and the Employer's Agent role function day to day, and what changed when JCT released its 2024 edition. You'll also find a comparison table against JCT's traditional Standard Building Contract, a risk-allocation graphic, and answers to the questions QSs and commercial managers ask most often about this form.
Whether you're administering a live design and build project, preparing to advise an employer on which JCT form to select, or revising for the APC Contract Practice competency, this article covers the structure, terminology and practical mechanics that matter in the cost office and on site.
By the end, you'll understand exactly where design liability sits, how the payment cycle runs, and why getting the Employer's Requirements right at tender stage matters more on this form than almost any other decision in the procurement process.
Quick Answer
The JCT Design and Build Contract (JCT DB) is a standard form construction contract published by the Joint Contracts Tribunal in which the contractor takes on responsibility for both designing and constructing the works, in return for a lump sum. The employer sets out its brief in the Employer's Requirements; the contractor responds with the Contractor's Proposals, which become the basis of the design the contractor is contractually bound to deliver. There is no independent contract administrator - a JCT DB project is instead run by an Employer's Agent, who certifies payment and administers the contract on the employer's behalf.
What Is the JCT Design and Build Contract?
The JCT Design and Build Contract sits within the wider JCT suite of standard forms produced by the Joint Contracts Tribunal, the body representing employers, contractors, consultants and specialists across UK construction. Unlike the JCT Standard Building Contract, where the employer's design team (architect, structural engineer, services engineer) produces a complete design that the contractor simply prices and builds, JCT DB transfers design responsibility to the contractor alongside the build responsibility. This is often described as 'single point responsibility' - the employer has one party to deal with if something goes wrong, rather than trying to work out whether a defect originated in the design or the construction.
Where design and build sits in the JCT family
JCT publishes several contracts that involve an element of contractor design, including the Design and Build Contract, the Intermediate Building Contract with contractor's design, and the Minor Works Building Contract with contractor's design. The full JCT DB form is intended for larger, more complex projects where the contractor is taking on complete design responsibility for the works, rather than a discrete design element bolted onto an otherwise traditionally designed building. As RICS guidance notes, where a contractor is only designing a limited part of the works rather than completing the design for the whole project, a different JCT form - not the full Design and Build Contract - should generally be used.
- Single contract, single point of contact for design and construction
- Lump sum pricing based on the Contractor's Proposals and Contract Sum Analysis
- No independent contract administrator - the Employer's Agent runs the contract
- Widely used for commercial, industrial, residential and fit-out projects
- Available with sectional completion, and via a two-stage or single-stage tender route
Employer's Requirements and Contractor's Proposals
The two documents that define what actually gets built under a JCT DB contract are the Employer's Requirements (ER) and the Contractor's Proposals (CP). Get these wrong at tender stage, and the consequences ripple through the entire project, so understanding what each one does - and does not - cover is essential for any QS working on a design and build scheme.
Employer's Requirements
The Employer's Requirements set out what the employer wants: the brief, performance standards, specification requirements, planning constraints, programme dates and any design work already carried out before novation to the contractor. On a small fit-out this might run to a handful of pages; on a major commercial development it can extend to dozens of specification documents and drawings built up over months by the employer's professional team. The more precisely the ER are drafted, the less scope there is for the contractor to interpret gaps in its own favour later in the project.
Contractor's Proposals
The Contractor's Proposals are the contractor's response - its solution to the brief, including concept design, technical specification, and the Contract Sum Analysis that breaks the lump sum price down by element. Once the contract is executed, the Contractor's Proposals become the benchmark the contractor must build to. Clause 2.15 of the standard form (in the 2016 and 2024 editions) confirms that, subject to limited exceptions, the contractor is not responsible for the contents of the Employer's Requirements or for verifying the adequacy of any design contained within them - which is precisely why the drafting quality of the ER matters so much to the employer's risk position.
- Any discrepancy between the ER and CP should be identified and resolved before contract execution, not after
- The Contract Sum Analysis is used to value variations and interim payments throughout the project.
- Design development after novation of consultants still sits with the contractor's design team
- Ambiguities are generally construed in the contractor's favour once the contract is signed.
Design Risk and Liability Under JCT DB
The headline attraction of design and build for employers is risk transfer - but it is not unlimited, and QSs need to understand exactly where the boundary sits. The contractor takes on responsibility for completing and coordinating the design, and for the fitness of that design for its intended purpose in most cases, but liability is not absolute.
Table 01 / Risk allocation
Who carries the risk under JCT Design and Build
| Risk area | Sits with | Notes |
|---|---|---|
| Design completion and coordination | Contractor | Contractor completes and coordinates design from the Employer's Requirements |
| Adequacy of Employer's Requirements | Employer | Contractor not liable for ER content under clause 2.15 |
| Pre-construction site information | Shared | Depends on surveys provided and disclaimers in the ER |
| Ground conditions / contamination | Negotiated | Now an express Relevant Event in DB 2024 alongside asbestos and UXO |
| Fitness for purpose of the design | Contractor | Unless amended down to reasonable skill and care, often via collateral warranty terms |
| Programme and completion date | Contractor | Subject to extension of time for Relevant Events |
Source: JCT Design and Build Contract 2016/2024 conditions; RICS and legal commentary on clause 2.15 risk allocation.
One point that regularly catches out less experienced commercial teams: fitness for purpose is a stricter standard than the 'reasonable skill and care' duty owed by a traditional design consultant, and it can create professional indemnity insurance complications for the contractor's design consultants. As a result, it is common - though not automatic - for employers to accept a contract amendment capping the contractor's design liability at reasonable skill and care rather than strict fitness for purpose, to keep PI cover intact down the supply chain.
The Employer's Agent Role
Because JCT DB has no independent contract administrator equivalent to the architect or contract administrator under a traditional JCT form, the employer appoints an Employer's Agent to run the contract on its behalf. This role is very often filled by a quantity surveyor or a project manager with a commercial background, which makes it one of the most direct routes for a QS to sit at the centre of contract administration.
What the Employer's Agent does
The Employer's Agent acts for the employer in almost every matter under the contract unless the employer states in writing that it wants to reserve certain functions to itself. In practice this covers assessing and certifying interim payment applications, reviewing progress against the programme, agreeing valuations of variations, issuing extension of time decisions, and administering practical completion and the defects period. According to RICS practice guidance, the Employer's Agent is also expected to advise the employer on its rights regarding matters such as liquidated damages, even though certain actions - giving possession of the site, making payment, and issuing notices that affect the employer's own financial position - legally remain the employer's own to take.
- Certifying interim payments and agreeing valuations of the works
- Assessing extension of time claims against the Relevant Events listed in the contract
- Reviewing design submissions against the Employer's Requirements for compliance
- Administering practical completion, the rectification period and final certificate
- Acting as the main point of contact between employer and contractor throughout
Payment Under the JCT Design and Build Contract
Payment under JCT DB follows the interim certification cycle common across the JCT suite, but with the Employer's Agent performing the certifying function instead of an architect or contract administrator. Understanding the timeline is essential, because missing a deadline under the JCT payment mechanism has real financial consequences for whichever party fails to act.
The interim payment cycle
The contractor submits an interim application for payment, typically monthly, valued against the Contract Sum Analysis and the value of variations instructed to date. The Employer's Agent (or the employer, depending on the payment route selected) must then issue a payment notice within the timescale set out in the contract, stating the sum considered due and the basis of that calculation. If the paying party wants to pay less than the amount applied for, it must issue a valid pay less notice by the deadline specified in the contract - miss that deadline, and the paying party is generally obliged to pay the full sum stated in the contractor's application, even where that figure is disputed or overstated. This 'notified sum' mechanism, inherited from the Housing Grants, Construction and Regeneration Act 1996 as amended, is one of the most commercially significant procedural traps on any JCT contract, DB included.
Retention and the final account
As with other JCT forms, a percentage of retention is typically withheld from each interim certificate, with half released at practical completion and the balance released after the rectification period and issue of the final certificate. The final account process on a design and build project draws heavily on the Contract Sum Analysis to value the agreed final position, including all instructed variations, loss and expense claims and any adjustments for extensions of time.
JCT Design and Build vs the Standard Building Contract
Choosing between JCT DB and the JCT Standard Building Contract (SBC) is one of the most common procurement decisions a QS advises on. The two forms allocate design risk, administration and cost certainty very differently, and the right choice depends heavily on how much design the employer wants to control before tender.
Table 02 / Route comparison
Design and Build vs Standard Building Contract
| Feature | JCT Design and Build | JCT SBC |
|---|---|---|
| Design responsibility | Contractor | Employer's consultants |
| Contract administrator | None - Employer's Agent | Architect / Contract Administrator |
| Cost certainty at tender | Higher | Lower until design finalised |
| Employer design control | Lower after novation | Retained throughout |
| Typical use case | Commercial, industrial, fit-out | Bespoke, high-spec, heritage projects |
Source: JCT contract guidance and RICS appropriate contract selection guidance note.
Neither route is inherently better - the decision should follow the employer's priorities. An employer that wants absolute design control and is prepared to manage the interfaces between multiple consultants will usually be better served by SBC. An employer that wants price and programme certainty from an early stage, and is comfortable ceding day-to-day design decisions to the contractor's team, will typically favour design and build.
Further Reading: here is a curated explainer of the NEC and JCT contracts.
What Changed in the JCT DB 2024 Edition
JCT released the 2024 edition of the Design and Build Contract as part of its wider refresh of the JCT suite, with changes described by legal commentators as evolutionary rather than revolutionary - the core structure and much of the 2016 drafting remains intact, but several updates matter directly to how QSs administer the contract day to day.
- Gender-neutral drafting throughout, replacing 'he shall' with 'it shall'
- Electronic notices are now expressly permitted for most contractual communications
- Collaborative working has moved from a supplemental provision into the main Articles
- Sustainability obligations now form part of the main conditions rather than a bolt-on schedule
- New Building Safety Act provisions identifying the Principal Designer and Principal Contractor, mirroring CDM 2015 duties
- Three new Relevant Events: asbestos/contaminated material/unexploded ordnance, epidemic, and exercise of a statutory power
- The period for the employer to decide an extension of time claim has been reduced from 12 weeks to 8 weeks
- Full fluctuations option wording has been removed from the printed contract and must be downloaded separately from the JCT website
For commercial teams, the shortened extension of time decision period is one of the most operationally significant changes - it compresses the time available to assess delay claims and means Employer's Agents need tighter internal processes for gathering programme evidence. The new Building Safety Act provisions are also critical for any higher-risk building project, since incorrect identification of duty holders can create compliance exposure under the Building Safety Act 2022 quite separately from the underlying construction contract.
Practical Tips for Administering a JCT DB Contract
Beyond understanding the mechanics, there are a handful of habits that consistently separate well-run JCT DB projects from ones that end up in dispute. These apply whether you're sitting as Employer's Agent, working within the contractor's commercial team, or advising either party pre-contract.
Before contract execution
- Cross-check the Employer's Requirements against the Contractor's Proposals line by line before signing - unresolved discrepancies are read in the contractor's favour.
- Confirm whether design liability is fitness for purpose or reasonable skill and care, and check this aligns with available professional indemnity cover.
- Agree the Contract Sum Analysis breakdown in enough detail to value variations fairly later in the project.
- Check which Relevant Events and Relevant Matters have been amended from the standard JCT drafting.
During the project
- Track every payment notice and pay less notice deadline - missing one has direct financial consequences.
- Keep a live register of design submissions and Employer's Agent comments to evidence compliance with the Employer's Requirements.
- Assess extension of time notices promptly given the shortened 8-week decision period in the 2024 edition.
- Document instructed changes formally rather than allowing informal site instructions to accumulate unrecorded.
Frequently Asked Questions
What is the JCT Design and Build Contract used for?
It is used where the employer wants a single contractor to take responsibility for both designing and constructing the works, in exchange for a lump sum price. It suits commercial, industrial, residential and fit-out projects where the employer prioritises price and programme certainty over retaining full design control.
Who carries design risk under JCT Design and Build?
The contractor generally carries responsibility for completing and coordinating the design and, unless the contract is amended, for its fitness for purpose. However, the contractor is not responsible for the adequacy of the Employer's Requirements themselves, which remains the employer's risk.
What is the difference between the Employer's Requirements and the Contractor's Proposals?
The Employer's Requirements set out the employer's brief, specification and performance criteria. The Contractor's Proposals are the contractor's response, including its design solution and the Contract Sum Analysis, and become the standard the contractor must build to once the contract is signed.
Who administers a JCT Design and Build contract if there is no architect?
The Employer's Agent, appointed by the employer, runs the contract day to day - certifying payment, assessing extensions of time and reviewing design compliance - although certain actions such as giving possession of the site and making payment remain the employer's own responsibility.
What happens if a pay less notice is not issued on time under JCT DB?
If the paying party fails to issue a valid pay less notice by the contractual deadline, it is generally required to pay the full sum stated in the contractor's payment application, even if that sum is considered overstated.
What changed in the JCT Design and Build Contract 2024 edition?
Key changes include gender-neutral drafting, permission for electronic notices, collaborative working and sustainability moved into the main conditions, new Building Safety Act dutyholder provisions, three new Relevant Events, and a reduction in the employer's extension of time decision period from 12 to 8 weeks.
Is JCT Design and Build better than the JCT Standard Building Contract?
Neither is universally better - it depends on the employer's priorities. Design and Build typically gives greater cost certainty and a single point of responsibility, while the Standard Building Contract gives the employer more direct control over design decisions throughout the project.
Final Thoughts
The JCT Design and Build Contract remains one of the most widely used procurement routes in UK construction because it answers a genuine commercial need: a single point of responsibility and greater price certainty in exchange for the employer ceding day-to-day design control. For quantity surveyors, the form rewards precision at exactly the moments it is easiest to rush - drafting or checking the Employer's Requirements, agreeing the Contract Sum Analysis, and tracking payment notice deadlines with discipline.
The 2024 edition's changes are incremental rather than transformative, but the shortened extension of time period and new Building Safety Act provisions mean commercial teams administering current projects need to build tighter internal processes than the 2016 edition demanded. Understanding where design risk genuinely sits - and where it doesn't - is the single most valuable piece of knowledge a QS can bring to a design and build project, whether advising an employer at procurement stage or running the contract as Employer's Agent through to final account.
