Turnkey Contracts UK: Design-Build & EPC Explained

At a glance

• What it is: a construction agreement where one contractor takes single-point responsibility for design, procurement, construction and handover of a finished, working building or facility.
• Common labels: "turnkey", "design-build" (the usual UK building-sector term), and "EPC" — engineering, procurement and construction (the usual term for heavy engineering, energy and industrial schemes).
• Standard forms: in the UK, turnkey projects are typically delivered under a JCT Design and Build Contract, an NEC4 Engineering and Construction Contract, or a FIDIC form (commonly the FIDIC Silver Book) for international or heavy engineering work.
• Statutory payment and adjudication rights: the Housing Grants, Construction and Regeneration Act 1996 (as amended) applies to almost all UK construction contracts, including turnkey ones. It guarantees a right to adjudicate a dispute at any time and requires a compliant interim payment mechanism.
• The narrow exception: a contract with a "residential occupier" — broadly, work on a home one of the parties occupies or intends to occupy — falls outside the Act's payment and adjudication rules. Courts interpret this exception strictly.
• If the contract is silent or non-compliant: the Scheme for Construction Contracts (England and Wales) Regulations 1998 automatically fills the gaps in the payment and adjudication terms.
• Taller or higher-risk buildings: the Building Safety Act 2022 adds statutory dutyholder roles and mandatory "gateway" approval points for buildings that are at least 18 metres tall or have at least 7 storeys and contain residential units — always check the current GOV.UK criteria for a given project.

What is a turnkey contract?

A turnkey contract is a construction agreement under which one contractor takes full responsibility for delivering a finished, functional project to the client. The name reflects the idea that the client only needs to turn the key on completion to start using the building, plant, or facility — everything up to that point is the contractor's problem to solve.

In legal terms, this is a single-point-of-responsibility arrangement. The contractor designs the works, procures the materials and plant, manages the subcontractors, carries out the construction, and hands over a tested and operational asset. In the UK, turnkey projects are commonly delivered under standard forms such as the JCT Design and Build Contract for building work, or the FIDIC Silver Book for larger international or engineering schemes; some parties instead use an NEC4 Engineering and Construction Contract with an appropriate option, adapted to place design responsibility on the contractor.

The client agrees a price and a completion date, and the contractor absorbs most of the risk that sits between those two points. This shifts design risk, coordination risk, and programme risk away from the client — which is exactly why sophisticated clients choose the structure, and exactly why contractors price it accordingly.

How UK law treats turnkey contracts

A turnkey contract is still, legally, a "construction contract", and construction contracts in the UK are governed by a specific statutory framework regardless of what label the parties give the deal.

The Housing Grants, Construction and Regeneration Act 1996

The Housing Grants, Construction and Regeneration Act 1996 — often called "the Construction Act" — sets out mandatory rules for construction contracts in Part II of the Act. It was substantially amended by the Local Democracy, Economic Development and Construction Act 2009, whose construction-contract provisions came into force in England and Wales on 1 October 2011. Those amendments removed the previous requirement for a contract to be in writing before the Act's adjudication and payment rules applied, added a requirement that adjudicators be able to correct clerical errors, and restricted contract terms that tried to make the referring party pay the adjudicator's costs regardless of outcome.

Two rights under the Act matter most for a turnkey project:

• The right to adjudicate at any time. Under section 108, every party to a construction contract has the right to refer a dispute to adjudication at any time, and the parties cannot contract this right away.
• A compliant payment mechanism. The Act requires the contract to set out how and when interim payments are calculated and paid, and to provide for payment notices and, where the payer intends to pay less than notified, a pay less notice — see below.

There is one important, narrowly drawn exception. Under section 106, the Act's payment and adjudication provisions do not apply to a construction contract with a residential occupier — one that principally relates to work on a dwelling that a party to the contract occupies, or intends to occupy, as their residence. Courts have interpreted this exception strictly, and there is no reported case where a party successfully relied on it to avoid adjudication. Most commercial and larger self-build turnkey contracts will not benefit from it.

The Scheme for Construction Contracts

If a construction contract does not include payment or adjudication terms that comply with the Act, the missing terms are not left blank — they are supplied automatically by the Scheme for Construction Contracts (England and Wales) Regulations 1998. This means a poorly drafted turnkey contract does not escape the statutory scheme; it simply has the Scheme's default terms read into it in place of the missing or non-compliant provisions.

Payment notices and pay less notices

Under sections 110A and 111 of the Act, the payer (or another person the contract specifies) must give a payment notice stating the sum it considers due for a given payment period, no later than the deadline set by the contract. If the payer wants to pay less than that notified sum, it must separately serve a pay less notice setting out the lower amount and the basis for it, before the final date for payment.

If neither notice is given in time, section 111 requires the payer to pay the sum applied for in full — a situation commonly referred to as a "smash and grab" adjudication. Because turnkey payments are typically large, staged lump sums tied to design and construction milestones, a missed notice deadline can be an expensive and entirely avoidable mistake for either party.

The right to suspend for non-payment

If a sum properly due under section 111 is not paid by the final date for payment, section 112 gives the unpaid party the right to suspend performance of some or all of its obligations under the contract. At least 7 days' written notice of the intended suspension, and the grounds for it, must be given first. Time lost through a valid suspension is added back when calculating the completion date, so a contractor exercising this right properly should not also face a delay claim for the same period.

Standard forms used for turnkey projects

The "turnkey" label describes the commercial structure, not a single legal document. In practice, UK turnkey projects are delivered under one of a small number of standard forms, each allocating risk differently:

• JCT Design and Build Contract — the most common choice for UK building projects where the contractor takes on both design and construction. The employer sets out its requirements, the contractor responds with proposals, and the contract price reflects the contractor's own design.
• FIDIC Silver Book (EPC/Turnkey Contract) — widely used for international and heavy engineering, energy, and industrial projects, where the contractor carries close to full responsibility for design, permits and completion, in exchange for a higher price to reflect that risk transfer.
• NEC4 Engineering and Construction Contract — not turnkey-specific, but frequently adapted (typically Options A or C, with Contractor design added) to build a single-point-responsibility structure with NEC's collaborative administration mechanics.

Whichever base form is chosen, the schedule of amendments the parties negotiate on top of it usually matters more to the final risk allocation than the base form's standard wording.

Design risk and single-point responsibility

Because the turnkey contractor is responsible for both design and construction, the precise wording used to describe its design obligation matters enormously.

Fitness for purpose vs reasonable skill and care

A fitness for purpose obligation is a stricter, effectively no-fault standard: the finished works must be fit for their intended purpose, regardless of whether the contractor's design team was at fault. A reasonable skill and care obligation — the standard most professional consultants owe at common law and under their professional indemnity insurance — only requires the contractor's designers to have exercised the skill and care of a reasonably competent practitioner, even if the result later proves unsuitable.

This distinction is not academic. Many professional indemnity insurance policies held by architects, engineers and specialist subcontractors exclude cover for fitness-for-purpose obligations, because the insured could be liable even without any negligence. A turnkey contract that imposes fitness for purpose on the head contractor, without checking whether that risk can be passed down and insured through the supply chain, can leave the contractor carrying an uninsurable liability.

Employer's requirements and contractor's proposals

The document setting out what the client wants delivered — usually called the employer's requirements — is one of the most important documents in a turnkey deal, because it defines the baseline the contractor is pricing against and designing to. The contractor responds with its contractor's proposals, and the two documents together, read alongside the contract's design-liability clause, determine who is responsible when something does not turn out as expected. Vague or incomplete employer's requirements tend to produce vague outcomes and increase the risk of a dispute over whether a problem originated in the client's brief or the contractor's design response.

The Building Safety Act 2022 and higher-risk buildings

For certain taller or higher-occupancy residential buildings, UK construction law now layers additional statutory obligations on top of the Construction Act framework described above. The Building Safety Act 2022 created a new regime for "higher-risk buildings", overseen by the Building Safety Regulator, which has acted as the building control authority for higher-risk building work since October 2023.

GOV.UK's guidance sets out the criteria for determining whether a new building being designed and constructed is a higher-risk building: broadly, a building at least 18 metres in height or with at least 7 storeys, containing at least two residential units, and not falling within a small number of excluded categories (such as hotels or barracks). The criteria and thresholds are specific and subject to further regulation, so check the current position on GOV.UK for any given project rather than relying on a rule of thumb.

Where a turnkey project falls within scope, the contract needs to allocate the Act's statutory dutyholder roles clearly — including principal designer and principal contractor duties — alongside the usual design-and-build risk allocation, and needs to build in the mandatory "gateway" approval points and the "golden thread" of building safety information that must be created, maintained and handed over at completion. These are statutory duties that sit on top of, not instead of, the contractual design obligations discussed above.

Contractor insolvency and how clients protect against it

Committing the whole project to one contractor is precisely what makes turnkey structures efficient — and precisely what makes contractor insolvency one of the most serious risks a client faces. If the turnkey contractor becomes insolvent partway through, the client can be left with an unfinished building, an unresolved design, and a difficult path to completing the works through someone else.

Typical protections, which should be negotiated before signing rather than after problems emerge, include:

• Performance bonds, usually issued by a bank or surety, that pay out if the contractor fails to complete.
• Parent company guarantees, where the contractor sits within a corporate group with a stronger balance sheet.
• Collateral warranties from key subcontractors, consultants and designers, giving the client (and often future owners, tenants or funders) a direct contractual right against those parties even though the client's main contract is only with the head contractor. See our guide on collateral warranties and third party rights for how these work.
• Retention monies, withholding a percentage of each payment until defects are made good.

What to check before signing a turnkey contract

1. Define the employer's requirements clearly. Set out performance criteria, quality standards, completion tests and any non-negotiable design elements before going to tender. Vague requirements produce vague, disputable outcomes.
2. Choose the right standard form and check the amendments. A JCT Design and Build Contract, an NEC4 Engineering and Construction Contract, or a FIDIC form each allocate risk differently — and the schedule of amendments usually matters more than the base form.
3. Confirm the payment mechanism complies with the Construction Act. Check the contract sets out payment notices and pay less notices consistent with sections 110A and 111 of the Housing Grants, Construction and Regeneration Act 1996, so neither side is caught out by a missed deadline or forced back onto the Scheme for Construction Contracts by default.
4. Lock down design liability. Decide whether the contractor's design obligation is fitness for purpose or reasonable skill and care, and check whether that liability is actually insurable through the professional indemnity cover held by the contractor and its design team.
5. Check whether the Building Safety Act 2022 applies. If the project could be a higher-risk building, confirm the current GOV.UK criteria and make sure the contract allocates the statutory dutyholder roles and gateway process, not just the usual design-and-build risk.
6. Plan for contractor insolvency. Negotiate performance bonds, parent company guarantees, collateral warranties and retention before signing — not after a problem arises.
7. Agree the completion tests and handover process up front. A turnkey project is complete when it passes the agreed performance tests, not simply when the building looks finished. Define those tests, the pass criteria, the snagging and rectification process, and the documentation the contractor must hand over, including as-built drawings, operation and maintenance manuals, and statutory certificates.

This guide provides general information about how turnkey construction contracts work under the law of England and Wales. It is not legal advice and is not a substitute for advice tailored to your specific project. The law described was accurate as at July 2026 and is subject to change — always check GOV.UK and legislation.gov.uk for the most current position, particularly the Building Safety Act 2022 criteria, which are kept under ongoing review.

Last reviewed: July 2026 by a non-practising solicitor · Next review due: July 2027 or on legislative change.