Turnkey Contracts UK: Design-Build & EPC Explained

What this document is

A turnkey contract is a construction agreement where one contractor takes full responsibility for delivering a finished, functional project to the client. The name comes from the idea that the client only needs to turn the key on completion to start using the building, plant, or facility.

In legal terms, it 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 is often delivered under standard forms such as the JCT Design and Build Contract or the FIDIC Silver Book for larger engineering schemes.

The client agrees a price and a completion date, and the contractor absorbs most of the risks that sit between those two points. This shifts a significant amount of design risk, coordination risk, and programme risk away from the employer, which is precisely why sophisticated clients use it, and precisely why contractors price it accordingly.

How to use this document

1. Define your employer's requirements clearly. The document that sets out what you want the contractor to deliver is the single most important piece of paper in a turnkey deal. Vague requirements produce vague outcomes. Set out performance criteria, quality standards, completion tests, and any non-negotiable design elements before you go to tender.
2. Choose the right standard form and tailor it. Most UK turnkey projects use a JCT Design and Build Contract, an NEC4 Engineering and Construction Contract under Option A or C, or a FIDIC form for international or heavy engineering work. Each allocates risk differently, and the schedule of amendments usually matters more than the base form itself.
3. Agree the price structure and payment mechanism. Turnkey deals are commonly fixed-price lump sum, but they can also run on a guaranteed maximum price or target cost basis. Make sure the payment schedule complies with the Housing Grants, Construction and Regeneration Act 1996, which governs interim payments and the right to refer disputes to adjudication.
4. Lock down design liability and warranties. Because the contractor is designing as well as building, you want a clear design warranty, ideally fitness for purpose rather than simply reasonable skill and care. Check the professional indemnity insurance position carefully, because some insurers exclude fitness for purpose obligations.
5. Plan the completion tests and handover process. A turnkey project is not complete when the building looks finished. It is complete when it passes the agreed performance tests. Define those tests, the pass criteria, the rectification process for snagging, and the documentation the contractor must hand over, including as-built drawings, operation and maintenance manuals, and statutory certificates.