Design-Build Contract

A design-build contract integrates design and construction responsibilities under a single contract awarded to one supplier (or consortium). Rather than procuring design separately, the contracting authority issues an employer's requirements document specifying functional outcomes, spatial requirements, and performance standards. The design-build contractor then develops the design and builds to it, carrying liability for both.

What is a Design-Build Contract?

Design-build procurement is common across European public contracting authorities for schools, hospitals, transport infrastructure, and utility works. Its appeal lies in the single-point-of-responsibility model: the authority manages one contract rather than coordinating a separate designer and a main contractor who might otherwise blame each other for interface problems.

Key characteristics:

• The authority writes an employer's requirements (performance specification), not a full technical design
• The winning contractor develops the design as part of delivery
• Design liability rests with the contractor's design team
• A single lump-sum or target-cost price covers both design and construction
• The contractor can optimise buildability during the design stage

Design-build differs from traditional procurement (design-bid-build) in a fundamental way: in design-bid-build, the authority's designer produces a complete design, contractors price against it, and the authority retains design liability. In design-build, the authority transfers design liability to the contractor.

Under Directive 2014/24/EU, design-build works contracts are subject to normal open competition requirements above the relevant thresholds. For very complex or innovative projects where the authority cannot fully specify requirements at the outset, the competitive dialogue procedure or competitive procedure with negotiation may be used to develop the requirement iteratively with shortlisted bidders before final tenders are sought.

In the UK, design-build (often called D&B) became the dominant model for public sector construction procurement through government frameworks and the Private Finance Initiative. Post-PFI, UK contracting authorities have continued to use D&B under standard JCT or NEC design-build contracts procured through frameworks on Construction Line or Crown Commercial Service vehicles.

Why it matters for bidders

Design-build bidding requires significant pre-tender investment. You must develop a concept design, engage specialist subcontractors and suppliers, and price a complex scope before knowing whether you will win. Bid costs for major design-build contracts can reach hundreds of thousands of euros or pounds.

However, the commercial upside is correspondingly significant. You control the design, which means you can engineer cost-effective solutions that your competitors may not have thought of. Your innovation and buildability thinking can differentiate your proposal at evaluation.

Example

A Scottish local authority procures a new secondary school under a design-build contract. The employer's requirements specify pupil capacity, curriculum requirements, accessibility standards, and sustainability targets. Three shortlisted contractors submit design proposals with fixed prices. The winning contractor develops the design to planning approval stage, constructs the building, and hands over a complete facility within the contract period.

Frequently Asked Questions

Who holds professional indemnity insurance in a design-build contract?

The design-build contractor is responsible for ensuring that the design elements are covered by professional indemnity (PI) insurance, either through their in-house design team or through subcontract designers who carry their own PI policies. The authority should verify PI coverage levels at tender stage, particularly for specialist technical elements.

Can a design-build contract use a target cost mechanism?

Yes. Some design-build contracts use a target cost or pain/gain mechanism rather than a pure lump sum, particularly where the scope retains uncertainty at tender stage. The contractor and authority share cost savings below the target and cost overruns above it according to an agreed share ratio. This blends design-build integration with the incentive alignment of performance-based contracting.

What is the difference between design-build and a turnkey contract?

A turnkey contract typically extends design-build to include full commissioning, testing, and handover of an operational facility. Design-build may stop at practical completion of the physical works, with the authority responsible for fitting out, equipping, and commissioning. In practice, the terms are often used interchangeably.