20.03.2024

Design and build contracts are commonly used in the construction industry in the UK. This guide provides an overview of design and build contracts, their advantages, the roles of the contractor and architect, a comparison with traditional contracts, and the different types of design and build contracts available. This is especially important for anyone considering a home extension in the UK, so let’s take a look.

What is a Design and Build Contract?

This is when the contractor is responsible for both the design and construction of a project. Instead of separate contracts for design and construction that include multiple parties like architects and builders, the client enters into a single agreement with the contractor – that is, the design and build company – streamlining the process.

Advantages of a Design and Build Contract

  • Single point of responsibility: With a design and build contract, the contractor assumes full responsibility for the entire project, including design, construction, and coordination. This reduces the client’s administrative burden and ensures clear accountability.
  • Faster project delivery: Since design and construction are integrated, there is no need for time-consuming bid processes between the architect and contractors. This can lead to faster project delivery and reduced construction time.
  • Control of costs and reduced project costs: Design and build contracts often provide cost certainty to clients since the contractor is responsible for managing and controlling the project’s budget. This can help avoid cost overruns and change orders, as well as make your project more affordable.
  • Better collaboration: Design and build contracts utilise a team that has always worked together rather than people who are strangers from different organisations that have their own separate goals and values. This means they already work well as a team, which creates effective communication, problem-solving, and innovation.

Role of the Contractor in a Design and Build Contract

Here, the contractor takes on a more prominent role compared to traditional contracts. Their responsibilities include:

  • Design development: The contractor works closely with the client to develop the project’s design, ensuring it meets the client’s requirements and adheres to relevant regulations and standards.
  • Construction: The contractor is responsible for executing the construction phase, managing subcontractors, procuring materials, and ensuring the project is completed within the agreed-upon timeframe and budget.
  • Project management: The contractor oversees the entire project, including scheduling, budgeting, quality control, and coordination of various stakeholders.

Architect’s Role in a Design and Build Contract

For most residential extensions, you don’t need an architect if you work with a design and build company, which is one of the biggest cost-saving benefits. However, there will be an experienced specialist who takes on this role. The design specialist or architect in a design and build company has more of a team role in the project when it’s a design and build contract, working directly with the contractor and client to develop the building or extension’s design. Their responsibilities typically include:

  • Developing the initial design concept: The design specialist or architect collaborates with the client to establish the project’s design objectives, vision, and requirements. They develop an initial concept, which the contractor refines during the design development phase.
  • Technical support: They will also provide technical expertise and guidance to the contractor during the design phase, ensuring compliance with building codes, rules for extensions, regulations, and industry standards.
  • Construction administration: During the building process, they assist the contractor in overseeing the construction phase, reviewing shop drawings, conducting site inspections, and addressing any design-related issues that may arise.

Traditional Building Contracts vs. Design and Build Contracts

Traditional contracts involve separate agreements with architects and all the different contractors, where the architect’s design is completed and signed off on by the client before the contractor is engaged. The architect here is completely separated from the construction process – if you finish with their services and then need changes made to your design, you will have to go and renegotiate with them. 

In contrast, design and build contracts are all-in-one services. They integrate both design and construction under a single contract, where the architect or design specialist and the contractor, as well as any other specialists, work as a single team. This means that they are involved in the process from concept and design through construction until the project is completed.

Key differences include:

  • Responsibility: In a traditional contract, the client assumes greater responsibility for coordinating between the architect and contractor. Design and build contracts transfer this responsibility to the contractor.
  • Collaboration: Design and build contracts promote collaboration with and early involvement of the contractor as well as other professionals on the team. Because all the relevant parties, including the client, are involved, it’s easier to work together or make changes throughout the process. Traditional contracts involve sequential processes where each process is signed off before the next can occur. This can hinder collaboration because parties work independently. For example, if the architect’s plans are signed off but the client decides they actually want a larger or another window, the process has to essentially start over. 
  • Risk allocation: Traditional contracts often allocate more risk to the client, while design and build contracts transfer some risk to the contractor, who is responsible for both design and construction.

Types of Design and Build Contracts in the UK

  • Novation design and build contract: Here, the client enters into a contract with the architect initially. Once the design is sufficiently developed, the architect’s contract is novated (transferred) to the contractor, who takes on responsibility for the design and construction.
  • Two-stage design and build contract: In the first stage, the client engages a contractor based on preliminary information. The contractor will work with the client and architect to develop the design further. Once the design is sufficiently developed, the contract is finalised, and construction commences.
  • Negotiated design and build contract: This is a contract type that’s recommended when the client or contractor wants specific or non-traditional terms and responsibilities. The client and contractor will then negotiate the terms of the contract, including design and construction. This type of contract offers flexibility and allows for more direct involvement of the client in the decision-making process.
  • Turnkey design and build contract: In this contract, the contractor takes full responsibility for the design, construction, and delivery of a fully operational project. The client typically has minimal involvement in the design process and receives the completed project at the end. This is typically used in residential housing projects rather than an individual’s home.
  • Management contract: This can be included as part of a design and build contract. Here, the client appoints a design and build contractor as a manager to oversee and coordinate the project. The contractor manages the design and construction process, procuring and coordinating subcontractors and suppliers on behalf of the client.
  • Design, build, and operate (DBO) contract: This type of contract is typically used for infrastructure projects rather than private home builds and extensions. It extends beyond design and construction to include the operation and maintenance of the completed project. The contractor is responsible for delivering a fully functional facility and managing its operation for a specified period.
  • Public-private partnership (PPP) contract: PPP contracts involve collaboration between a public entity and a private contractor. The contractor assumes responsibility for the design, construction, financing, and operation of a public infrastructure project, such as roads or hospitals.
  • Framework design and build contract: This type of contract is established between the client and the contractor to facilitate the delivery of multiple projects over a specified period. It’s typically used for large-scale development, such as building several schools in an area. The contractor is engaged on a long-term basis and provides design and construction services for individual projects as they arise.

It’s important to note that specific terms and conditions can vary within each type of design and build contract, so they need to be read carefully regardless. At Plus Rooms, London’s leading design and build company, we typically use a negotiated design and build contract that can include project management if needed, as this gives our clients the most flexibility and works well within our team’s capabilities, leading to the best possible results.

Read more about building regulations in the UK.

Work with London’s Leading Design and Build Company for Your Dream Home

Plus Rooms is a full-service provider for all types of home extensions in the greater London area, including loft, kitchen, and kitchen diner extensions. As a top design and build company, we’ll work with you through the entire process, from designing your extension and managing planning permission to building the project and ensuring it is completed to your satisfaction. Please visit our website to see more of our home extensions, to be inspired by our kitchen extension design ideasto see reviews from past clients, and to start the journey towards your dream home.