Photo by RIBA.
For any home improvement project, drawing up a written contract with your chosen builder is highly advisable. Even for a simple extension, you are making a significant investment that deserves protection.
Contracts don’t have to be complicated; there are standard forms designed specifically for homeowners looking to renovate or extend their properties. These contracts are typically straightforward and user-friendly. Establishing a building contract can help ensure quality, manage timelines, and control costs, benefiting all parties involved.
Find out more in our guide below.
When you agree to work with a builder, whether formally or informally, a contract is formed. A building contract provides peace of mind and enhances your control over project management, ensuring the work is carried out according to the plans and completed on schedule and within budget. While it may not eliminate all risks, having a contract can help the building process proceed more smoothly.
The primary advantage of a building contract is the clarity it provides, outlining:
Rear extension by Pensaer, under construction.
Be cautious if a builder is reluctant to use a building contract; this could suggest unprofessionalism or, worse, bad faith.
A written contract safeguards both their interests and yours by clearly outlining the work to be completed for the agreed price. There’s no justification for not having one in place. Building work represents a significant investment – would you purchase a car or any other major item without an agreement first? The same principle applies to building work.
In most cases, no, you don’t need to seek legal advice.
If you’ve appointed an architect, they can guide you on the most suitable form of contract and handle all arrangements on your behalf. It’s advisable to use an industry-standard building contract whenever possible – such as those published by the Royal Institute of British Architects (RIBA) or The Joint Contracts Tribunal (JCT) – as these have been rigorously tested by the UK legal system.
Legal advice is typically only necessary if you are entering into a bespoke agreement, which is generally best avoided due to the lack of the same thorough testing that standard contracts undergo.
The contents of a building contract can vary based on its type, but most include provisions for the following key elements:
Ground floor rear extension by EBBA Architects. Build cost £281,00 over 170 square metres Gross Internal Floor Area (GIFA). Photo by Nick Dearden.
For straightforward home improvement projects, the two most commonly used building contracts are:
Both contracts are straightforward agreements written in plain English. The JCT HO/O has two versions: one with a consultant and one without, while the RIBA DBC is a single version that can be administered by you or a consultant. The JCT HO/O is best for simpler projects, but if you plan to appoint specific companies for tasks like a low energy heating system or specialist glazing, the RIBA DBC is preferable as it accommodates their involvement. The JCT HO/O does not offer this flexibility.
Also, the JCT HO/O does not allow for phased start and completion dates, which is crucial if you are living on-site during the renovation and wish to occupy completed areas. Additionally, it does not cover liquidated damages.
For larger and more complex home improvement projects, consider more comprehensive agreements such as:
The JCT MW is suitable for contracts valued up to £500K, while the JCT IC is appropriate for projects valued up to £1m. An architect can provide guidance on which building contract is most applicable to your specific project.
JCT MW is suitable for many home extension projects such as this terrace house renovation and rear extension by Tuckey Design Studio. Build cost £115,000 over 150 square metres GIFA. Photo by James Brittain.
If the contractor delays the completion date, liquidated damages allow you to claim compensation for any losses incurred, such as the need for temporary accommodation if you cannot move in as planned. Including a liquidated damages clause helps prevent disputes over compensation and enables both parties to manage risks proactively. While the RIBA DBC, JCT MW, and JCT IC contracts include provisions for liquidated damages, the JCT HO/O does not.
The status of subcontractors – companies appointed by you or the builder – can significantly affect the project’s timeline and costs. When you hire a builder for your renovation, they act as the main contractor, responsible for managing the project on-site. They may engage domestic subcontractors for specific tasks, like plumbing or electrical work, which remain the main contractor’s responsibility.
If you wish to appoint a specific company for a particular job, such as a specialist heating system, they are considered a nominated subcontractor and will be your responsibility. Alternatively, you can use a named subcontractor approach, where you provide a list of companies for the main contractor to choose from; in this case, they remain the main contractor's responsibility.
To minimise the risk of delays, disputes, and cost increases, it is generally advisable to avoid using nominated subcontractors.
A digital copy of the RIBA Domestic Building Contract costs £45 plus VAT, while a hard copy is priced at £35 plus VAT. For the JCT Building Contract for a Home Owner/Occupier without a consultant, both digital and hard copies are £35 plus VAT. If a consultant is overseeing the work, the cost increases to £34 plus VAT.
The JCT Minor Works Building Contract is £88 plus VAT for a digital copy and £44 plus VAT for a hard copy. Lastly, the JCT Intermediate Building Contract costs £78 plus VAT for a hard copy and £156 plus VAT for a digital version.
Complex residential projects, such as this ground and basement extension by Proctor & Shaw Architects, require a more comprehensive building contract, such as JCT IC. Photo by Ståle Eriksen.
In addition to drafting the contract, an architect will prepare detailed technical plans and specifications that outline how the project should be constructed. These documents are crucial for controlling both build quality and costs; generally, the more detail you provide, the better.
When contract documents lack detail, builders may end up guessing your intentions or constructing based on their preferences. This can lead to quality issues and increased costs. Moreover, having a comprehensive set of contract documents minimises the risk of disputes with your builder. When everything is clearly defined from the outset, there’s little room for disagreement.
Hiring an architect as your contract administrator will help ensure the site phase runs smoothly. Initially, they will recommend the most suitable building contract for your project and prepare the necessary drawings and specifications that define the scope of the agreement.
Once construction begins, the architect will carry out regular site inspections to ensure the work aligns with the plans. They will address any defects, respond to site queries, monitor costs, and certify payments to the builders. Their involvement in the design process positions them well to liaise effectively with the builder regarding contract documents and site quality.
As the project nears completion, the architect will facilitate final certifications and payments, as well as manage the defects period outlined in the contract.
READ: How Much Do Architects Cost?
Architects have extensive experience in managing the building process to ensure everything runs smoothly. If you hire a builder without an architect, use a contract like the RIBA Domestic Building Contract, which allows you to act as the contract administrator.
For larger projects, it's wise to appoint a professional, such as an architect, to oversee the contract and works. Investing in expert services reduces risks and ensures a smoother, more successful build.
The information provided in this article is intended for general guidance and educational purposes only. For specific expert advice on your project, consult a skilled residential architect featured on Designs in Detail.
About the Author
Aron Coates is an architect with over two decades of experience, working on projects ranging from historic building restoration to contemporary home design.
