JCT Contracts for London Home Extensions: What They Are and Why You Need One

The JCT Minor Works Building Contract 2016 (MW 2016) is a short-form standard contract suitable for residential extension projects where the works are straightforward (one trade or a small number of trades), a Contract Administrator (architect or project manager) is appointed to act between the client and contractor, and the contractor is responsible for building but not for design. Key provisions of MW 2016: Contract Documents: The contract sum, the contract documents (scope of works, drawings, specification), the programme, and the start and completion dates are agreed upfront. Variations: The Contract Administrator issues Variation Instructions in writing for any changes to the agreed scope — the contractor prices each variation before (or shortly after) instructing the work. Disputed variation costs can be referred to adjudication. Payment: The contractor is entitled to interim payment at intervals specified in the contract (typically monthly). The Contract Administrator certifies the value of work done, and the employer pays within the contractual payment period. A Pay Less Notice must be given before the payment deadline if the employer disputes the certified amount — failure to pay on time entitles the contractor to suspend work. Practical Completion and Retention: The Contract Administrator certifies practical completion when the works are substantially complete. Half the retention (typically 2.5% of the contract sum) is released at this point; the remaining half is released at the end of the Defects Liability Period (typically 6 or 12 months). Defects: The contractor is obliged to make good any defects that appear during the Defects Liability Period, at no cost to the employer. Insurance: MW 2016 requires the contractor to hold Employer's Liability insurance and public liability insurance, and requires the works to be insured (either by the contractor for new works, or by the employer for works to an existing structure). Termination: Either party can terminate the contract in defined circumstances — the contractor for non-payment, the employer for contractor default. Adjudication: MW 2016 incorporates the statutory right to adjudication — either party can refer a dispute to an adjudicator at any time, with a 28-day decision period.

The JCT Homeowner/Occupier Contract (HO/C) is a simpler form designed specifically for works to an owner-occupied home where there is no architect or contract administrator acting between the client and the contractor. It is appropriate for smaller projects (typically up to £50,000) such as kitchen refurbishments, bathroom renovations, smaller extensions, and decorating and maintenance works. Key differences from MW 2016: No Contract Administrator: Under HO/C, the homeowner deals directly with the contractor — there is no third party certifying payment or issuing instructions. This places more management responsibility on the homeowner. Simpler payment mechanism: The contract provides for stage payments (milestone-based) or interval payments, without the formal interim certificate mechanism of MW 2016. Retention: HO/C includes a retention provision. Defects period: Typically 3 or 6 months after practical completion. Disputes: HO/C includes a shorter dispute resolution process appropriate for the scale of works. The HO/C contract is available directly from the JCT website or from legal stationers. It comes with a Guide to the JCT Homeowner Contract that explains each clause in plain language.

Whether using a standard JCT form or a bespoke contractor contract, the following elements should be present in any building contract for a London extension project: Identification of the parties: Full legal names and addresses of both the homeowner (employer) and the contractor. Description of the works: Reference to the contract documents (scope of works, drawings, specification) that fully describe what the contractor is to build. The contract sum: The agreed price for the described works, exclusive of VAT. Programme and dates: The contractual start date and the date for practical completion — with any applicable damages for late completion (liquidated damages). Payment provisions: The basis for interim payments (monthly, stage, or milestone), the notice period for payment applications and payment certificates, and the payment period from certificate to payment. Variation procedure: How changes to the scope are to be instructed and priced. Insurance requirements: The minimum levels of employer's liability and public liability insurance the contractor must hold throughout the works, and the agreed position on insurance of the works. Defects provisions: The duration of the defects liability period and the process for notifying and making good defects. Dispute resolution: The agreed dispute resolution mechanism (typically adjudication for JCT contracts). Practical completion: A definition of what constitutes practical completion for the purposes of triggering retention release and the start of the defects period.

A significant number of London residential extension projects proceed on the basis of little more than an accepted quote and a handshake. The reasons are often: the contractor does not offer a formal contract and the homeowner does not know to ask for one; the homeowner feels that asking for a formal contract will insult the contractor or imply distrust; the homeowner believes the quote itself is sufficient; or the project is perceived as too small to need a formal contract. The practical consequences of not having a written contract: Scope disputes — without a clear contractual description of what is included, arguments arise over whether items such as external paving, snagging, or connection to existing systems are within the contractor's obligation. Without written records, these disputes are very hard to resolve. Payment disputes — the contractor may claim that the homeowner owes additional sums that the homeowner disputes; or the homeowner may withhold payment for defects without a proper contractual mechanism, exposing themselves to claims for non-payment. Defects liability — without a contractual defects period, the contractor's obligation to return and fix defects at no charge is governed by common law implied terms, which are harder to enforce in practice than a clear contractual provision. Programme disputes — without a contractual completion date, the homeowner has no legal remedy if the contractor takes significantly longer than expected. The time invested in preparing a proper contract before starting a project is a small fraction of the value it provides in protecting both parties if the project does not go smoothly.