Building Contracts for London Home Projects: Which Type and What to Insist On

Many homeowners start work on a handshake, relying on a quote letter or email exchange as the basis for their arrangement with the contractor. This approach leaves significant commercial risk on both sides. Without a written contract: there is no agreed mechanism for dealing with variations (changes to scope) — the contractor can charge any amount for extras, or refuse to do necessary work; there is no agreed payment schedule — the contractor can demand large sums at short notice, or the homeowner can withhold payment without justification; there is no agreed programme — the contractor can demobilise and return weeks later without the homeowner having any contractual basis to enforce a timeline; and there is no agreed process for defects — after completion, disputes about what the contractor is responsible to fix, and for how long, become difficult to resolve. In England and Wales, domestic building contracts are subject to the same contract law as commercial contracts, but the protections of the Housing Grants, Construction and Regeneration Act 1996 (the Construction Act — which provides the right to stage payments and adjudication) do not automatically apply to residential occupier contracts. This means that if a homeowner living in the property being worked on has no written contract, they have fewer legal protections than a commercial client. The solution is straightforward: use a standard form contract, read it, and insist on a signed copy before work starts.

The Joint Contracts Tribunal (JCT) produces a suite of standard building contracts used throughout the UK construction industry. For domestic projects where the homeowner is living in the property being worked on, the JCT Homeowner Contract is specifically designed. It is published in two versions: the Building Contract for a Home Owner / Occupier (where no consultant is appointed — the homeowner and contractor manage the contract directly) and the Building Contract for a Home Owner / Occupier with Consultant (where an architect or consultant acts as contract administrator). The JCT Homeowner Contract is written in plain English, unlike some other JCT forms. It covers: the scope of the works (by reference to attached drawings and specification); the contract sum; the start date and expected duration; the payment structure (interim payments tied to progress, with retention); the process for instructing variations; the defects liability period (typically 12 months after practical completion); termination rights; and dispute resolution by adjudication. The JCT Homeowner Contract is available to purchase directly from the JCT website (ricsbooks.com) for approximately £30-£40. It is the most balanced and commonly understood standard form for domestic projects in London and is familiar to most experienced residential contractors. For projects above approximately £150,000, the JCT Minor Works Building Contract (2016 edition) provides a slightly more detailed framework and is more appropriate where a contract administrator (architect or surveyor) is appointed.

Payment is the most common source of dispute in domestic construction projects. A well-structured contract sets out payment obligations clearly, protecting both the homeowner (from being asked for money before work is done) and the contractor (from not being paid for completed work). Stage payments: the contract sum should be divided into payments linked to defined stages of work, not arbitrary dates or contractor requests. Typical stages for a London rear extension: mobilisation payment on start (10-15% of contract sum); foundations complete; ground floor slab complete; external walls to first floor or roof plate level; roof structure and watertight; first-fix mechanical and electrical; plastering complete; second fix complete and practical completion. The homeowner should be able to verify each stage milestone before releasing the payment. Retention: a retention — typically 3-5% of the contract sum — is withheld from each payment and released in two halves: 50% at practical completion and 50% at the end of the defects liability period (typically 6-12 months after practical completion). Retention protects the homeowner by ensuring the contractor has a financial incentive to return and fix defects after practical completion. Deposits: it is reasonable to pay a modest mobilisation deposit (10-15% of contract sum) before work starts to cover the contractor's initial material and mobilisation costs. A deposit demand of 25-50% or more is a commercial risk — if the contractor fails to perform or becomes insolvent after a large deposit is paid, recovery is difficult. Be cautious of any contractor who insists on a large upfront payment before materials are delivered to site.

Variations (changes to the agreed scope of work) are inevitable in most building projects. Materials are discontinued, site conditions differ from what was expected, the homeowner decides they want an additional element, or the design needs to be modified to comply with Building Control comments. A good contract should establish a clear procedure for variations: the homeowner or architect issues a written instruction describing the change; the contractor provides a written quotation for the additional cost (or saving) and any programme impact; the homeowner approves the variation in writing before the contractor proceeds; and the variation is added to (or deducted from) the contract sum formally. The most common failure in domestic contracts is that variations are instructed verbally, costs are not agreed before the work is done, and disagreements arise at the final account stage about what was agreed and how much it costs. The variation procedure only works if it is followed consistently. On a project where the homeowner changes their mind frequently or where the design is not well-developed before work starts, the number of variations can become significant — and the total cost of variations can easily add 10-25% to the original contract sum. Reducing variation cost requires good design development before construction starts, and discipline in following the written variation procedure for every change, however small.

Practical completion is the point at which the works are substantially complete and the homeowner can take occupation — even if minor snagging items remain outstanding. At practical completion: the homeowner takes possession of the works; 50% of the retention is released to the contractor; the risk for the works transfers from contractor to homeowner (the homeowner's buildings insurance becomes applicable); the defects liability period begins; and the contractor issues an application for the practical completion payment. The defects liability period (also called the rectification period) is typically six to twelve months after practical completion. During this period, the contractor is obliged to return to remedy any defects in materials or workmanship that become apparent. At the end of the defects liability period, a schedule of any remaining defects is issued to the contractor, who rectifies them, and the final 50% of retention is released along with any outstanding balance on the final account. The defects liability period is an important contractual protection for the homeowner — it provides a period during which the contractor remains financially invested in the quality of the work (because retention has not been fully released) and legally obligated to fix any defects that emerge. Snagging items identified at practical completion that are beyond minor finishing should be addressed before the practical completion certificate is issued, not left to the defects liability period.

Despite best intentions, disputes arise in construction projects. Common disputes in domestic projects include: disagreements about whether a variation was instructed and at what cost; whether work has been completed to the standard required; whether defects are the contractor's responsibility or the result of pre-existing conditions; and the final account figure at the end of the project. For projects that are technically domestic (where the client is a residential occupier), the Construction Act adjudication provisions do not automatically apply. The JCT Homeowner Contract includes a voluntary adjudication clause that gives both parties the right to refer a dispute to an independent adjudicator. Adjudication is faster and cheaper than court — typically resolved in 28 days from referral at a cost of £3,000-£8,000 (compared with months or years and tens of thousands of pounds in court). The adjudicator's decision is temporarily binding — it is enforced immediately while either party can later refer the underlying dispute to court or arbitration if they wish to challenge it. Having an adjudication clause in the contract does not mean disputes will end up in adjudication — the existence of a clear dispute resolution mechanism often encourages both parties to negotiate a commercial settlement rather than escalate. For larger disputes or those involving safety or structural issues, independent expert determination or litigation may be more appropriate. Always take legal advice before committing to a dispute resolution route.