My builder has left the job unfinished: what can I do?

Few things on a building project are as stressful as a half-built extension and a builder who has stopped answering the phone. The good news is that there is a sensible order in which to deal with it. The order matters: what you do in the first couple of weeks can make a real difference to how much it costs to finish the job, and to whether you can recover that extra cost later.

This guide is written for homeowners in England and Wales who employed a builder directly. It explains the practical steps a quantity surveyor would take, starting with the facts and the documents.

1. First, work out whether the builder has really left

Builders sometimes stop work for a few days because materials are late, another job has overrun or they are waiting for a payment or a decision from you. That is frustrating, but it is not the same as abandoning the job. Before taking any formal step, ask yourself:

• How long has it been since anyone worked on site, and has the builder given any reason?
• Have tools, plant, skips and materials been removed?
• Is there an unpaid invoice, a disputed variation or an instruction the builder is waiting for from you?
• Does your contract or quotation say anything about the programme, completion date or stopping work?

Be honest about the last point. If the builder has stopped because an invoice that was properly due has not been paid, the position may be very different, and you should deal with that first.

2. Gather your documents

Put everything in one place, in date order: the quotation or estimate, any written contract (for example a JCT Homeowner contract), drawings and specifications, every invoice and receipt, bank records of what you have paid, and texts, emails and WhatsApp messages. Notes of conversations, with dates, are useful too. If changes or extras were agreed along the way, list them and how they were priced.

The question you are trying to answer is simple: what did the builder agree to do, for what price, by when, and what has been paid?

3. Record the state of the work, today

Before anything else is touched, take dated photographs and video of every area of the work, inside and out. Show what is finished, what is part-done and what has not been started. Photograph materials left on site. If you can, ask an independent person to walk round with you and keep a short note.

This record matters because once another builder starts, the evidence of what the first builder actually did disappears under new work. Disputes about unfinished jobs are very often disputes about value, and value depends on being able to show what was there.

4. Put it in writing, calmly

Write to the builder, by email and, if you have an address, by recorded post. Keep it factual and polite. Say that work stopped on a given date, ask them to confirm by a stated date whether they intend to return and finish, and ask for a realistic date by which the work will be completed. Seven to fourteen days is commonly given, depending on the circumstances. Say that if you hear nothing, you will have to arrange for others to complete the work and will hold them responsible for the extra cost.

Avoid threats, insults or social media posts. Your letters may later be read by a mediator, adjudicator or judge, and you want them to show you behaving reasonably.

5. Understand your rights in outline

When a builder contracts with a consumer, the Consumer Rights Act 2015 implies terms into the contract. In particular, the service must be performed with reasonable care and skill (section 49) and, where no time has been fixed, within a reasonable time (section 52). If those terms are broken, the Act gives you the right to ask for the work to be put right and, where that is not possible or not done within a reasonable time, a right to an appropriate price reduction. You also keep the general right to claim damages for breach of contract.

If a builder walks off the job without good reason and shows they do not intend to finish, that may amount to a serious (repudiatory) breach of contract. In that case you may be entitled to bring the contract to an end and claim the reasonable extra cost of having someone else finish the work. Whether a particular situation reaches that threshold depends on the facts and the contract wording, and getting it wrong can put you in breach. This is the point at which it is worth taking advice, and legal advice if a claim is likely.

Two other points are worth knowing. The payment rules in the Housing Grants, Construction and Regeneration Act 1996 (the "Construction Act") generally do not apply to contracts with a residential occupier for work on their own home, so the notices and rights you may read about in trade forums usually do not apply to you unless your written contract includes them. And if your contract has its own termination clause, follow its notice procedure exactly.

6. Work out what the work done is actually worth

This is the step most homeowners skip, and it is the one that usually decides the outcome. Compare what you have paid with the fair value of the work properly carried out, item by item, using the quotation as the starting point. Deduct anything defective or missing. Account for materials you paid for that are on site, or that have gone.

Most unfinished jobs fall into one of three positions:

• You have overpaid: paid more than the work is worth. You may have a claim to recover the difference, plus the extra cost of completion.
• You are about even: the main issue is the extra cost of getting someone else to finish at today's prices.
• You owe money: the builder may have a claim against you for work done, which can be set against your own claim.

An independent valuation by a quantity surveyor gives you a figure you can rely on, explain and defend, rather than an estimate drawn up in anger.

7. Getting the job finished

Once you have given the builder a fair chance to respond and recorded the position, you can ask other builders to price the completion work. Give them the same written scope so the quotes can be compared. Keep the cost of completion separate from the cost of putting right defective work, as they may need to be shown separately later.

Check whether your local authority Building Control or an approved inspector was involved. Building regulations sign-off may be outstanding and the new builder will need to know what inspections have taken place. Also check whether you paid any deposit by credit card (section 75 of the Consumer Credit Act 1974 can make the card provider jointly liable where the price is between £100 and £30,000), whether the builder belongs to a trade association with a dispute or guarantee scheme, and whether any insurance-backed guarantee was provided.

Do your best to keep the cost of completion reasonable. You are generally expected to take reasonable steps to limit your loss, so a much more expensive specification is unlikely to be recoverable.

8. Recovering your money

With the records and a valuation in hand, you can set out your claim in a clear letter before action. Court rules in England and Wales expect parties to exchange information and try to settle before issuing proceedings, and mediation is often a quicker and cheaper route. For lower-value claims, the County Court small claims track is designed for people acting without a lawyer. Bear in mind that a judgment is only as good as the builder's ability to pay, so it is worth checking whether the business is still trading before spending heavily.

Common mistakes to avoid

• Letting a new builder start before the work has been recorded.
• Paying more money in advance to persuade the builder to come back.
• Withholding sums that are genuinely due and then calling it abandonment.
• Throwing away or using the original builder's materials without keeping a record.
• Letting the dispute drift. Memories fade and costs rise.

How Building Contract Clinic can help

I am Malcolm Blackburn AssocRICS, a quantity surveyor with 44 years of experience in construction costs, contracts and final accounts. In a fixed-fee £150 initial consultation we can go through your quotation, payments and photographs, identify where you stand and agree the sensible next steps. If further work would help, such as a valuation of the work done or a cost-to-complete assessment, I will tell you the scope and fee before you decide whether to go ahead.

Important: This guide is general information about practice in England and Wales as at the date shown. It is not legal advice and does not take account of your particular contract or circumstances. Where legal rights, deadlines or court proceedings are involved, take advice from a qualified solicitor. Building Contract Clinic provides quantity surveying, cost and building contract support.