The contract is where good builds are won and bad builds are lost. Before you sign with any UK builder in 2026, check five things line by line: is the price fixed or an estimate, is every payment tied to a completed stage (never a calendar date), are start and completion dates stated, how are variations priced (in writing, before the work), and does the legal entity on the contract match the company you actually vetted. This guide walks through the full checklist — the standard contract forms to ask for (JCT Home Owner, FMB Domestic), sensible deposit and retention numbers, and the red flags that mean you should walk away no matter how good the price looks.
Five things decide most disputes: (1) fixed price or estimate — and which lines are provisional sums; (2) a stage-linked payment schedule where you only ever pay for completed, inspectable work; (3) written start and completion dates; (4) a variations clause requiring written pricing before any extra work; (5) the exact legal entity named on the contract, matching the company you vetted at Companies House.
Benchmarks for 2026: deposit 5–10% (protected), retention 2.5–5% released after snagging, public liability £2m+, and a recognised standard form — the JCT Home Owner Contract or FMB Domestic Building Contract — rather than two paragraphs on a quote.
Work through every point on every contract — ten minutes here saves five-figure disputes later.
The contract must name the builder's registered legal entity — not a trading name. Check it at Companies House: incorporation date, filing history, and whether it matches the firm whose reviews and references you actually vetted.
The scope should reference the drawing numbers, spec document and revision dates. “Build extension as discussed” is not a scope — it is a blank cheque for disagreement about what was included.
A fixed price only moves via written variations. Provisional sums (groundworks) and PC sums (kitchen supply) can move — cap them and require written approval before they are exceeded.
Each payment tied to a completed, inspectable stage — foundations, wind-and-watertight, first fix, completion. Never calendar dates. You should always be behind the work, not ahead of it.
A modest deposit is normal; 25%+ is not. Ask how it is protected: insurance-backed deposit scheme, TrustMark business, or pay it by credit card for Section 75 protection.
Both dates in writing, plus what constitutes legitimate delay (weather, discovered conditions, your own variations) and what happens on overrun. No dates = no accountability.
Every change priced in writing and signed off before it is built. Verbal extras “sorted at the end” are the single most common cause of five-figure final-bill shocks.
Public liability of £2m+ named in the contract with the insurer, plus any structural warranty or insurance-backed guarantee on the work. Ask to see the certificate — and check the dates.
Retention released after the defects period (3–6 months) is your only real lever on the last snags. Reasonable builders accept it; blanket refusal on a big job is a warning sign.
A mediation/adjudication clause beats going straight to court. Signed in your home? The Consumer Contracts Regulations give you a 14-day cooling-off right — the builder must tell you about it.
The three pricing bases you will see on 2026 contracts — and when each one is legitimate.
| Basis | Can the price move? | Legitimate for | Watch for |
|---|---|---|---|
| Fixed price | Only via written variations | Defined scopes: extensions, lofts, refits with drawings | Uncapped provisional sums buried in the appendix. |
| Estimate | Yes — it is a best guess | Genuinely unknown scope: structural repair, discovery work | “Estimates” used to win the job, then re-priced at 30%+ once started. |
| Day rate | Yes — time and materials | Small repairs and short jobs (£200–£320/day per trade typical in 2026) | No daily cap, no evidence of hours, materials marked up without receipts. |
Most well-run domestic jobs in 2026 use a fixed price with capped provisional sums. See also: how to get genuinely fixed-price quotes.
You do not need a solicitor to get a professional contract — two standard forms cover almost every domestic job.
Any two of these together and no price is good enough.
Complete your due diligence with the rest of the series.
The questions to ask past customers — and how to spot fakes.
Public liability, employer's liability and what the certificate must show.
The patterns rogue firms repeat — and the checks that expose them.
BestBuilders matches you with up to 3 vetted UK builders who quote in writing and work to proper contracts. Compare real prices, check reviews, and hire with confidence — all for free.
The 8 questions UK homeowners ask most often in 2026.
At minimum: the exact legal names of both parties, a defined scope of works with drawings and spec referenced, a fixed price or transparent pricing basis, a stage-linked payment schedule, start and completion dates, a written variations procedure, insurance details, warranty terms, snagging/retention terms and a dispute-resolution clause.
A signed, accepted quote can form a contract — but it usually leaves the important terms (payment stages, variations, delays, defects) undefined, which is where disputes start. For anything beyond a small repair, put a proper written contract on top of the quote. The JCT Home Owner Contract and the FMB Domestic Building Contract are inexpensive standard forms designed for homeowners.
Typically 5–10% of the contract value, and many established firms ask for nothing beyond materials on order. Treat a demand for 25%+ upfront, or full payment before completion, as a serious red flag. Where a deposit is taken, ask whether it is protected — through an insurance-backed scheme, a TrustMark-registered business or payment by credit card (Section 75 protection on amounts over £100).
A fixed price commits the builder to a total for a defined scope — it can only move via written variations. An estimate is a best guess and can legitimately rise. Contracts often mix the two: a fixed price for the main works plus provisional sums for unknowns like groundworks. Cap provisional sums and require written approval before they are exceeded.
It ties each payment to a completed, inspectable stage — foundations poured, shell wind-and-watertight, first fix done, completion — rather than calendar dates. You should always be paying for work already done, never funding work not yet started. If the schedule ever runs ahead of the build, you lose all leverage and carry all the risk of the builder failing.
A small slice of the price — usually 2.5–5% — held back at practical completion and released once snagging is done, often after a 3–6 month defects period. It is your only real lever to get the last defects fixed. Established builders accept reasonable retention without fuss; refusal to countenance any retention on a large job is a warning sign.
Cash-only pricing, no written contract for a five-figure job, a deposit over 25%, payment schedules running ahead of the work, a contract naming a different company than the one you vetted, no insurance details, 'variations to be agreed on site' with no pricing mechanism, and pressure to sign on the day for a 'discount'. Any two of these together: walk away.
Usually yes — if the contract was signed away from the builder's business premises (i.e. in your home, which is typical), the Consumer Contracts Regulations give you a 14-day cooling-off right, and the builder must tell you about it. If work starts within those 14 days at your request, you may owe for work done. A builder who 'forgets' to mention cancellation rights is telling you something.