Why the Cheapest Builder Quote Can Cost More Later

1. The cheapest quote is rarely the same job

When three UK builders quote different prices for the "same" extension, patio or renovation, they are almost never quoting for the same work. The cheapest number on the page usually has less inside it: thinner foundations, fewer steels, no waste removal, no scaffolding, no making good. You're not comparing prices — you're comparing different jobs that happen to share a job title.

2. Missing scope is the most common hidden cost

Scope gaps are the number-one reason a "cheap" quote balloons later. Watch for vague lines like "all associated works", "as discussed", or a single total with no breakdown. If a builder cannot tell you what is and isn't included in writing, the gap will be filled later — and always at your expense.

3. VAT can quietly add 20% to the bill

Some UK builders are VAT registered, some aren't. A quote excluding VAT can look 20% cheaper than one including it. Always ask whether the figure is inclusive or exclusive of VAT and whether the builder is VAT registered. Compare like-for-like, or you'll compare £40,000 with £48,000 and not know it.

4. Provisional sums hide real numbers

A £4,000 "kitchen allowance" or £2,000 "electrics provisional sum" is an estimate, not a fixed price. In practice these almost always land higher. The cheap quote often uses low provisional sums to look competitive on paper.

5. Weak payment terms transfer risk to you

Large up-front deposits, front-loaded stage payments, or "pay before delivery" terms move risk away from the builder and onto you. If anything goes wrong, you have already paid for work you don't yet have. A sensible UK payment schedule ties money to completed, inspected stages with a small retention held back for snagging.

6. Variations and "extras" make up the difference

The cheap headline figure often turns into the expensive final figure through variations: "we found rot", "the steel had to be bigger", "you wanted that re-skimmed". Some are genuinely unforeseen. Many are scope that should have been priced up front.

7. How to compare quotes properly

Score quotes on the same lines: scope, materials, VAT, payment schedule, provisional sums, exclusions and timings. Send the same clarification questions to every builder. The free Builder Quote Checklist covers the basics; the Homeowner Quote Checker Pack gives you a scoring grid, comparison sheet and a polite clarification email template you can send before you commit.

The Builder's Brief UK provides practical homeowner guidance based on real trade experience. It is not legal, financial, architectural, structural engineering, planning or building-control advice, and is not a replacement for project-specific guidance from suitably qualified professionals.