of UK homeowners said the final cost of their renovation exceeded the original quote — by an average of 12%, rising to £2,807 on larger projects.
That gap between quoted price and final bill isn't usually fraud. It's usually the result of assumptions — things the builder expected to be included that weren't, things the homeowner expected to be included that weren't, and decisions made on site that nobody priced in advance.
Understanding a builder's quote before you accept it is one of the most valuable things you can do. It doesn't require construction expertise. It requires knowing what to look for.
What a proper quote should include
A professional, detailed quote for any significant renovation should contain the following elements. If yours is missing several of these, that itself is information worth having.
- A detailed, itemised breakdown — not a single lump sum figure. Each trade, each element of work, each material category should be listed separately.
- A clear scope description — in writing, what is and isn't included. Not just what the builder will do, but what they're explicitly not doing.
- Labour costs shown separately from materials — so you can understand the structure of the pricing and compare meaningfully with other quotes.
- Provisional sums clearly labelled — where the builder doesn't yet know the exact cost of something (e.g. structural engineer's fees, specialist materials), this should be flagged with an estimate and a note that it's subject to change.
- Preliminaries (prelims) itemised — site setup, skips, scaffolding, project management, insurance. These are real costs and a quote that buries them in a contingency line is hiding something.
- A programme or timeline — start date, estimated duration, key milestones.
- Payment terms — stage payments tied to progress, not large upfront sums.
- VAT clearly shown — is the figure inclusive or exclusive? For a £70,000 job, that's a £14,000 difference.
The red flags that matter most
Red flag 1: A single lump sum with no breakdown. According to MyBuildAlly, a quote with no itemisation is the biggest warning sign you can receive. Without a breakdown, you cannot verify whether the pricing is reasonable, negotiate specific elements, or hold the builder to what was agreed if corners are cut.
Red flag 2: Vague language like "works as necessary" or "allowances". These phrases give the builder room to define scope as they go — and charge accordingly. Every line item should be specific. "Kitchen installation" is vague. "Supply and fit of client-supplied kitchen units, including waste connection, tiling to splashback, and boxing in of services" is not.
Red flag 3: PC sums (prime cost sums) that are unrealistically low. A PC sum is a placeholder cost for items not yet specified — for example, sanitaryware or kitchen appliances. A builder can keep their quote total artificially low by using very low PC sums. You pay the actual cost later, as a variation.
Red flag 4: A large upfront deposit. The Federation of Master Builders advises that no more than 10–15% should be paid as a deposit before work begins. A builder asking for 30, 40, or 50% upfront is either in financial difficulty or operating in a way that removes your negotiating position if problems arise.
Red flag 5: A quote that arrived very quickly. A detailed, accurate quote for a significant renovation takes time to prepare. A builder who submits a quote the next day after a brief site visit has either templated it loosely or hasn't priced it properly. Both lead to problems later.
What's almost always excluded — and rarely flagged
The items below appear on final bills with regularity. They almost never appear in a builder's quote unless specifically requested:
- Building Control fees and inspections
- Party wall surveyor fees (required when building near a boundary or on a semi-detached or terraced property)
- Utility diversions — gas, drainage, electricity
- Structural engineer's fees
- Internal decoration after building work is complete
- Skip hire beyond the initial allowance
- Temporary accommodation costs if the property becomes uninhabitable
On a £60,000 kitchen extension, these exclusions can add £5,000–£12,000 to the final cost. They are not surprises to a builder — they are simply items that, if excluded from the quote, remain the homeowner's problem to discover and fund.
How to compare quotes properly
The standard advice — get three quotes and choose the middle one — is not enough. Two quotes for the same project can differ by 30–40% while pricing completely different scopes. The only meaningful comparison is a like-for-like one.
Before inviting quotes, prepare a written brief or specification. Include: what you want done, in what materials, to what standard, by when. Send the same document to every builder you approach. You then receive quotes that are at least attempting to price the same job — and the differences become meaningful rather than arbitrary.
Once you have multiple quotes, build a simple spreadsheet. List every line item from the most detailed quote down the left column. Map each builder's pricing across. The gaps — where one builder has included something and another hasn't — are exactly where the risk lives.
What to ask before you accept
Before signing anything, these are the questions worth putting in writing:
- Is this a fixed-price quote, or is it subject to material price increases?
- Are Building Control and party wall costs included or excluded?
- What is your process for raising variations, and how will they be agreed and authorised?
- What payment milestones are you proposing, and what triggers each stage payment?
- Who will be on site day to day, and will you be directly managing the project?
- What is your approach if the programme runs over the agreed timeline?
A good builder will answer these questions clearly and without hesitation. The answers will tell you as much as the quote itself.
Have a quote you want reviewed independently?
Renovate Better offers builder quote review as a dedicated service. We go through your quotes line by line — identifying what's missing, where assumptions differ, and what to clarify before you commit.
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