10 Rules for Checking a
Builder’s Quote (BOQ)
The Bill of Quantities is the single most important document in your project — and the one homeowners understand least. Read it right and you’ll spot the gaps before they cost you thousands.
First — what is a BOQ?
A Bill of Quantities (BOQ) is the itemised breakdown behind a builder’s price. Instead of one big number, it lists every element of the work — with a description, quantity, unit, rate, and line total — so the whole job adds up in front of you.
A real BOQ is the homeowner’s best protection. It’s how you compare builders fairly and stop a low headline price quietly climbing once work starts.
| Item | Qty | Unit | Rate | Total |
|---|---|---|---|---|
| Single-ply roof to rear extension | 18 | m² | £145 | £2,610 |
| Crittall-style steel doors (supply & fit) | 1 | set | £8,400 | £8,400 |
| Underfloor heating to extension | 22 | m² | £95 | £2,090 |
| Section subtotal | £13,100 |
The 10 Rules
Run any builder's quote through these ten checks before you sign. Don't judge on the bottom line — judge on what's behind it.
Is every item priced — or just listed under one total?
Why it matters: “Itemised” means each item carries its own price — not a long list of works followed by a single lump sum at the bottom. A list with one total looks detailed but tells you nothing.
How to check: Run your finger down the page — does every line have its own rate and total beside it? If the descriptions fill a page but the only figure is “£95,000” at the end, it isn’t itemised.
Do the quantities match your actual project?
Why it matters: Understated quantities are the classic trick — a lower headline price that grows the moment real measurements are used.
How to check: Cross-check the key quantities against your architect’s drawings — floor area (m²), wall area, roof area, number of windows/doors. If the BOQ says 15m² and your extension is 22m², the price is fiction.
Read the exclusions before you read the total.
Why it matters: The cheapest quote is usually cheapest because something’s been left out. The exclusions list is where the real price hides.
How to check: Look for what’s excluded: VAT, scaffolding, skips/waste, structural steel, building-control fees, party wall, making good, decoration, kitchen, appliances, worktops. Each exclusion is a bill coming later.
Are the Preliminaries (“Prelims”) shown?
Why it matters: Prelims — site set-up, management, supervision, welfare, insurance, scaffolding, skips, protection — are often 10–20% of a job. If they’re missing, they’ll either appear later or get cut on site.
How to check: Find the prelims section. A serious BOQ has one. No prelims on a £100k job is a warning sign, not a saving.
How many Provisional & PC Sums — and how big?
Why it matters: Provisional sums are allowances for work not yet defined; PC sums are allowances for items you’ll choose later (kitchen, tiles, sanitaryware). Too many large ones mean the “price” is really a guess that will move.
How to check: Add up the provisional/PC sums. If they’re a big slice of the total, ask what each one assumes — and pin down the ones you can.
Are materials specified — make, model, grade?
Why it matters: “Allow for kitchen” lets a builder fit the cheapest unit, or charge a variation when you want quality. The rate means nothing without the spec behind it.
How to check: For the big-ticket items, is there a specification (brand, model, thickness, finish)? “20mm quartz worktop, [brand]” is checkable; “worktop — allow” is not.
Is a programme and a stage-payment schedule attached?
Why it matters: A price means little without a timeline and a fair way to pay. Front-loaded payments or no programme leave you exposed if things go wrong.
How to check: Is there a realistic programme (weeks per stage) and payments tied to completed, signed-off stages — not big sums up front?
Supply-and-fit, or fit-only? Check who’s buying the materials.
Why it matters: A rate can look low simply because it’s labour only — you’re expected to buy and deliver the materials yourself. Mix up “supply & fit” and “fit only” across quotes and you’re comparing two completely different prices.
How to check: For each major element, is the rate supply-and-fit or fit-only? Make sure kitchens, tiles, sanitaryware, worktops and appliances sit clearly on one side — and the same way across every quote you compare.
Is VAT shown — and shown correctly?
Why it matters: VAT is the most common “surprise” on a domestic quote. A price that looks competitive can be 20% short if VAT is tucked away in the small print.
How to check: Is VAT shown clearly as a line, and is the quoted total inclusive? Most renovation work is 20%; some projects qualify for reduced or zero rates. A price quietly marked “+ VAT” is a 20% jump waiting to happen.
Do the numbers actually add up?
Why it matters: Sloppy arithmetic, double-counted items or “TBC” lines are a sign of a rushed, unreliable price — and unreliable pricing means unreliable building.
How to check: Tick that the line totals sum to the section subtotals, the subtotals to the grand total, VAT is added correctly, and nothing reads “to be confirmed.” If the maths is loose, so is the builder.
Good BOQ vs. red-flag BOQ
A BOQ you can trust
- ✓Every item priced individually, not one total
- ✓Quantities match the drawings
- ✓Clear “included / excluded” list
- ✓Site set-up / scaffolding / skips priced
- ✓Few, well-defined provisional sums
- ✓Specification behind the big items
- ✓“Supply & fit” clear — you know who buys what
- ✓Programme + weekly stage payments in arrears
- ✓VAT shown clearly; the maths checks out
Walk-away warning signs
- ✕A list of works with one total at the bottom
- ✕Quantities lower than your real project
- ✕Long or hidden exclusions list
- ✕No site set-up or management priced
- ✕Huge “provisional” / “allow” sums
- ✕“Kitchen — allow”, no spec anywhere
- ✕Vague “supply” — unclear who buys materials
- ✕Big deposit up front, no programme
- ✕“+ VAT” in small print; totals don’t add up
“We were called in after a homeowner had already paid more than half the price of their extension — only for us to find the steel was undersized and the roof had to come off. Every warning sign was in the original quote: no real breakdown, quantities that didn’t match the drawings, and a large payment taken up front. Twenty minutes spent checking that BOQ would have saved them tens of thousands.”
Real people. Real estimators.
Your quote isn't fed into a black box — it's read by the people who price and build 2VP's own projects.
Vladimir Castravet
Founder of 2V Projects and the estimator behind our London builds. Vladimir has spent years pricing — and rescuing — extensions, lofts and renovations, so he knows exactly what every line of a quote should say.
Nicholas Elias
RIBA Silver Medal-winning architect who leads 2VP's design. Nick checks that a quote's scope and drawings actually match — the gap where most homeowners get caught.
Got a quote already? Send it — we’ll check it free.
Our estimators will run your builder’s quote through all ten rules and send you a clear, written summary of exactly where the gaps are — usually within 48 hours.
🔒 We never share your details or your quote. Email your file to hi@2vp.uk.
Trusted by London homeowners & architects.
“Vladimir put together a team of talented, hard-working professionals with a ‘can-do’ attitude and attention to detail. We couldn’t be more pleased with the results!”
“We’re an architecture company that worked with 2V Projects on a rear extension and refurbishment. It felt that builder, client and design team were all invested in producing the best building possible — which is not always the case in this industry!”
“I was, and still am, very happy with the work that was done and would very happily use them again. I cannot recommend them highly enough.”
Estimating is what we do.
2VP prices and builds London projects — with our own glazing and joinery workshops, so we know exactly what every line should cost.
Know exactly where you stand — before you sign.
Send us your quote for a free review, or get a realistic estimate for your own project. Either way, you’ll know your number.
Learn to read a builder’s quote like a quantity surveyor.
A free, plain-English guide from a London design & build team that prices London work every week — 10 rules to spot the gaps before they cost you thousands.
- ✓What a real, itemised BOQ must contain
- ✓The exclusions and “provisional sums” that hide the true price
- ✓How to compare quotes like-for-like
- ✓A free, no-obligation review of a quote you already have
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