How to check a builder's quote before you sign

What a complete building quote contains, the items most often missing from extension, loft and kitchen quotes, the wording that hides extras, and the questions to ask before paying a deposit.

A low quote is usually an incomplete quote

The most common reason one builder is thousands cheaper than another is not efficiency; it is that the cheaper quote leaves things out. Steels and padstones, drainage, the floor slab, building control fees, the structural engineer, making good, decoration and VAT are the usual absentees on extension quotes. They arrive later as variations, when you have no leverage.

What a complete quote for an extension contains

Site set-up and welfare, scaffolding, skips, strip-out and demolition including breaking through the existing wall, excavation and muck away, foundations with a depth assumption and a rate for going deeper, drainage alterations and any build-over agreement, damp proof course and membrane, the floor build-up (hardcore, insulation, slab, screed), walls with the insulation specified, structural steel and lintels, roof structure and covering with fascias and guttering, windows and doors with the manufacturer named, first and second fix electrics with certification, plumbing and heating extended into the new room, plastering, decoration, external making good, building control fees, the structural engineer's calculations, party wall matters where relevant, a contingency, the VAT position, a programme, a payment schedule tied to completed stages, and insurance and guarantee details.

Wording that hides extras

• "Roof works as discussed": no specification, no quantities, nothing to hold anyone to.
• "Materials": a lump sum with no schedule.
• "Making good": open-ended; ask for it itemised.
• "Prices exclude VAT" with no statement of whether the trader is VAT registered: the real total may be 20 percent higher.
• "Estimate" rather than "quotation": an estimate is not a fixed price.
• A cash price discount that is almost exactly the VAT: no receipt, no paper trail, and weak recourse if the work fails.

Payment terms

A 40 or 50 percent deposit on a job of tens of thousands of pounds is not normal practice. A small deposit for materials on order, then stage payments against completed work, with a retention at the end, is. If a builder insists on most of the money up front, that is the answer to whether to proceed.

Questions to ask before you sign

Is this a fixed price for the whole job or the shell only? Are you VAT registered? Who supplies the steels and who instructs the engineer? Where is the floor in this quote? Are drainage and a build-over agreement allowed for? Who pays building control? What are the start and completion dates, and what happens if it overruns? Can I see your public liability insurance and two recent local references?

Check it in a minute

Upload the quote to Curtilage as a PDF or a photo. It lists every priced line, tells you what a complete quote for that job normally includes but yours does not, flags vague lines and red flags, and writes the questions to ask. It is free while the comparison corpus is being built, and it shows price benchmarks only once it holds enough comparable quotes to be honest about them.

Updated 2026-09-14. Curtilage is not legal advice.