How to quote a kitchen extension without leaving money on the table
A line-by-line walkthrough of a real £35k extension quote: where firms under-price, how to show provisional sums, and the payment plan that protects your cash flow.
Most extension quotes I see are priced well on the big stuff — steel, brickwork, the roof — and quietly lose money on everything around it. The spoil removal that turned into three grab lorries. The worktop the client upgraded twice. The building control visit nobody priced.
This guide walks through a real quote we built for a rear kitchen extension in Bristol: roughly 22m², flat roof with a lantern, knock-through to the existing kitchen. Contract value about £35k including VAT.
1. Structure it the way it'll be built
Group your quote into the sections you'll actually work through on site: groundworks, structure and envelope, kitchen fit, electrics and heating. It reads better for the client, and it means each section can become a payment stage later without rework.
| Section | Ex VAT | Share |
|---|---|---|
| Groundworks & foundations | £4,178 | 14% |
| Structure & envelope | £13,468 | 46% |
| Kitchen installation | £6,635 | 23% |
| Electrics & heating | £4,761 | 17% |
| Total | £29,043 | 100% |
2. Price the lines everyone forgets
These are the items that most often go missing from extension quotes we review. None of them are big on their own. Together they're often your whole margin.
- Spoil removal — price per load, and say how many loads you've allowed.
- Building Control fees and inspection visits.
- Temporary kitchen or protection for the client's existing rooms.
- Making good where the knock-through meets the old house.
- Skip permits and parking suspensions where the council needs them.
3. Be honest about provisional sums
If the client hasn't chosen their worktop, don't guess and absorb the difference. Put in a clearly labelled provisional sum with a note explaining what it covers and when it'll be confirmed. Clients trust a quote more when it tells them where the uncertainty is.
A quote that admits what it doesn't know yet is a quote the client believes about everything else.
4. Mark up per line, not per job
A flat 15% across everything sounds tidy, but it over-prices client-supplied items and under-prices the risky ones. On this job we ran 0% on fitting client-supplied units, 8% on the roof lantern (a supplied item with little risk), and 15% on groundworks, where surprises live.
5. Attach the payment plan to the quote
The time to agree how you'll get paid is before the client signs, not after. We used four stages tied to visible milestones — deposit on booking, groundworks complete, watertight, practical completion — so nobody can argue a stage hasn't been reached.
6. Send it while they're still excited
Speed wins work. A clear quote the evening after the site visit beats a slightly cheaper one a fortnight later. Send it as a link so you can see when it's been opened, and follow up the day after they've read it — not before.