Cost guide
How much does a builder cost?
Building work is quoted per square metre of finished space, or as a fixed contract sum with a staged payment schedule.
- Typical day rate
- £280–£450
- Smallest job
- from £2,200
- Priced jobs
- 4
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Pick what you need — we'll price it at current builder rates.
What each job costs
| Job | Unit | Typical price |
|---|---|---|
| Single-storey rear extensionShell to finished, excluding kitchen and bathroom fittings. | per m² | £2,200–£3,400 |
| Loft conversionDormer and en-suite included; hip-to-gable costs more. | per conversion | £42,000–£78,000 |
| Knock through with a steel beamIncludes structural calculations and building control. | per opening | £3,000–£6,500 |
| Garage conversionInsulation, damp proofing and a new floor are the bulk of it. | per conversion | £9,000–£20,000 |
Ex VAT. South East baseline — the calculator adjusts for your region.
Keeping the cost down
- Never pay a large deposit up front — stage payments against completed work.
- Budget 10–15% contingency; nobody knows what is under the floor.
- Fees for architect, structural engineer and building control add 10–15%.
Common questions
- Do I need planning permission?
- Many extensions fall under permitted development, but you still need building regulations approval. Confirm with your council before starting.
- How long does an extension take?
- Twelve to twenty weeks on site for a typical single-storey rear extension.
Ready for real numbers?
Describe the job once and vetted builders come back to you with priced quotes. Free, and no obligation.