One fixed price for the whole job — not the hours

Single-Storey Extension Fair Price

Typical trade: builder. Move the sliders and answer the questions.

Describe the job or snap a photo — AI fills in the sizes

Roof type
How finished?
Bi-fold / sliding doors?
How easy is access and parking?

Fair fixed price for the whole job

£60,450

Fair range: £53,196 – £71,331

20 m² extension

Realistic time on site

35.6 days

Crew / total hours

3 · 800.0 h

Labour (800.0 h × £40)
£32,000
Materials
£23,500
Architect drawings & structural engineer
£2,800
Building control fees
£950
Skips over the build
£1,200

Over £89,164? Ask why in writing.

  • Weekly 'day rate' payments with no fixed scope
  • Asking for 30%+ upfront
  • No building-control sign-off

Insist on

  • One written fixed price for the full scope — no open-ended hours.
  • Deposit of 10–20% at most; balance after you inspect the work.
  • Any extra work agreed and priced in writing before it starts.
  • Agree staged payments tied to milestones (foundations, watertight, first fix, completion) — never weekly payments.
  • Typical programme: 8–12 weeks for 20 m², 12–16 weeks for 40 m²+.

Estimate for an experienced, insured tradesperson. Local prices vary — adjust the hourly rate for your area.

Powered by Calcurly.com