A typical price
3 m out × 3 m wide
- London (outer)
- £31,000 to £39,700
- South East
- £30,200 to £38,700
- Midlands
- £29,100 to £37,300
- North of England
- £28,800 to £36,900
4 m out × 5 m wide
- London (outer)
- £41,400 to £53,000
- South East
- £40,100 to £51,400
- Midlands
- £38,400 to £49,200
- North of England
- £37,900 to £48,600
5 m out × 6 m wide
- London (outer)
- £50,500 to £64,700
- South East
- £48,900 to £62,600
- Midlands
- £46,700 to £59,800
- North of England
- £46,000 to £58,900
| Size | London (outer) | South East | Midlands | North of England |
|---|---|---|---|---|
| 3 m out × 3 m wide | £31,000 to £39,700 | £30,200 to £38,700 | £29,100 to £37,300 | £28,800 to £36,900 |
| 4 m out × 5 m wide | £41,400 to £53,000 | £40,100 to £51,400 | £38,400 to £49,200 | £37,900 to £48,600 |
| 5 m out × 6 m wide | £50,500 to £64,700 | £48,900 to £62,600 | £46,700 to £59,800 | £46,000 to £58,900 |
Including VAT, for: rear, flat roof, brick, 3 m bifold doors, no knock-through. Priced 6 October 2026 on published UK rates. A guide, not a quote.
More than it looks
The middle-size job above is 45 tasks, about 9 weeks on site:
- Prep and strip-out · 1
- Groundworks · 11
- Structure · 7
- Roof and windows · 9
- First fix: pipes and cables · 3
- Plaster, insulation, floors · 5
- Finishes and second fix · 7
- Outside · 2
Plus site costs: scaffold, skips, building control, site toilet, site fencing, insurance, supervision, dust protection, cleaning, electrical certificate.
- The first weeks are underground: digging, foundations, drains.
- The ground decides the foundations, and you only know once it’s dug.
- Opening into the house needs a steel and propping.
What changes the price
Size
- Why it moves the price
- More wall and roof, not just floor
- Ask
- “What size have you priced?”
The ground
- Why it moves the price
- Soft ground means deeper foundations
- Ask
- “What if they need to go deeper?”
Doors and glass
- Why it moves the price
- A big part of the price
- Ask
- “Which doors have you priced?”
Access
- Why it moves the price
- No side access means it’s all by hand
- Ask
- “How will you get to the back?”
| What | Why it moves the price | Ask |
|---|---|---|
| Size | More wall and roof, not just floor | “What size have you priced?” |
| The ground | Soft ground means deeper foundations | “What if they need to go deeper?” |
| Doors and glass | A big part of the price | “Which doors have you priced?” |
| Access | No side access means it’s all by hand | “How will you get to the back?” |
Paperwork and certificates
- Planning permission, or a permitted development check
- Building regulations sign-off
- Party wall notices near the boundary
Questions to ask for this job
- Who does the drawings?
- What if the foundations go deeper?
- Is opening into the house included?
What would your job cost?
Describe it, and see a typical price for your area. Then ask builders who do this work.
Read next
How we wrote this
Written by Structa; prices from Structa’s engine, 6 October 2026. The rules come from the official pages below. General information, not legal advice.
- GOV.UK: Planning permission (checked 6 October 2026)
- GOV.UK: When you need building regulations approval (checked 6 October 2026)
- GOV.UK: Party walls and building work (checked 6 October 2026)