Costs
Rear extension costs in 2026
A single-storey rear extension typically costs £1,900–£3,100 per square metre including VAT for a standard specification at our West Midlands baseline, before the kitchen and fees. Here is how that changes by type, region, specification and extras.
How much does each type of rear extension cost per m²?
Guide ranges per square metre of new floor, including VAT, standard specification. Our own regional factors are informed by published 2026 cost guides.
| Region | Single-storey | Two-storey (per m² both floors) | Side return | Wraparound | Glass-led |
|---|---|---|---|---|---|
| London | £2,470–£4,030 | £2,340–£3,510 | £2,990–£4,940 | £2,860–£4,680 | £3,640–£6,240 |
| South East England | £2,130–£3,470 | £2,020–£3,020 | £2,580–£4,260 | £2,460–£4,030 | £3,140–£5,380 |
| East of England | £2,010–£3,290 | £1,910–£2,860 | £2,440–£4,030 | £2,330–£3,820 | £2,970–£5,090 |
| South West England | £1,980–£3,220 | £1,870–£2,810 | £2,390–£3,950 | £2,290–£3,740 | £2,910–£4,990 |
| West Midlands | £1,900–£3,100 | £1,800–£2,700 | £2,300–£3,800 | £2,200–£3,600 | £2,800–£4,800 |
| East Midlands | £1,840–£3,010 | £1,750–£2,620 | £2,230–£3,690 | £2,130–£3,490 | £2,720–£4,660 |
| North West England | £1,790–£2,910 | £1,690–£2,540 | £2,160–£3,570 | £2,070–£3,380 | £2,630–£4,510 |
| Yorkshire and the Humber | £1,770–£2,880 | £1,670–£2,510 | £2,140–£3,530 | £2,050–£3,350 | £2,600–£4,460 |
| North East England | £1,710–£2,790 | £1,620–£2,430 | £2,070–£3,420 | £1,980–£3,240 | £2,520–£4,320 |
| Wales | £1,770–£2,880 | £1,670–£2,510 | £2,140–£3,530 | £2,050–£3,350 | £2,600–£4,460 |
| Scotland | £1,800–£2,940 | £1,710–£2,560 | £2,180–£3,610 | £2,090–£3,420 | £2,660–£4,560 |
| Northern Ireland | £1,650–£2,700 | £1,570–£2,350 | £2,000–£3,310 | £1,910–£3,130 | £2,440–£4,180 |
What do typical sizes cost?
West Midlands baseline, standard specification, including VAT.
| Type | Size | Guide inc VAT |
|---|---|---|
| Single-storey rear extension | 3 m wide × 4 m deep (12 m²) | £23,000–£37,000 |
| Single-storey rear extension | 4 m wide × 5 m deep (20 m²) | £38,000–£62,000 |
| Single-storey rear extension | 4 m wide × 6 m deep (24 m²) | £45,500–£74,500 |
| Two-storey rear extension (per m² across both floors) | 3 m × 5 m footprint, two floors (30 m²) | £54,000–£81,000 |
| Two-storey rear extension (per m² across both floors) | 4 m × 6 m footprint, two floors (48 m²) | £86,500–£129,500 |
| Side return extension | 2 m wide × 6 m deep (12 m²) | £27,500–£45,500 |
| Side return extension | 2.5 m wide × 7 m deep (17.5 m²) | £40,500–£66,500 |
| Wraparound extension | L-shaped, about 22 m² of new floor | £48,500–£79,000 |
| Wraparound extension | L-shaped, about 30 m² of new floor | £66,000–£108,000 |
| Glass-led rear extension | 3 m wide × 4 m deep (12 m²) | £33,500–£57,500 |
| Glass-led rear extension | 4 m wide × 6 m deep (24 m²) | £67,000–£115,000 |
How does specification change the price?
A 20 m² single-storey extension at West Midlands rates, by specification:
| Specification | Typically includes | Guide inc VAT |
|---|---|---|
| Premium | Slim-frame sliders, large lantern, porcelain or engineered oak floors, designer lighting | £46,500–£75,500 |
| Standard (our standard spec) | Aluminium bifolds or sliders up to about 3 m, rooflights, a standard opening into the house, good mid-range finishes | £38,000–£62,000 |
| Essential | uPVC or aluminium French doors, flat rooflight, simple finishes | £34,000–£56,000 |
What extras should you budget for?
| Extra | Guide inc VAT |
|---|---|
| Larger or premium glazing: doors over 3 m wide or slim-frame sliders (extra over standard doors) | £2,500–£8,000 |
| Roof lantern (about 2 m × 1 m), supplied and fitted | £2,200–£4,500 |
| Wider or full-width opening into the house: bigger steels, padstones and making good (extra over the standard opening) | £2,500–£7,000 |
| Kitchen fit-out allowance | £10,000–£25,000 |
| Party wall surveyor allowance (per neighbour, England and Wales) | £700–£1,500 |
Design, approval and council fees
| Item | Guide |
|---|---|
| Planning drawings and application (single-storey) | £1,000–£2,500 |
| Planning drawings and application (two-storey) | £2,000–£3,500 |
| Permitted development drawings and lawful development certificate application | £1,200–£2,500 |
| Prior approval drawings and submission (England) | £1,000–£2,200 |
| Building Regulations drawings and structural calculations (single-storey) | £2,500–£5,500 |
| Building control fee (council or approver, single-storey) | £650–£1,300 |
A householder planning application in England costs £548 (£575 for applications made from 8 December 2026), and a lawful development certificate for proposed work costs half the householder fee. Prior approval in England is £249 (£310 for applications made from 8 December 2026). Wales, Scotland and Northern Ireland set their own fees.
These are guide prices to help you plan. Your written price follows a measured survey and an agreed design, and any items that cannot be priced until the ground is open are shown as provisional sums.
FAQ
Cost questions
What is included in your per m² guide?
The build: foundations, slab, walls, roof, standard doors up to about 3 m wide and rooflights, a standard opening into the house with its steel, electrics, plastering and screed. Wider openings and larger or premium glazing are extras; kitchen fit-out and professional and council fees are separate.
Do your prices include VAT?
Yes, our guide prices include VAT at 20%. Most extension work to an existing home is standard-rated.
Why is the price per m² higher for small extensions?
Fixed costs such as the steel, the knock-through and the roof edge are spread over fewer square metres.
How much contingency should I allow?
10% to 20% of the build cost for things nobody can see until the ground is open, such as drains or soft ground.
What are the council fees in England?
Householder planning £548 (£575 from 8 December 2026); prior approval £249 (£310 from 8 December 2026); building control usually £650–£1,300.