Two Storey Extension Cost UK (2026): Prices, per m² & Planning
Quick answer
A two storey extension in the UK typically costs £1,950–£2,400 per m² of total floor area for a standard finish in 2026, excluding VAT. A 40m² double storey extension (20m² on each floor) costs about £76,500–£94,000 to build, or around £97,500–£126,000 all-in with fees, planning and VAT outside London. In London, budget roughly £123,500–£159,000 for the same project.
- Cost per m² (ex VAT): £1,600–£1,950 basic, £1,950–£2,400 standard, £2,400–£3,100 high-end
- Typical 40m² two storey rear extension: £97,500–£126,000 inc. fees and VAT (Midlands)
- Per m² vs single storey: around 10–15% cheaper, because foundations and roof serve two floors
- Planning: two storey side extensions always need permission; some rear ones are permitted development
Want a figure for your own project? Enter the total floor area across both storeys, your finish level and region to get an instant estimate.
Double storey extension cost per m²
Builders and quantity surveyors price a double storey extension by the square metre of total new floor area – the ground floor plus the first floor. So a 4m × 5m footprint built on two levels is 40m², not 20m². That matters, because a two storey extension looks expensive as a total figure but is usually the best value per m² of any extension type.
The reason is simple: the most expensive parts of an extension are the foundations and the roof. On a two storey extension, the same foundations and the same roof serve twice the floor area. The extra cost of the first floor is mostly walls, a floor structure, windows and internal finishes.
| Finish level | Cost per m² (ex VAT) | What it typically includes |
|---|---|---|
| Basic | £1,600 – £1,950 | Brick and block, matching pitched roof, uPVC windows, standard French doors, simple bathroom or bedrooms |
| Standard | £1,950 – £2,400 | Better windows, bi-fold or sliding doors downstairs, rooflights, mid-range flooring and sanitaryware |
| High-end | £2,400 – £3,100 | Large aluminium glazing, structural steel for open-plan layouts, underfloor heating, en-suite, premium finishes |
Published figures vary more for this type of extension than most, so it is worth knowing where the range comes from. Homebuilding & Renovating puts double storey extensions at £2,000–£3,200 per m² (standard to excellent spec, ex VAT), BestBuilders at £1,900–£2,900 per m², MyBuilder at £1,650–£3,000 per m² and the HomeOwners Alliance at around £1,900 per m² for a standard finish. MyJobQuote and the Federation of Master Builders quote lower figures (from about £1,000–£1,300 per m²), but those tend to reflect basic builds, larger footprints or the structural shell rather than a finished, decorated extension. Treat anything under £1,600 per m² with caution unless your quote clearly excludes items like glazing, kitchens and finishes.
Two storey extension cost by size
The table below uses the standard-finish rate. The all-in column is what our calculator produces for the Midlands (close to the UK average) and includes design fees, a structural engineer, building control, a householder planning application and 20% VAT.
| Total floor area | Example footprint | Build cost (ex VAT) | All-in inc. fees, planning & VAT |
|---|---|---|---|
| 20m² | 2.5m × 4m on two floors | £38,000 – £47,000 | £49,500 – £65,500 |
| 30m² | 3m × 5m on two floors | £57,500 – £70,500 | £73,500 – £95,500 |
| 40m² | 4m × 5m on two floors | £76,500 – £94,000 | £97,500 – £126,000 |
| 50m² | 5m × 5m on two floors | £95,500 – £117,500 | £121,000 – £156,000 |
| 60m² | 5m × 6m on two floors | £114,500 – £141,000 | £145,000 – £186,000 |
For comparison, BestBuilders’ August 2026 guide gives £88,000–£136,000 for a fully finished 40m² two storey extension including fees, which sits comfortably around our range. Very small two storey extensions are the least efficient: scaffolding, a crane or hoist, steelwork and planning costs are similar whether you add 20m² or 40m², so the per-m² rate creeps up as the size goes down.
Double storey extension cost by specification
Here is how the finish level changes the price of a typical 40m² double storey extension in the Midlands, including fees, planning and VAT:
| Finish | Build cost (ex VAT) | All-in total |
|---|---|---|
| Basic | £62,500 – £76,500 | £80,000 – £103,000 |
| Standard | £76,500 – £94,000 | £97,500 – £126,000 |
| High-end | £94,000 – £121,500 | £119,500 – £161,000 |
If the ground floor becomes a kitchen, add the cost of the kitchen itself: roughly £8,000–£15,000 for a budget kitchen, £15,000–£30,000 mid-range and £30,000–£50,000 high-end, fitted. A new bathroom or en-suite upstairs typically adds £4,500–£9,000 according to MyJobQuote’s October 2026 figures. See our kitchen extension cost guide for a detailed breakdown.
Two storey side extension cost vs rear extension cost
Two storey rear extension cost
A two storey rear extension is the most common layout: a bigger kitchen-diner or family room downstairs and an extra bedroom or larger bedroom with en-suite above. Because it is usually a simple box with a roof tied into the existing house, it tends to sit in the middle of our per-m² ranges. A typical 30–40m² two storey rear extension costs £73,500–£126,000 all-in outside London at a standard finish.
Two storey side extension cost
Two storey side extensions are popular on semi-detached and detached houses with a driveway or strip of land to the side. Per m², they often cost a little more than rear extensions. MyBuilder notes that side extensions usually need extra structural work, and they are often narrow, so you pay for a lot of external wall relative to the floor area gained. You may also need to rebuild or reroute side drainage, deal with a boundary wall and, if you lose a garage, re-provide parking.
MyJobQuote’s September 2026 guide gives £45,000–£65,000 for a small double storey side extension. On our figures, a 2.5m-wide side extension running 7m deep on two floors (35m²) would cost about £67,000–£82,500 to build at a standard finish, or £85,500–£110,500 all-in in the Midlands. Two storey side extensions are also the type most likely to face design conditions from planners, such as setting the first floor back from the front wall to avoid a “terracing” effect with next door.
Adding a storey over an existing extension
If you already have a single storey extension, building a first floor on top of it can be the cheapest way to add a bedroom. The Federation of Master Builders describes adding a bedroom above an existing kitchen extension as a cost-effective option, because foundations and services are already in place. MyJobQuote suggests £20,000–£30,000 for a simple conversion of this kind. The catch is the existing foundations: a structural engineer must confirm they can carry the extra load, and if they cannot, underpinning can wipe out much of the saving.
Two storey extension costs by region
Labour, access and waste disposal costs vary sharply across the UK. These figures apply our regional multipliers to the standard-finish rate:
| Region | Standard spec per m² (ex VAT) | 40m² two storey, all-in |
|---|---|---|
| London | £2,440 – £3,000 | £123,500 – £159,000 |
| South East | £2,180 – £2,690 | £111,000 – £143,000 |
| South West & East of England | £2,030 – £2,500 | £103,000 – £133,000 |
| Midlands | £1,910 – £2,350 | £97,500 – £126,000 |
| North of England & Wales | £1,790 – £2,210 | £91,500 – £118,500 |
| Scotland & Northern Ireland | £1,870 – £2,300 | £95,500 – £123,500 |
MyJobQuote’s regional data points the same way, putting Greater London at 20–40% above the UK average and the South East 10–25% above, with Wales 10–15% below.
Full cost breakdown: what you will pay for
The build is the biggest cost, but it is not the only one. A two storey extension is a more involved project than a single storey one, so fees are higher and almost always include a full planning application.
| Cost item | Typical cost | Notes |
|---|---|---|
| Build (shell, roof, windows, finishes) | £1,950 – £2,400 per m² | Standard finish, ex VAT, before regional adjustment |
| Architectural design | 4 – 7% of build cost | Planning and building regulations drawings |
| Structural engineer | £500 – £2,500 | Usually at the top of this range for two storeys, with steel beams and foundation design |
| Building control | £600 – £1,200 | Local authority or approved inspector |
| Householder planning application | £548 | England, from 1 April 2026; no VAT |
| Lawful development certificate (if PD) | £274 | Optional, but proves your rear extension is lawful |
| Party wall surveyor | £1,000 – £3,000 per neighbour | Common on semis and terraces |
| VAT | 20% | On build and fees if your contractors are VAT-registered |
| Contingency | 10% of total | For ground conditions, drains and design changes |
For a 40m² standard extension in the Midlands, fees for design, engineer and building control come to about £4,000–£10,500, and VAT adds roughly £16,000–£21,000. Adding a 10% contingency takes the recommended budget to around £107,000–£138,500.
Real example: two storey rear extension on a 1930s semi in the South East
Project: 4m × 5m footprint on two floors (40m² total), open-plan kitchen-diner below and a double bedroom with en-suite above, standard finish
Region: South East
Approvals: householder planning application (£548) and a party wall agreement with one neighbour
- Build cost (ex VAT): £87,500 – £107,500
- Design, structural engineer and building control: £4,500 – £11,000
- Party wall surveyor: £1,000 – £3,000
- VAT at 20%: £18,500 – £24,500
- Total: about £112,000 – £146,500, or £123,500 – £161,500 with a 10% contingency
This is a modelled example from our calculator, not a quote. Kitchen units are not included – a mid-range kitchen would add £15,000–£30,000 plus VAT.
What affects the cost of a double storey extension?
Roof design
A pitched roof that ties neatly into the existing roof is usually cheapest in the long run and is what planners tend to prefer. Hipped roofs, valleys and complex junctions with the main roof add carpentry and tiling time.
Steelwork and open-plan layouts
Knocking the rear wall out to create one big kitchen-diner means steel beams to carry the first floor and roof above. BestBuilders puts steelwork at £3,000–£9,000 supplied and fitted for a two storey extension.
Foundations and ground conditions
Two storeys put more load on the ground, so foundations are deeper and wider. Clay soil, nearby trees and drains under the footprint can add £5,000–£15,000 (BestBuilders). A build-over agreement with your water company may also be needed.
Glazing
Large bi-fold or sliding doors cost £2,500–£9,000 per opening (BestBuilders). Upstairs windows are cheaper but must meet building regulations for escape and, on side elevations, may need to be obscure-glazed.
Scaffolding and access
Unlike most single storey projects, two storey extensions need full scaffolding for weeks or months. Poor rear access – common on terraces – means more labour carrying materials through the house.
Location
As the regional table shows, the same extension can cost around 35% more in London than in the North of England or Wales.
Two storey extension planning permission
Most two storey extensions in England need a householder planning application (£548 from April 2026). There are two key rules to know:
- Two storey side extensions always need planning permission. Permitted development only allows single storey side extensions.
- Two storey rear extensions can be permitted development if they extend no more than 3m beyond the original rear wall and are at least 7m from the rear boundary. The roof pitch must match the existing house as far as practicable, materials must be similar, upper-floor side windows must be obscure-glazed and non-opening below 1.7m, and eaves within 2m of a boundary cannot exceed 3m.
In practice, the 7m rear boundary rule rules out many terraced and semi-detached houses with short gardens. Permitted development does not apply to flats and maisonettes, and extensions of more than one storey to the rear are not permitted development on designated land (conservation areas, National Parks, National Landscapes and World Heritage Sites). Article 4 directions can also remove these rights. If you think your rear extension qualifies, a lawful development certificate (£274) gives you written proof.
Whatever the planning route, you will need building regulations approval, and the Party Wall etc. Act 1996 applies if you build on or near a shared wall or dig foundations close to a neighbour’s. Read our full guide to extension planning permission and permitted development.
How long does a two storey extension take?
- Design and structural drawings: 4–8 weeks
- Planning permission: the statutory target is 8 weeks from validation; allow 8–12 weeks in practice
- Party wall notices: at least one month (two months for work directly on a party wall), which can run alongside planning
- Tendering and builder availability: 1–3 months
- Build on site: roughly 14–22 weeks for a typical 30–40m² extension (BestBuilders)
From first sketches to moving in, most homeowners should expect 7–11 months.
Is it cheaper to build up or out?
Per square metre, building up is usually cheaper than building out. Our standard-finish rate for a double storey extension (£1,950–£2,400 per m²) is about 11–12% lower than for a single storey extension (£2,200–£2,700 per m²), because you are not paying for a second set of foundations and a second roof. If you would otherwise build a single storey extension now and add a floor later, doing both at once also avoids paying for scaffolding, design and approvals twice.
The cheapest way to build up, though, is often into the roof you already have. A dormer loft conversion typically costs £1,220–£1,740 per m² at a standard finish and does not use any garden. The trade-off is that a loft gives you bedroom space only, whereas a two storey extension can enlarge your living space downstairs as well. Compare the options in our guides to single storey extension costs and dormer loft conversion costs.
How to save money on a two storey extension
- Keep the footprint simple. A rectangular plan with a roof that ties into the existing one is far cheaper than a design with steps, hips and valleys.
- Line up the walls. Stacking the first-floor walls over the ground-floor walls reduces the steel needed.
- Check whether permitted development applies to a rear extension before designing something larger.
- Get ground investigations early. Trial holes cost little compared with redesigning foundations mid-build.
- Tender a full specification to at least three builders so quotes are like-for-like.
- Serve party wall notices early – a neighbour who consents in writing saves you surveyor fees.
- Do the decorating yourself and buy sanitaryware and flooring directly if your builder agrees.
Does a two storey extension add value?
Usually, yes – especially if it adds a bedroom. Nationwide’s research, reported in October 2025, found that an extension or loft conversion adding a double bedroom and bathroom can add up to 24% to the value of a three-bedroom, one-bathroom house, and that a 10% increase in floor space adds around 5% to a typical home’s price. Adding a double bedroom to a two-bedroom house added about 13%.
Whether that covers your costs depends on your house price. A 20% uplift on a £500,000 home in the South East is £100,000, close to the cost of the extension; the same percentage on a £200,000 home in the North is £40,000. Always check the ceiling price for your street before committing.
Frequently asked questions
How much does a 4m × 5m double storey extension cost?
A 4m × 5m footprint on two floors gives 40m² of floor area. At a standard finish that costs around £76,500–£94,000 to build (ex VAT) in the Midlands, or £97,500–£126,000 including design fees, planning and VAT. In London, budget around £123,500–£159,000.
How much does a two storey extension cost per m²?
Expect around £1,600–£1,950 per m² for a basic finish, £1,950–£2,400 standard and £2,400–£3,100 high-end, excluding VAT. Rates are per m² of total floor area across both storeys.
Is a two storey extension double the cost of a single storey?
No. A two storey extension usually costs around 1.7–1.8 times as much as a single storey extension with the same footprint, because the foundations and roof are shared. That is why its cost per m² is lower.
Can I build a two storey extension without planning permission?
Only to the rear, and only if it extends no more than 3m from the original rear wall, is at least 7m from the rear boundary and meets the other permitted development conditions. Two storey side extensions always need planning permission.
Is £100,000 enough for a two storey extension?
Outside London, £100,000 including VAT and fees typically covers a standard 30–40m² double storey extension, but not usually a new kitchen or a contingency. In London, £100,000 is more realistic for around 30m².
How long does a double storey extension take to build?
Most take around 14–22 weeks on site. Including design, planning and finding a builder, allow 7–11 months from start to finish.
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Sources and methodology
- Homebuilding & Renovating, How much does an extension cost in 2026? (updated 19 February 2026).
- BestBuilders, Average Cost of a Two-Storey Extension in 2026 UK (updated 22 August 2026).
- MyBuilder, Double Storey Extension Cost Guide (updated 25 November 2025).
- MyJobQuote, Double Storey Extension Cost Guide (UK Prices 2026) (updated 1 October 2026) and Side Extension Cost 2026 (updated 22 September 2026).
- HomeOwners Alliance, House Extension Costs: Breakdown by Size & Type (updated 30 July 2026).
- Federation of Master Builders, Two-storey extension costs (January 2026).
- Estate Agent Today, Price data shows why some owners choose to improve, not move – Nationwide research (15 October 2025).
- National planning application fees for England from 1 April 2026; Town and Country Planning (General Permitted Development) (England) Order 2015, Schedule 2, Part 1, Class A.
- How we calculate our cost estimates
All prices are guide figures for 2026 and vary with your property, specification, ground conditions and location. Always get detailed written quotes before starting work.
