How much does a double storey extension cost in the UK?
For a standard double storey extension on a house with a good quality finish, most homeowners pay between £2,000 and £2,800 per square metre for the build itself in 2026. Because a two storey extension adds space on two floors from one set of foundations and one roof, the per square metre rate is often a little lower than a single storey build, even though the total is higher.
| Project | Total floor area (both floors) | Rough cost (build only, before VAT and fees) |
|---|---|---|
| Small double storey extension | around 24m² | £48,000 to £67,000 |
| Medium two storey extension | 30 to 40m² | £60,000 to £112,000 |
| Large double storey extension | 40m² and above | £80,000 to £150,000 |
These are build costs for a two storey extension. VAT, professional fees, planning, building control, scaffolding and any kitchen or bathroom fit out sit on top, and we cover those further down. Every site is different, so treat these as a starting budget and confirm with written quotes from local builders.
Double storey extension cost per m²
The clearest way to price a double storey extension is per square metre of total floor area, then adjust for finish and area. As a national guide for 2026, a two storey house extension costs £2,000 to £2,800 per m² for the build. That is usually 10 to 15 percent cheaper per square metre than an equivalent single storey extension, because the most expensive parts of any build, the foundations and the roof, are shared across two floors rather than one.
To use the rate, measure the rough length and width of the footprint, multiply them to get the area of one floor, then double it for a full two storey build. A 5m by 4m double storey extension gives 20m² per floor, so 40m² in total, which at £2,400 per m² works out at about £96,000 for the build. The calculator does this for you and adds the extras once you enter the total floor area across both floors.
Double storey extension cost by area of the UK
Location is one of the biggest factors in a double storey extension cost, so it pays to budget against your own area rather than a single national figure. As a guide for 2026:
| Area | Cost per m² (double storey) |
|---|---|
| North of England, including Manchester | £1,800 to £2,500 |
| Midlands | £2,000 to £2,700 |
| Scotland and Wales | £1,800 to £2,500 |
| London and the South East | £2,600 to £3,600 |
A double storey extension cost in London or the South East typically runs 20 to 40 percent above the national average, driven by higher labour rates and tighter access. A double storey extension cost in Manchester or elsewhere in the North, and in Scotland, tends to sit at the lower end. These are build rates only, before VAT and fees.
Cost per m² by finish: basic, standard and premium
Finish level is a major swing in the per m² price. As a rough guide for a double storey build in 2026:
| Finish level | Cost per m² | What it usually means |
|---|---|---|
| Basic | £1,900 to £2,200 | Blockwork, standard windows, painted plaster, simple layout |
| Standard | £2,100 to £2,600 | Upgraded glazing, good doors, underfloor heating downstairs, decent bathroom |
| Premium | £2,700 to £3,500 | Structural glazing, large span doors, high end finishes throughout both floors |
A basic double storey extension keeps costs down with a simple footprint and standard materials. A premium build costs more per m² but can add more value where it suits the house and the area.
Single storey vs double storey extension cost
A double storey extension is cheaper per square metre than a single storey one, but higher in total, because you are adding twice the floor area. Per m², building up is usually 10 to 15 percent better value, since the foundations and roof are shared. In total, though, a two storey extension costs more simply because there is more space, and it carries extras a single storey build does not, such as scaffolding and more structural steel.
If you only need ground floor space, a single storey build is the lower cost route. If you want both a bigger living area downstairs and an extra bedroom or bathroom upstairs, a double storey extension gives far better value for the money per square metre. You can compare the two directly using the single storey extension cost calculator.
What affects the cost of a double storey extension
Two double storey extensions of the same size can come back with very different quotes. The main things that move the price are:
| Cost driver | Effect on price |
|---|---|
| Size in m² | The single biggest factor. More total floor area means a higher overall cost, though the price per m² often eases as the project grows. |
| Finish and specification | A basic build sits far below a premium build with bi-fold doors, underfloor heating and a fitted kitchen and bathroom. |
| Extension position | A rear extension is the most straightforward. Side and wrap around builds carry more work tying the new roof and walls into the existing house. |
| Area of the UK | London and the South East run 20 to 40 percent above the national average. |
| Scaffolding | A two storey build needs full height scaffolding for the duration, which a single storey build often avoids. |
| Structural work and steel | Larger openings and load paths across two floors usually mean more steel and engineering. |
| Roof changes | Tying a new two storey roof into the existing roofline adds cost and complexity. |
| Staircase or landing changes | Reaching the new upstairs space can mean altering the existing landing or stairs. |
| Kitchen or bathroom fit out | A new kitchen can add £15,000 to £35,000, and an upstairs bathroom several thousand more. |
| Ground and access conditions | Poor soil, sloping plots or tight access push up groundwork and labour. |
Labour usually accounts for around 35 to 50 percent of the total. Scaffolding and structural work weigh more heavily on a double storey extension than on a single storey one, which is part of why the total is higher even when the per m² rate is lower.
Double storey extension cost by type
Double storey rear extension cost
A double storey rear extension, sometimes searched as a two storey rear extension, is the most common two storey build. It extends off the back of the house on both floors, typically adding a larger kitchen or living space downstairs and a bedroom or bathroom upstairs. It follows the standard £2,000 to £2,800 per m² range. A 40m² double storey rear extension works out at roughly £80,000 to £112,000 for the build in most of the UK, and more in London. See our dedicated rear extension cost calculator to compare rear builds.
Double storey side extension cost
A double storey side extension, or two storey side extension, builds into the space at the side of the house across both floors. It is common on detached and semi detached homes with room to the side, and it can add a downstairs room plus an extra bedroom above. Cost sits within the standard per m² range, though matching the new roofline and walls to the existing house can add to the figure.
Double storey wrap around extension cost
A double storey wrap around extension combines a rear and a side extension across two floors, giving the largest amount of new space in a single project. Because it is bigger and more complex, it sits at the upper end of the per m² range, and the total is higher simply because of the larger footprint over both storeys. Budget from the standard rate and expect the overall figure to reflect the combined rear and side areas on each floor.
Small double storey extension cost
A small double storey extension in the UK, often around 12m² per floor for 24m² in total, starts from roughly £48,000 to £67,000 for the build before VAT and fees. A smaller two storey build can carry a higher per m² rate than a larger one, because the fixed costs of scaffolding, foundations and roof are spread over less floor area. That is worth keeping in mind if you are comparing a small project against a bigger one on a per m² basis.
Double storey extension cost by property type
The type of house affects a double storey extension cost:
- Terraced houses usually mean a rear extension only, with party wall agreements needed on both sides and tight access that can raise labour costs.
- Semi detached houses often suit a side or rear double storey extension, with a party wall agreement needed on the attached side.
- Detached houses give the most freedom for a side, rear or wrap around double storey extension, with easier access, though matching a larger roofline can add cost.
For a full breakdown by property type across all extension types, see the main house extension cost calculator homepage.
Extra costs to budget for
The per m² figure covers the build and basic finishes. These extras are usually separate:
- VAT. Most extension work is subject to VAT, so check with your builder how it applies to your quote.
- Planning permission. A full double storey extension usually needs planning permission rather than falling under permitted development. If you need a householder application in England, the fee is £548 from 1 April 2026. Scotland and Wales fees differ. Confirm the current figure on GOV.UK before you apply.
- Building regulations. Every two storey extension must meet building regs for structure, insulation, drainage and fire safety. Inspection fees vary by council, usually £500 to £1,200.
- Professional fees. Architect and structural engineer fees weigh more on a double storey build because of the extra structural design. Expect roughly 10 to 15 percent of the build cost.
- Party wall surveyor. If you build against or near a shared wall, a party wall agreement and surveyor may be required, more likely on terraced and semi detached homes.
- Scaffolding. Full height scaffolding is needed for the duration of a two storey build.
- Kitchen or bathroom fit out. A new kitchen can add £15,000 to £35,000, plus the cost of an upstairs bathroom.
- Contingency. Set aside 10 to 15 percent for surprises, especially in older houses.
Do I need planning permission for a double storey extension?
Usually, yes. Most full two storey house extensions need planning permission, because they exceed the limits that permitted development allows for size, height and how close they sit to boundaries. A double storey rear extension in particular tends to need an application, as the height and depth go beyond permitted development rules. If your home is in a conservation area or an Area of Outstanding Natural Beauty, or has Article 4 restrictions, the rules are tighter still. Always check with your local planning authority before you start.
Does a double storey extension add value?
A well designed double storey extension can add strong value, because it adds both living space downstairs and bedroom or bathroom space upstairs, which is exactly what many buyers look for. The return depends on your location, the finish and how well the new layout works with the rest of the house. An extension that adds a well proportioned bedroom and a bright family room tends to appeal, while one with an awkward layout or poor light works less well. As a rough guide, a good two storey extension in the right home can add in the region of 10 to 20 percent to the value, but the figure varies widely by area, so treat it as a bonus rather than a guaranteed return.
How the calculator works
The double storey house extension cost calculator turns the per m² method into a single figure for your project. You choose:
- Extension position, such as rear, side or wrap around.
- Total floor area across both floors in m², or use the length and width helper if you do not know your area.
- Finish level, from basic through standard to premium.
- Region, since area moves the figure by 20 to 40 percent.
It then shows a low to high total for the build across both floors, the per m² rate used, and a separate line for extras like planning and building control, so the estimate stays honest rather than hiding the add ons inside one number. Enter your details at the end to save your estimate and get a copy.
For other extension types, see the main house extension cost calculator homepage, or the single storey extension cost calculator if you are weighing up building out against building up.
Frequently asked questions
How much does a double storey extension cost per m2 in the UK?
Most double storey extensions cost £2,000 to £2,800 per m² for the build in 2026, higher in London and the South East. A 40m² two storey extension is roughly £80,000 to £112,000 before VAT and fees.
Is a double storey extension cheaper than two single storey extensions?
Per square metre, yes. Building up shares the foundations and roof across two floors, so a two storey extension is usually 10 to 15 percent cheaper per m² than adding the same floor area as two separate single storey builds.
Do I need planning permission for a double storey extension?
Usually. Most full two storey house extensions need planning permission rather than falling under permitted development, and conservation areas have tighter rules. Check with your local planning authority before starting.
Does a double storey extension need deeper foundations?
It can. A two storey extension carries more load than a single storey one, so the foundations are often designed to suit, which is confirmed by a structural engineer and building control.
Does the estimate include VAT?
The per m² figures usually exclude VAT and fit out. The calculator shows extras separately, and you should ask your builder to confirm how VAT applies to your project.
How long does a double storey extension take to build?
Most double storey extensions take around 16 to 26 weeks on site, depending on size, finish and access. A straightforward rear build is quicker, while a large wrap around with roof changes takes longer.
Figures on this page are current UK market ranges for 2026 and are intended as a budgeting guide. Prices vary by area, specification and site conditions. Planning and building control fees are official figures that should be confirmed on GOV.UK and with your local council before you apply.