A double-storey extension adds two floors of new space to your house in one build, typically a larger kitchen or living room downstairs with an extra bedroom, bathroom or en-suite above, sharing one set of foundations and one roof.
We build two-storey rear and side extensions that add space on both floors for less per square metre than two separate projects. Our free site survey and written quote covers the ground and drainage, how the new roof will join the existing one, the position of stairs and landings, and access for scaffolding and deliveries. We can price from your drawings or arrange drawings, structural calculations and building control. Double-storey extensions suit families who need another bedroom and a bigger kitchen at the same time. We manage the whole build, from foundations and brickwork to roofing, first-floor joists, plastering and finishes, coordinating every trade and keeping you informed at each stage.
What’s included?
- Groundworks, foundations and below-ground drainage
- Insulated cavity walls with brick or render to match the house
- First-floor joists, stud walls and new openings upstairs
- Roof structure tied into the existing roof, tiled to match
- Scaffolding for the full build, erected and inspected
- Electrics, plumbing and heating by qualified trades, with certificates
- Windows, external doors, plastering and internal doors
- Building control inspections and completion certificate
Which options can you choose from?
How much does a double-storey extension cost?
Most jobs fall between £60,000–£120,000 for a typical 30–40m² two-storey extension, both floors combined, including VAT at 20%. The table shows three typical levels of work; the figures are national guides, confirmed in writing after a free site survey.
| Type of job | What it usually involves | Guide price |
|---|---|---|
| Small (15–20m² total) | A compact rear or side extension adding a small room on each floor. | £40,000–£65,000 |
| Typical (30–40m² total) | A larger kitchen or living room below with a double bedroom or en-suite above. | £60,000–£120,000 |
| Large (50m² plus total) | Wide or deep extensions, often with a new bathroom, steelwork and high-spec glazing. | £100,000–£180,000 |
What affects the price?
- Combined floor area across both storeys
- How the new roof joins the existing roof
- Bathrooms, en-suites and plumbing on the upper floor
- Foundation depth, ground conditions and drains to divert
- Scaffolding duration, access and the level of finishes
How do prices vary across the UK?
| Region | Guide price |
|---|---|
| London | £78,000–£156,000 |
| The South East | £67,000–£134,000 |
| The East of England | £63,000–£126,000 |
| The South West | £61,000–£122,000 |
| The West Midlands | £59,000–£118,000 |
| The East Midlands | £58,000–£115,000 |
| The North West | £57,000–£114,000 |
| Yorkshire and the Humber | £56,000–£113,000 |
| The North East | £54,000–£108,000 |
| Wales | £55,000–£110,000 |
| Scotland | £58,000–£115,000 |
| Northern Ireland | £52,000–£103,000 |
Regional figures apply typical labour and material cost differences to the national guide. They are not quotes.
Do you need planning permission for a double-storey extension?
Building regulations approval is needed for any two-storey extension in the UK, covering structure, fire escape from upper rooms, insulation, drainage and ventilation. In Scotland a building warrant is normally needed before work starts.
England
In England, a two-storey rear extension can only be permitted development if it is no more than 3 m deep, at least 7 m from the rear boundary and finished to match the house. Most double-storey and all two-storey side extensions need full planning permission.
Building Regulations approval is needed, with structural calculations for beams, foundations and the roof. The Party Wall etc. Act 1996 often applies on semi-detached and terraced houses.
Wales
In Wales, two-storey extensions are tightly limited under permitted development, including distance to the rear boundary, so most need planning permission.
Building Regulations approval is needed in Wales, and the Party Wall etc. Act 1996 applies to work on or near shared walls.
Scotland
In Scotland, extensions of more than one storey are only permitted development in narrow cases (Class 1B, well away from the boundary they face and outside conservation areas), so most need planning permission.
A building warrant is required before work starts. Scotland has no Party Wall Act; neighbour and title issues are handled under general law.
Northern Ireland
In Northern Ireland, two-storey extensions usually need planning permission from the council.
Building control approval is needed under the Building Regulations (Northern Ireland). There is no Party Wall Act in Northern Ireland.
Rules change and every property is different, so we check the planning history and constraints for your address before we quote.
How long does it take?
Typical time on site: 14–22 weeks on site. Lead times for materials, drawings and approvals come before that and are set out in your written quote.
How does the job run?
Free site survey
We visit, measure up, look at access and the condition of what’s there, and talk through options and budget with you.
Written quote
You get a written quote with a fixed price for the agreed specification, what’s included, the payment stages and a likely start window.
Plan and prepare
We sort drawings, approvals and materials, agree dates with you and explain what to expect each week before work starts.
Build and hand over
The work is carried out, checked and cleared away. We walk round it with you and pass on certificates and product details.
Double-storey extensions: frequently asked questions
How much does a double-storey extension cost?
A typical double-storey extension of 30–40m² across both floors costs £60,000–£120,000, built to a plastered finish. As a rough guide, allow around £1,400–£2,600 per square metre plus fixed costs for groundworks, scaffolding and fees. The second storey usually costs less per square metre than the first, because foundations and roof are shared. Bathrooms upstairs and a complex roof add most. We confirm a fixed price after the survey.
Do I need planning permission for a two-storey extension?
Most two-storey extensions need planning permission, but it depends on the size, height and position, your home's location, whether it is listed or in a conservation area, and which UK nation you are in. In England, a two-storey rear extension can sometimes be built under permitted development if it is no deeper than 3m and at least 7m from the rear boundary. We check what applies before quoting.
Is a double-storey extension better value than single-storey?
A double-storey extension usually gives better value per square metre than a single-storey one, because the same foundations and roof serve twice the floor area. The overall cost is higher, and planning can be harder because of the effect on neighbours. If you might want an extra bedroom later, building both floors now avoids a second round of disruption and scaffolding.
How long does a double-storey extension take?
A double-storey extension typically takes 14–22 weeks on site, depending on size, roof design and weather. Foundations and ground-floor walls come first, then the first-floor joists, upper walls and roof. Once it is weathertight, electrics, plumbing, plastering and finishes follow. Allow extra time beforehand for drawings, calculations and approvals. We give you a stage-by-stage programme with your quote.
Can we live at home while it is built?
Most families stay at home during a double-storey extension. The new structure is built outside first, and we only break through into the existing rooms near the end, usually one floor at a time. Upstairs, this may mean a bedroom is out of use for a week or two. We fit dust screens, protect floors and stairs, and plan any time without water or power in advance.
How is the new roof joined to the existing house?
The new roof is usually tied into the existing roof so the two read as one. On a rear extension this often means a lower ridge or a hipped end, with valleys where the slopes meet. We strip back some existing tiles, fix new rafters and battens, and lay matching tiles or slates. Lead or proprietary flashings seal the junctions so water runs off properly.
Can the new upstairs room have its own bathroom?
A new upstairs room can usually have an en-suite, provided waste pipes can reach the soil stack or a new one can be installed. Running the waste pipe to the right falls is the main design question, and a pumped system is an option where gravity will not work. We plan bathroom positions at the design stage so pipes, ventilation and insulation are built in rather than added later.
Will the extension affect my neighbours?
A double-storey extension can affect neighbours' light, outlook and privacy, which is why planning departments look closely at height, depth and window positions. Side windows facing neighbours often need obscure glass. Work near a shared wall may also need party wall notices; the Party Wall etc. Act 1996 applies in England and Wales only. We talk through these points early so the design is realistic.