A single-storey extension is a new ground-floor room built onto your house, usually at the rear or side, with its own foundations, walls and roof, creating a bigger kitchen, living space or bedroom without moving home.
We build single-storey rear, side-return and wrap-around extensions for houses across the UK. Our free site survey and written quote looks at your plans or ideas, the ground and drainage, the wall the extension will join, and access for materials. We can work from your architect's drawings or arrange drawings, structural calculations and building control for you. Extensions suit growing families, people who want an open-plan kitchen and dining room, and anyone who would rather improve than move. We manage the build from foundations to plastering, coordinating every trade, and keep you updated at each stage so you know what is happening and when.
What’s included?
- Groundworks, foundations and below-ground drainage
- Cavity walls built and insulated to building regulations
- Flat or pitched roof, with rooflights or a lantern if specified
- Steel beams to open into the existing house
- Electrics and plumbing by qualified trades, with certificates
- Windows and external doors, including bifolds if chosen
- Plastering, screed floor and internal doors
- Building control inspections and completion certificate
Which options can you choose from?
How much does a single-storey extension cost?
Most jobs fall between £35,000–£75,000 for a typical 15–25m² rear extension, ready for kitchen and decoration, 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 extension (8–12m²) | A modest rear or side extension, such as a utility room or a slightly larger kitchen. | £22,000–£40,000 |
| Typical rear extension (15–25m²) | A kitchen-diner or family room with bifold doors and a rooflight or lantern. | £35,000–£75,000 |
| Large or wrap-around (30m² plus) | A wrap-around or wide rear extension, often with structural steelwork into the house. | £70,000–£130,000 |
What affects the price?
- Floor area, shape and number of corners
- Roof type, rooflights, lanterns and the amount of glazing
- Ground conditions, foundation depth and drains to divert
- Steelwork needed to open into the existing house
- Finishes, kitchen, flooring and heating specification
How do prices vary across the UK?
| Region | Guide price |
|---|---|
| London | £45,500–£98,000 |
| The South East | £39,000–£84,000 |
| The East of England | £37,000–£79,000 |
| The South West | £35,500–£76,000 |
| The West Midlands | £34,500–£74,000 |
| The East Midlands | £33,500–£72,000 |
| The North West | £33,000–£71,000 |
| Yorkshire and the Humber | £33,000–£70,000 |
| The North East | £31,500–£68,000 |
| Wales | £32,000–£69,000 |
| Scotland | £33,500–£72,000 |
| Northern Ireland | £30,000–£64,000 |
Regional figures apply typical labour and material cost differences to the national guide. They are not quotes.
Do you need planning permission for a single-storey extension?
Building regulations approval is needed for an extension anywhere in the UK, covering foundations, structure, insulation, drainage, ventilation and fire safety. In Scotland a building warrant is normally needed before work starts.
England
In England, many single-storey rear extensions are permitted development: typically up to 3 m deep on a semi-detached or terraced house and 4 m on a detached house, no more than 4 m high, and covering no more than half the land around the original house. Larger rear extensions can go through the prior approval process. Side extensions, flats, listed buildings, conservation areas and homes where permitted development rights have been removed need planning permission.
Building Regulations approval is needed for almost every extension, covering foundations, structure, insulation, drainage, ventilation and fire safety. If the work is on or near a shared wall or boundary, the Party Wall etc. Act 1996 may apply.
Wales
In Wales, permitted development allows many single-storey rear extensions, with depth and height limits that depend on the type of house and how close the extension comes to your boundaries. Side extensions, listed buildings, conservation areas and flats usually need planning permission.
Building Regulations in Wales apply to extensions, from foundations to insulation and fire safety. The Party Wall etc. Act 1996 applies in Wales as it does in England.
Scotland
In Scotland, Class 1A permitted development covers some single-storey extensions, within limits on depth, height and distance from boundaries, and not in conservation areas or on flats. Anything outside those limits needs planning permission from the council.
A building warrant from the council’s building standards service is usually needed before work starts, and a completion certificate is accepted at the end. There is no Party Wall Act in Scotland; work near a boundary is agreed with neighbours under general law.
Northern Ireland
In Northern Ireland, permitted development allows many single-storey rear extensions, typically up to 3 m deep on attached houses and 4 m on detached houses, within height and garden-coverage limits. Conservation areas, listed buildings and side extensions are more restricted.
Building control approval under the Building Regulations (Northern Ireland) is needed for extensions. Northern Ireland has no Party Wall Act, so boundary work is agreed with neighbours directly.
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: 10–16 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.
Single-storey extensions: frequently asked questions
How much does a single-storey extension cost?
A typical single-storey rear extension of 15–25m² costs £35,000–£75,000, built to a plastered finish ready for your kitchen and decoration. As a guide, allow roughly £1,600–£2,800 per square metre plus fixed costs for groundworks, steelwork and fees. Smaller extensions cost more per square metre. The kitchen, flooring and large glazed doors are usually the biggest extras. We confirm a fixed price for the agreed specification after the survey.
Do I need planning permission for a single-storey extension?
Whether you need planning permission depends on the extension's size and height, how close it is to boundaries, your home's location, whether it is listed or in a conservation area, and which UK nation you live in. In England, many rear extensions up to 3m deep on a semi or terrace, or 4m on a detached house, can be built under permitted development. We check the rules that apply to your home before quoting.
How long does a single-storey extension take to build?
A single-storey extension usually takes 10–16 weeks on site, from digging foundations to final plastering. Bad weather, deep foundations or a complex roof can add time. Before work starts, allow several weeks for drawings, structural calculations and building control approval, and longer if planning permission is needed. We give you a stage-by-stage programme with your quote so you know what happens each week.
Can we stay at home during the build?
Most people stay at home while we build a single-storey extension, because the new structure goes up outside before we break through. The disruptive part is usually the last few weeks, when we open into the house and fit the kitchen. We put up dust screens, keep a safe route through the house and agree a temporary kitchen setup if needed. Water and power are only off for short, planned periods.
What is the Party Wall Act and does it apply to me?
The Party Wall etc. Act 1996 applies in England and Wales only. In England and Wales, it requires you to give notice to neighbours before certain work on or near a shared wall, such as digging foundations within 3m of their building and deeper than its footings. Neighbours can agree or appoint a surveyor. Scotland and Northern Ireland have no equivalent Act, though general rights still apply. We identify whether notices are needed during the survey.
Is a flat roof or a pitched roof better on an extension?
A flat roof is quicker to build and usually costs less, gives a clean modern look and works well with a roof lantern. A pitched roof matches the main house, sheds water faster and allows a vaulted ceiling, but it costs more and its height can affect neighbours. Modern flat roofs in EPDM rubber or GRP last well when properly detailed. Planning rules on height can also decide the choice.
Do I need an architect for an extension?
You need proper drawings for an extension, but not always a full architect service. A designer or architectural technician can produce planning and building regulations drawings, and a structural engineer provides beam and foundation calculations. If you already have drawings, we price from them. If not, we can arrange the drawings and calculations as part of the project so everything is coordinated from the start.
What does a typical extension build look like week by week?
A typical single-storey extension follows the same order: clearing the site and digging foundations, building walls up to roof level, then fitting the roof and windows to make it weathertight. Electrics, plumbing, insulation and plastering follow. The last stage is opening into the house, laying the screed and fitting doors and finishes. Building control inspects at key stages, and we book those visits for you.