What is a double-storey extension?
A double-storey extension (also called a two-storey extension) adds rooms on both the ground and first floor in one build. It typically gives a larger kitchen or living space downstairs and an extra bedroom or bathroom above.
The foundations and roof are shared between both floors, so the cost per square metre is usually lower than a single-storey extension. Most double-storey extensions need planning permission because of their height and closeness to neighbours.
What we handle
- Design drawings and planning application
- Structural engineer’s calculations
- Foundations, drainage and scaffolding
- Brick or block walls, floors and a roof tied into the house
- Windows, doors and staircase alterations
- Opening up at both levels with steel beams
- Electrics, heating, plumbing and plastering
- Building control sign-off
Options to consider
Rear or side
A rear extension suits deep gardens; a side extension uses the gap beside a semi or detached house.
Matching or contrasting finish
Matching brick and roof tiles keeps the house looking original. Render or cladding can give a modern look.
Bedroom with en-suite
The first floor often becomes a main bedroom with an en-suite, freeing up a smaller room elsewhere.
Hipped or gable roof
The roof is designed to tie into the existing one so the house still looks balanced.
How much does a double-storey extension cost?
A double-storey extension typically costs £1,650–£2,500 per m² of floor area (both floors) across the UK, including VAT at 20% (standard rate). A typical 36 m² project comes to roughly £59,500–£90,000. Build time is usually 14 to 20 weeks on site, after planning and building control approval. Design, structural calculations and council fees are extra.
| Region | Guide range (per m² of floor area (both floors)) |
|---|---|
| London | £2,150–£3,250 |
| South East | £1,850–£2,800 |
| East of England | £1,750–£2,650 |
| South West | £1,700–£2,550 |
| West Midlands | £1,600–£2,400 |
| East Midlands | £1,550–£2,400 |
| North West | £1,550–£2,350 |
| Yorkshire and the Humber | £1,550–£2,300 |
| North East | £1,500–£2,250 |
| Wales | £1,500–£2,300 |
| Scotland | £1,600–£2,400 |
| Northern Ireland | £1,400–£2,150 |
What changes the price:
- Total floor area across both floors
- Roof design and how it joins the existing roof
- Bathrooms or en-suites on the first floor
- Scaffolding and access to the rear
- Brick matching and external finishes
- Steel beams where walls are opened up
Use the guide price tool for a figure based on your measurements, or see all guide prices.
Do I need planning permission?
England
In England an extension of more than one storey can only be permitted development at the rear, no more than 3 metres deep and at least 7 metres from the rear boundary, with matching materials and any upper side windows obscure-glazed. Most double-storey extensions therefore go through a householder planning application.
Wales
In Wales a rear extension of more than one storey can be permitted development if the ground floor projects no more than 4 metres and the upper floor no more than 3 metres, with at least 10.5 metres to the rear boundary and obscure-glazed upper side windows. It is not permitted development in conservation areas, National Parks or National Landscapes, so many double-storey extensions need a householder application.
Scotland
In Scotland an extension of more than one storey is only permitted development if it is at least 10 metres from every boundary and no higher than the existing ridge, so most need planning permission. A building warrant is needed before work starts.
Northern Ireland
In Northern Ireland an extension of more than one storey can be permitted development at the rear if it projects no more than 3 metres and is at least 7 metres from the rear boundary. Two-storey side extensions, and any in a conservation area, need planning permission.
Even when planning permission is not needed, building regulations approval (a building warrant in Scotland) usually is. We make the applications and book the inspections.
How long does it take?
Typically 14 to 20 weeks on site, after planning and building control approval. Surveys, design and approvals usually take 3 to 4 months beforehand.
How it works
- 01
Free visit
We look at the property, discuss what you want and measure up.
- 02
Design and fixed quote
Drawings, calculations and an itemised price for the agreed specification.
- 03
Approvals
Planning or permitted development, building regulations and neighbour matters.
- 04
Build and sign-off
Built to a written programme, with a completion certificate at the end.
Double-storey extensions: questions and answers
Does a double-storey extension need planning permission?
Usually. In England a two-storey rear extension can only be permitted development if it is no more than 3 metres deep and at least 7 metres from the rear boundary, and side extensions over one storey always need permission. In practice most are approved through a planning application.
Is a double-storey extension cheaper per square metre?
Usually yes. You pay for one set of foundations and one roof but get two floors of space, so the cost per square metre is often lower than a single-storey extension.
Will the first floor need a new staircase?
Not normally. The new rooms are reached from the existing landing, though a doorway or short corridor may need to be formed.
How close can it be to my neighbour?
Councils look at loss of light and outlook for neighbours. Many apply a 45-degree guideline from the nearest neighbouring window. We design to the council’s published guidance to give the application the best chance.
Can I live at home during the work?
Most families stay put. The shell is built first and the house is opened up late in the job, so disruption inside is limited to a few weeks.
What drawings do I need?
Planning drawings for the application, then more detailed building regulations drawings and structural calculations for building control. We prepare both.