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.
How much does a double-storey extension cost in Greater London?
In Greater London, a double-storey extension typically costs £2,150–£3,250 per m² of floor area (both floors), including VAT at 20% (standard rate). For a typical 36 m² project that is roughly £77,500–£117,000. The guide for Greater London reflects typical costs in London, roughly 30% above the UK-wide figure. Design, structural calculations and council fees are extra.
| Size or type | Guide range |
|---|---|
| Smaller project (25 m²) | £54,000–£81,000 |
| Typical project (36 m²) | £77,500–£117,000 |
| Larger project (50 m²) | £107,500–£162,500 |
| Rate per m² | £2,150–£3,250 |
Your quote will depend mainly on:
- Bathrooms or en-suites on the first floor
- Roof design and how it joins the existing roof
- Total floor area across both floors
- Steel beams where walls are opened up
Your exact price depends on the survey and drawings. The guide price tool gives a quick range in the meantime.
Do you need planning permission for a double-storey extension in Greater London?
The approval route for Greater London is set by planning law in 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.
Building regulations approval comes from the council’s building control service or a registered building control approver. The work is inspected at key stages, such as foundations, drainage and insulation, and a completion certificate is issued at the end.
We check this for your address before design work starts, so there are no surprises later.
What we handle
Handled as part of most double-storey extensions:
- Building control sign-off
- 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
- Structural engineer’s calculations
- Foundations, drainage and scaffolding
How long does it take?
Expect 14 to 20 weeks on site, after planning and building control approval. Before that, surveys, drawings and approvals usually take 3 to 4 months, longer if the council asks for changes.
Building in Greater London
Space is at a premium in London, so homeowners often build out into the side return or up into the roof rather than move.
Places we cover in Greater London include Acton, Balham, Barking, Barnes, Barnet and Battersea.
How it works
- 01
Visit and measured survey
A free visit to understand the project, check access and take measurements.
- 02
Design and pricing
Design options, then a fixed quote based on the chosen drawings and specification.
- 03
Approvals in place
We handle planning, building control and neighbour notices before work starts.
- 04
Build and sign-off
We run the build to a written programme and hand over the completion certificate.
Questions about double-storey extensions in Greater London
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.
How much does a double-storey extension cost in Greater London?
In Greater London, a double-storey extension typically costs £2,150–£3,250 per m² of floor area (both floors), including VAT at 20% (standard rate). A typical 36 m² project comes to roughly £77,500–£117,000. Your fixed price depends on the survey and drawings.
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.
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.
How long does a double-storey extension take in Greater London?
Typically 14 to 20 weeks on site, after planning and building control approval. Design and approvals beforehand usually take 3 to 4 months.