What is a side extension?
A side extension builds into the space beside a semi-detached or detached house, often over a driveway or side passage. It can be single-storey, for a utility room, downstairs toilet or study, or two-storey to add a bedroom above.
How much does a side extension cost in Twickenham?
In Twickenham, a side extension typically costs £2,200–£3,450 per m² of floor area, including VAT at 20% (standard rate). For a typical 28 m² project that is roughly £61,500–£96,500. The guide for Twickenham 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 (20 m²) | £44,000–£69,000 |
| Typical project (28 m²) | £61,500–£96,500 |
| Larger project (39 m²) | £86,000–£134,500 |
| Rate per m² | £2,200–£3,450 |
The main things that change the cost:
- Boundary walls and access for materials
- Internal fit-out of the new rooms
- Single or two storeys
- Drains, gas meters or soil pipes that need moving
For a figure based on your own measurements, try the guide price tool, then book a free home visit for a fixed quote.
Do you need planning permission for a side extension in Twickenham?
Here is how the rules work for a side extension in England. In England a single-storey side extension can be permitted development if it is no more than 4 metres high and no wider than half the width of the original house. Side extensions of more than one storey always need planning permission, as do side extensions in conservation areas, National Parks and National Landscapes.
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.
If the answer is not clear-cut, we can apply for formal confirmation before you commit to the build.
What we handle
Handled as part of most side extensions:
- Foundations and drainage alterations
- Building control completion
- Survey of the boundary, drains and access
- Electrics, heating and plastering
- Structural calculations
- Planning drawings and application
How long does it take?
The build itself usually takes 10 to 16 weeks on site depending on size and storeys. Allow time beforehand for drawings and approvals, usually 3 to 4 months.
Building in Twickenham
Many London boroughs have conservation areas and detailed design guides, so early design advice saves time at the planning stage.
Twickenham sits in Greater London, about 10 miles south-west of central London. We cover the whole of Twickenham, including postcodes TW1 and TW2.
How it works
- 01
Visit and measured survey
A free visit to understand the project, check access and take measurements.
- 02
Drawings and written quote
We prepare the design and give you a written, itemised quote with inclusions and exclusions.
- 03
Approvals
Planning or permitted development confirmation, building regulations and any party wall matters.
- 04
Build and sign-off
We run the build to a written programme and hand over the completion certificate.
Questions about side extensions in Twickenham
Can a side extension go over a drain?
Often yes, with a build-over agreement from the water company or by rerouting the drain. We check this during the survey.
Can I build a side extension without planning permission?
In England a single-storey side extension can be permitted development if it is no more than 4 metres high and no wider than half the original house, and the house is not in a conservation area or similar protected land. Two-storey side extensions always need planning permission.
How much does a side extension cost in Twickenham?
In Twickenham, a side extension typically costs £2,200–£3,450 per m² of floor area, including VAT at 20% (standard rate). A typical 28 m² project comes to roughly £61,500–£96,500. Your fixed price depends on the survey and drawings.
How long does a side extension take in Twickenham?
Typically 10 to 16 weeks on site depending on size and storeys. Design and approvals beforehand usually take 3 to 4 months.
Will I lose my driveway?
A side extension often takes the side drive. We look at whether parking can be kept at the front and whether a dropped kerb is needed.