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 Islington?
In Islington, 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 Islington 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 |
Your quote will depend mainly on:
- Boundary walls and access for materials
- Single or two storeys
- Drains, gas meters or soil pipes that need moving
- Internal fit-out of the new rooms
A guide range is only a starting point: the guide price tool gives an instant figure for your size, and a free survey turns it into a fixed quote.
Do you need planning permission for a side extension in Islington?
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.
We check this for your address before design work starts, so there are no surprises later.
What we handle
What we take care of:
- Foundations and drainage alterations
- Opening into the existing house
- Survey of the boundary, drains and access
- Structural calculations
- Walls, roof and windows to match the house
- Building control completion
How long does it take?
Expect 10 to 16 weeks on site depending on size and storeys. Design and approvals come first and typically take 3 to 4 months, depending on the approval route.
Building in Islington
Space is at a premium in London, so homeowners often build out into the side return or up into the roof rather than move.
Projects in Islington (EC1P, EC4P, EC50 and N1) are surveyed in person before we quote, so the price reflects your actual property.
How it works
- 01
Survey and brief
We visit, discuss your ideas and budget, and survey the property or site at no cost.
- 02
Design and fixed quote
Drawings, structural calculations and an itemised, fixed price for the agreed specification.
- 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 Islington
Who approves a side extension in Islington?
Planning matters in Islington go to the council covering your address, and the work needs building control approval. We prepare and submit the applications for you.
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.
How close to the boundary can I build?
You can build up to the boundary, but the eaves height near it is limited under permitted development, and planning officers often want a gap at first floor. If you build on or near a shared boundary, party wall rules may apply.
How much does a side extension cost in Islington?
In Islington, 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.
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.