What is a single-storey extension?
A single-storey extension is a ground-floor addition, usually at the rear of a house, that enlarges a kitchen, living or dining space. Most are built with cavity walls on concrete foundations and finished with a flat roof and roof lantern or a pitched tiled roof.
How much does a single-storey extension cost in Southgate?
In Southgate, a single-storey extension typically costs £2,550–£3,750 per m² of floor area, including VAT at 20% (standard rate). For a typical 20 m² project that is roughly £51,000–£75,000. That range is adjusted for London, where domestic building work typically costs around 30% above the national average. Design, structural calculations and council fees are extra.
| Size or type | Guide range |
|---|---|
| Smaller project (14 m²) | £35,500–£52,500 |
| Typical project (20 m²) | £51,000–£75,000 |
| Larger project (28 m²) | £71,500–£105,000 |
| Rate per m² | £2,550–£3,750 |
The main things that change the cost:
- Glazing: sliding and bifold doors cost more than French doors
- How much of the existing house is opened up
- Roof type and the size of any lantern or roof windows
- Floor area and the length of new wall
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 single-storey extension in Southgate?
The approval route for Southgate is set by planning law in England. In England a single-storey rear extension is often permitted development: broadly up to 3 metres deep on a semi-detached or terraced house and 4 metres on a detached house, no higher than 4 metres, with eaves no higher than 3 metres within 2 metres of a boundary, and covering no more than half the garden. The larger home extension scheme allows up to 6 or 8 metres if you notify the council first and neighbours have a chance to comment. In conservation areas, National Parks and National Landscapes the larger home extension route, side extensions and cladding are not permitted development. Flats and houses whose rights have been removed need a planning application, and listed buildings need listed building consent.
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.
At the survey we check your house’s planning history and any restrictions, and tell you which route applies.
What we handle
The work we manage on a single-storey extension:
- Knock-through to the existing house with steel beams
- Structural calculations for steels and lintels
- Foundations, drainage and any build-over agreement
- First and second fix electrics, heating and plastering
- Measured survey and design drawings
- Cavity walls, insulation and roof to current building regulations
How long does it take?
Expect 10 to 14 weeks on site for a typical rear extension, after approvals. Before that, surveys, drawings and approvals usually take 6 to 12 weeks, longer if the council asks for changes.
Building in Southgate
Victorian and Edwardian terraces dominate many London streets, which is why side return, wraparound and mansard projects are so common here.
Projects in Southgate (N14 and N21) are surveyed in person before we quote, so the price reflects your actual property.
How it works
- 01
Visit and measured survey
A free visit to understand the project, check access and take measurements.
- 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 single-storey extensions in Southgate
Can I stay in the house during the build?
Usually yes. We build the shell before opening up the back wall, so the house stays weathertight for most of the job. There will be a few weeks when the kitchen or back room is out of use.
Do you build single-storey extensions in Southgate?
Yes. We build single-storey extensions across Southgate, including postcodes N14 and N21. Every project starts with a free home visit.
How much does a single-storey extension cost in Southgate?
In Southgate, a single-storey extension typically costs £2,550–£3,750 per m² of floor area, including VAT at 20% (standard rate). A typical 20 m² project comes to roughly £51,000–£75,000. Your fixed price depends on the survey and drawings.
Do I need planning permission for a single-storey extension?
Not always. Many small rear extensions are permitted development, within limits on depth, height and how much of the garden is covered. The limits depend on which nation you live in and on protected areas such as conservation areas, and flats or houses whose rights have been removed need an application. We check this at the survey and can apply to the council for formal confirmation.
How long does a single-storey extension take?
Once approvals are in place, a typical rear extension takes 10 to 14 weeks on site. Design and approvals usually take another 6 to 12 weeks beforehand, depending on whether a planning application is needed.