Extending your home in Barnet
Planning an extension in Barnet? Compare extension types, see guide prices adjusted for Barnet and book a free site visit.
- Postcode districtsEN4, EN5, N20
- Price regionLondon (×1.3)
- Planning rulesEngland
- Site visitFree, no obligation
Where we work near Barnet
Our survey diary covers Barnet, including EN4, EN5, N20. The same team covers East Barnet (2 miles), Friern Barnet (3 miles), Finchley (3 miles), Palmers Green (4 miles), Muswell Hill (5 miles), all within easy reach. For homes towards Hertfordshire, Potters Bar is around 3 miles away.
Choosing the right extension in Barnet
Across London, terraced houses with narrow side returns and tight access are the norm, which shapes everything from party wall notices to how materials reach the back garden.
For many houses here, side return extensions, wraparound extensions or glass box extensions gives the most useful space for the budget.
Guide prices for Barnet
We publish guide prices so you can budget before anyone visits. For Barnet they are adjusted by ×1.3, the factor we use across London.
| Extension type | Example size | Standard spec (inc VAT) |
|---|---|---|
| Single-storey rear extensions | 20 m² | £53,000 – £68,000 |
| Double-storey extensions | 32 m² | £74,500 – £98,000 |
| Side return extensions | 11 m² | £34,000 – £43,000 |
| Conservatory replacement extensions | 14 m² | £39,000 – £50,500 |
| Orangery extensions | 16 m² | £58,000 – £73,000 |
| Wraparound extensions | 25 m² | £74,500 – £94,500 |
| Extensions over a garage | 12 m² | £32,500 – £42,500 |
Approvals for an extension in Barnet
In England a single-storey rear extension can usually go up to 3 m beyond the original rear wall of a semi-detached or terraced house, or 4 m on a detached house, without a planning application, provided it is no more than 4 m high, keeps eaves to 3 m within 2 m of a boundary and, with other buildings, covers no more than half the land around the original house. The larger home extension prior approval scheme raises those depths to 6 m and 8 m, with neighbours notified and a 42-day decision.
In England a single-storey side return infill is often permitted development if it stays within the height limits and is no wider than half the width of the original house. Conservation areas, listed buildings and flats always need an application, and the boundary wall usually brings in the Party Wall Act.
In a conservation area, national park, National Landscape, the Broads or a World Heritage Site the permitted development limits are tighter (no side or two-storey extensions without an application). Listed homes need listed building consent, and if permitted development rights have been removed, any extension needs an application.
Building regulations approval is separate from planning. In England you can use the council's building control team or a registered building control approver; a full plans application gets the drawings checked before work starts, and the inspector signs the work off with a completion certificate.
Applications are decided by the local planning authority (your district, borough or unitary council).
Every extension type in Barnet
- Conservatory replacement extensions · from £26,000
- Building regulations for extensions · from £1,150
- Extension plans and drawings · from £1,550
- Side return extensions · from £23,000
- Wraparound extensions · from £46,500
- Glass box extensions · from £39,000
- Bungalow extensions · from £34,000
- Kitchen extensions · from £35,000
- Annexe extensions · from £71,500
- Pitched roof extensions · from £28,500
- Single-storey rear extensions · from £27,000
- Bedroom extensions · from £33,500
- Porch extensions · from £5,200
- Extensions over a garage · from £31,000
- Flat roof extensions · from £27,000
- Planning permission for extensions · from £450
- Side extensions · from £28,500
- Timber frame extensions · from £27,000
- Orangery extensions · from £39,000
- Double-storey extensions · from £49,000
- Home office extensions · from £20,500
- Utility and boot room extensions · from £18,000
Free site visit
A designer visits, takes measurements and photos, and discusses layouts, budget and timing with you.
Design and approvals
We produce the drawings and structural design, and manage the approvals so they are in place before work starts.
Fixed written price
We confirm the build price in writing, based on the approved drawings and the finishes you have chosen.
Build and sign-off
Work is carried out to the agreed programme, inspected by building control and signed off at the end.
Questions about extensions in Barnet
How much does an extension cost in Barnet?
Using our London factor (×1.3), a standard-spec single-storey extension of 20 m² is a guide £53,000 to £68,000 including VAT, and a 32 m² two-storey extension £74,500 to £98,000. Your written price follows the survey.
Do you handle building regulations?
Yes. We prepare the drawings and calculations, submit them and book inspections, ending with a completion certificate.
Do I need planning permission for an extension in Barnet?
Not always. It depends on the size, position and your property's history. Many single-storey rear extensions in England are permitted development or can use prior approval.
How long does an extension take in Barnet?
Usually 2 to 4 months of design and approvals, then 10 to 16 weeks on site for a single-storey extension or 16 to 24 weeks for two storeys.
Book a free site visit in Barnet
We will measure up, check the planning position and give you honest guide figures.
- Free, no-obligation site visit
- Planning route checked before you spend on drawings
- Written price once the design is agreed
- Building control sign-off at the end
Prefer to talk? Call 0800 088 6341 or .
Book a free site visit
Tell us a little about the project and we will arrange a time.