Extending your home in Harlesden
Planning an extension in Harlesden? Compare extension types, see guide prices adjusted for Harlesden and book a free site visit.
- Postcode districtsNW10
- Price regionLondon (×1.3)
- Planning rulesEngland
- Site visitFree, no obligation
Guide prices for Harlesden
Prices on this page use our London factor of ×1.3, include VAT at 20% and cover the build; your written price follows a survey and agreed drawings.
| Extension type | Example size | Standard spec (inc VAT) |
|---|---|---|
| Wraparound extensions | 25 m² | £74,500 – £94,500 |
| Single-storey rear extensions | 20 m² | £53,000 – £68,000 |
| Side return extensions | 11 m² | £34,000 – £43,000 |
| Extensions over a garage | 12 m² | £32,500 – £42,500 |
| Conservatory replacement extensions | 14 m² | £39,000 – £50,500 |
Covering Harlesden and nearby
Postcode districts we cover around Harlesden include NW10. We also work in nearby Willesden (1 mile), Cricklewood (2 miles), Wembley (2 miles), Acton (2 miles), Shepherds Bush (3 miles). Just over the Hertfordshire border, Borehamwood is about 8 miles away.
Do extensions in Harlesden need planning permission?
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 two-storey rear extension is permitted development only if it projects no more than 3 m from the original rear wall, sits at least 7 m from the rear boundary, matches the roof pitch and uses obscure, non-opening side windows upstairs. Most two-storey extensions therefore go through a householder planning application, which costs £548 from 1 April 2026 and normally takes about 8 weeks.
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.
If the work involves a shared wall, building on the boundary, or digging foundations within 3 m (sometimes 6 m) of a neighbour's building, the Party Wall etc. Act 1996 applies and notice must be served before work starts: two months for work to a party wall, one month for new walls on the boundary and for excavations.
Applications are decided by the local planning authority (your district, borough or unitary council).
Choosing the right extension in Harlesden
In London, space is at a premium and gardens are often short, so side returns, wraparounds and carefully planned rear extensions tend to make the most of every metre.
Start by comparing side return extensions, kitchen extensions and glass box extensions: between them they cover most of the layouts we see requested for houses like these.
Choose an extension type
- Glass box extensions · from £39,000
- Kitchen extensions · from £35,000
- Extension plans and drawings · from £1,550
- Building regulations for extensions · from £1,150
- Side return extensions · from £23,000
- Timber frame extensions · from £27,000
- Conservatory replacement extensions · from £26,000
- Double-storey extensions · from £49,000
- Flat roof extensions · from £27,000
- Pitched roof extensions · from £28,500
- Single-storey rear extensions · from £27,000
- Side extensions · from £28,500
- Extensions over a garage · from £31,000
- Orangery extensions · from £39,000
- Annexe extensions · from £71,500
- Wraparound extensions · from £46,500
- Porch extensions · from £5,200
- Home office extensions · from £20,500
- Bungalow extensions · from £34,000
- Bedroom extensions · from £33,500
- Utility and boot room extensions · from £18,000
- Planning permission for extensions · from £450
Free site visit
It starts with a visit to your house to measure, check access and talk through ideas and budget.
Design and approvals
Once the layout is agreed, we deal with the council: planning permission or written confirmation that none is needed, plus building control.
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 Harlesden
How much does an extension cost in Harlesden?
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 I need planning permission for an extension in Harlesden?
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.
Can I get a price before anyone visits?
Yes. This page shows guide prices adjusted for Harlesden, and the guide-price tool gives a range for your own size and finish in about a minute.
Do you handle building regulations?
Yes. We prepare the drawings and calculations, submit them and book inspections, ending with a completion certificate.
Will my neighbours need to be told?
If you apply for planning or prior approval the council notifies them, and in England party wall notices may be needed for work near a shared boundary.
Book a free site visit in Harlesden
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.