House extensions in Harrow
Every type of house extension in Harrow, from single-storey kitchen extensions to two-storey additions, side returns and orangeries. We design, handle the approvals and build.
- Postcode districtsHA0, HA1, HA2, HA3, HA7, HA9
- Price regionLondon (×1.3)
- Planning rulesEngland
- Site visitFree, no obligation
Guide prices for Harrow
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 |
| Side return extensions | 11 m² | £34,000 – £43,000 |
| Extensions over a garage | 12 m² | £32,500 – £42,500 |
| Double-storey extensions | 32 m² | £74,500 – £98,000 |
| Orangery extensions | 16 m² | £58,000 – £73,000 |
Areas we cover around Harrow
Site visits are available across Harrow (HA0, HA1, HA2, HA3, HA7, HA9). The same team covers Wealdstone (1 mile), Wembley (2 miles), Pinner (2 miles), Northolt (3 miles), Greenford (4 miles), all within easy reach. Bushey, in Hertfordshire, is roughly 5 miles from Harrow and also on our list.
Which extension suits a Harrow home?
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.
Start by comparing kitchen extensions, wraparound extensions and side return extensions: between them they cover most of the layouts we see requested for houses like these.
Planning and building control in Harrow
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).
Choose an extension type
- Bungalow extensions · from £34,000
- Side return extensions · from £23,000
- Building regulations for extensions · from £1,150
- Pitched roof extensions · from £28,500
- Glass box extensions · from £39,000
- Extension plans and drawings · from £1,550
- Kitchen extensions · from £35,000
- Flat roof extensions · from £27,000
- Single-storey rear extensions · from £27,000
- Utility and boot room extensions · from £18,000
- Orangery extensions · from £39,000
- Timber frame extensions · from £27,000
- Annexe extensions · from £71,500
- Conservatory replacement extensions · from £26,000
- Double-storey extensions · from £49,000
- Wraparound extensions · from £46,500
- Home office extensions · from £20,500
- Planning permission for extensions · from £450
- Extensions over a garage · from £31,000
- Bedroom extensions · from £33,500
- Side extensions · from £28,500
- Porch extensions · from £5,200
Free site visit
We visit your Harrow home, measure up, talk through what you want and check the planning position.
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
The price is fixed in writing once the design is settled, with a clear programme and payment stages.
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 Harrow
How much does an extension cost in Harrow?
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 cover all of Harrow?
Yes, including the surrounding parts of Greater London. Site visits are free and there is no obligation.
Do I need planning permission for an extension in Harrow?
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 Harrow, and the guide-price tool gives a range for your own size and finish in about a minute.
How long does an extension take in Harrow?
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 Harrow
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.