Double-storey extensions in Harlesden: design, approvals and build
We design and build double-storey extensions for houses in Harlesden, with a written price once the survey and design are done and one point of contact throughout.
- Guide price in HarlesdenFrom £49,000 inc VAT
- PlanningUsually a householder application
- Build time16–24 weeks on site
- Postcode districtsNW10
What is included
- Insulation, plastering, electrics and plumbing to finish
- Measured survey, design and planning drawings
- Breaking through at both levels, stairs and landing changes where needed
- Householder planning application where needed
- Foundations sized for two floors
- Ground and first floor structure, roof tied into the existing roof
The roof is what makes a two-storey extension look right or wrong. We match the pitch and materials of the main house wherever possible and plan the upstairs layout around the existing landing so the new rooms feel original rather than bolted on.
Will the council need to approve it?
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.
Building over or within 3 m of a public sewer needs the water company's consent, usually through a build-over agreement, before the foundations go in.
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).
How much does a double-storey extension cost in Harlesden?
Prices below are for Harlesden, using the London factor of ×1.3. They are guide ranges including VAT for the build only, not a quote.
Typical rates in Harlesden: £2,020 to £3,900 per m² including VAT, depending on specification.
| Size | Essential | Standard | Premium |
|---|---|---|---|
| 3 m × 4 m, two floors 24 m² | £49,000 – £59,000 | £56,000 – £73,500 | £71,500 – £94,000 |
| 4 m × 4 m, two floors 32 m² | £64,000 – £77,000 | £74,500 – £98,000 | £95,500 – £125,000 |
| 4 m × 6 m, two floors 48 m² | £96,500 – £115,500 | £112,000 – £147,000 | £143,500 – £187,500 |
Want a range for your exact size? The guide-price tool takes about a minute.
Extensions in and around Harlesden
Across NW10, we can visit, measure and advise. The same team covers Willesden (1 mile), Cricklewood (2 miles), Wembley (2 miles), Acton (2 miles), all within easy reach.
Borehamwood, in Hertfordshire, is roughly 8 miles from Harlesden and also on our list. 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.
From first visit to completion
Site visits are free and there is no obligation. Where drawings are needed, the design stage is priced in writing before it starts.
Free site visit
First, a site visit: we look at the house, garden, access and drains and listen to what you need.
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
You receive a written, itemised price and programme. Nothing starts until you are happy with it.
Build and sign-off
Our team builds the extension, keeps you updated weekly and finishes with building control sign-off.
Your questions about a double-storey extension in Harlesden
Who do I contract with for a double-storey extension in Harlesden?
Your contract is with S&K Property Investments and Improvement Ltd, which designs and manages the project and the build teams who carry it out.
How long does a double-storey extension take to build in Harlesden?
On site, typically 16 to 24 weeks once approvals are in place. Before that, allow 8–16 weeks design and approvals.
Do I need building regulations approval in Harlesden?
Yes. Almost every extension needs it, whatever the planning route. We prepare the drawings and book the inspections.
Is a two-storey extension cheaper per square metre?
Usually. Our guide range is about £2,020 to £3,900 per m² of new floor area including VAT, compared with £2,280 to £4,420 per m² for single-storey work, because the foundations and roof are shared across two floors.
Do I need a Party Wall Agreement?
If you are in England or Wales and the work involves a shared wall or digging foundations close to a neighbour, the Party Wall etc. Act 1996 applies and notices must be served before work starts. We tell you which notices are needed.
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.