Double-storey extensions for homes in Harrow
Planning a double-storey extension in Harrow? We survey the house, work out the planning route, draw the design and build it, so you deal with one team from the first visit to the completion certificate.
- Guide price in HarrowFrom £49,000 inc VAT
- PlanningUsually a householder application
- Build time16–24 weeks on site
- Postcode districtsHA0, HA1, HA2, HA3, HA7
Working in Harrow
We cover Harrow and the postcode districts HA0, HA1, HA2, HA3, HA7, HA9. Nearby, we also take on projects in Wealdstone (1 mile), Wembley (2 miles), Pinner (2 miles), Northolt (3 miles).
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.
What should I budget for a double-storey extension in Harrow?
Labour and material costs vary across the UK, so for Harrow we use our London factor (×1.3). The ranges include VAT and exclude design, structural and council fees.
Typical rates in Harrow: £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 |
For a figure based on your own dimensions, use our guide-price tool.
Included in a typical project
- Ground and first floor structure, roof tied into the existing roof
- Householder planning application where needed
- Breaking through at both levels, stairs and landing changes where needed
- Insulation, plastering, electrics and plumbing to finish
- Building regulations drawings and structural design
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.
Planning and approvals in Harrow
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.
Homes in conservation areas, national parks, National Landscapes (formerly AONBs), the Broads and World Heritage Sites have tighter rules, so we always check the property's status and planning history before design starts.
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.
Applications are decided by the local planning authority (your district, borough or unitary council).
Our process, step by step
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
It starts with a visit to your house to measure, check access and talk through ideas and budget.
Design and approvals
We draw the design, agree it with you and handle planning or permitted development checks and building regulations.
Fixed written price
You receive a written, itemised price and programme. Nothing starts until you are happy with it.
Build and sign-off
Work is carried out to the agreed programme, inspected by building control and signed off at the end.
Double-storey extension questions answered
Will my neighbours in Harrow be involved?
If a planning application or prior approval is needed, the council notifies neighbours. If the work is on or near a shared boundary, party wall notices may also be needed.
Who do I contract with for a double-storey extension in Harrow?
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 Harrow?
On site, typically 16 to 24 weeks once approvals are in place. Before that, allow 8–16 weeks design and approvals.
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.
Does a double-storey extension need planning permission?
Often, yes. In England a two-storey rear extension can be permitted development only if it projects no more than 3 m and sits at least 7 m from the rear boundary, with matching roof pitch and obscure side windows. Side extensions over one storey always need planning permission. We confirm the route at the survey.
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.