A double-storey extension adds two floors of new space to your house in one build, typically a larger kitchen or living room downstairs with an extra bedroom, bathroom or en-suite above, sharing one set of foundations and one roof.
If you live in Hounslow and are weighing up a double-storey extension, the starting point is a visit to measure up and talk through what you want, which costs nothing. We cover homes across TW3, TW4, TW5 and TW7, and a typical project of this kind in London lands somewhere in the £78,000–£156,000 bracket, including VAT. The exact figure depends on size, access and the finish you choose.
- Guide price
- £78,000–£156,000 inc VAT
- Time on site
- 14–22 weeks on site
- Postcodes
- TW3, TW4, TW5, TW7 and TW8
- Planning rules
- England
- Local area
- Greater London
- Survey
- Free, with a written quote
Double-storey extensions prices in Hounslow
The costs listed here are typical for a double-storey extension around Hounslow and include VAT. They reflect labour and material costs in London, about 30% above the national guide, giving a range of £78,000–£156,000. Exact pricing depends on your home, so we only fix it once a free site survey is done.
| Type of job | What it usually involves | Guide in Hounslow |
|---|---|---|
| Small (15–20m² total) | A compact rear or side extension adding a small room on each floor. | £52,000–£84,000 |
| Typical (30–40m² total) | A larger kitchen or living room below with a double bedroom or en-suite above. | £78,000–£156,000 |
| Large (50m² plus total) | Wide or deep extensions, often with a new bathroom, steelwork and high-spec glazing. | £130,000–£234,000 |
The main things that change the figure:
- Combined floor area across both storeys
- How the new roof joins the existing roof
- Bathrooms, en-suites and plumbing on the upper floor
- Scaffolding duration, access and the level of finishes
What does the job include in Hounslow?
- Groundworks, foundations and below-ground drainage
- Insulated cavity walls with brick or render to match the house
- First-floor joists, stud walls and new openings upstairs
- Roof structure tied into the existing roof, tiled to match
- Electrics, plumbing and heating by qualified trades, with certificates
- Building control inspections and completion certificate
What are homes like around Hounslow?
London's housing is dominated by Victorian and Edwardian terraces, often in yellow London stock brick, with Georgian terraces in central districts and mansion blocks across many inner areas. Outer boroughs have large belts of interwar semis, and there are extensive post-war council estates. Many houses have been split into flats, and conservation areas are widespread.
Terraces suit side-return extensions and rear dormer loft conversions; interwar semis commonly take hip-to-gable lofts. Shared party walls, restricted parking and conservation rules often shape the plans and the programme.
In Hounslow, as elsewhere in London, we take the building's age and construction into account before recommending anything, because both can change what is involved in a double-storey extension.
Permissions for a double-storey extension in Hounslow
Planning law differs across the UK. For a home in Hounslow, it is the England rules below that count, and we check them with the council ahead of any quote.
In England, a two-storey rear extension can only be permitted development if it is no more than 3 m deep, at least 7 m from the rear boundary and finished to match the house. Most double-storey and all two-storey side extensions need full planning permission.
Building Regulations approval is needed, with structural calculations for beams, foundations and the roof. The Party Wall etc. Act 1996 often applies on semi-detached and terraced houses.
Rules change and every property is different, so we check the planning history and constraints for your address before we quote.
From survey to handover
Free site survey
We begin by looking at the job in person. During the free survey we discuss options, materials and budget for a double-storey extension, and photograph or measure anything the quote needs to reflect.
Your fixed price
Next you receive a written quote with a fixed price for the agreed specification. It lists what is included, what is not, and how payments are staged, so you can compare it properly.
Dates and permissions
Before anyone starts, we confirm the programme in writing, check whether consents are required and arrange deliveries. If a skip or scaffolding on the road needs a permit, we apply for it.
On site to finish
Our trades complete a double-storey extension while your point of contact keeps you updated. When everything is finished, we clear the site, take away waste and go through the result with you before handover.
What you can expect from us
Common questions
Can I stay at home during the work?
In most cases, yes. Most people can live at home throughout, and we plan the work to keep disruption down by protecting floors, agreeing working hours and keeping access routes clear. Bigger jobs affecting kitchens, bathrooms or heating may mean a short spell with reduced facilities, and we talk this through with you at the survey.
Is a double-storey extension better value than single-storey?
A double-storey extension usually gives better value per square metre than a single-storey one, because the same foundations and roof serve twice the floor area. The overall cost is higher, and planning can be harder because of the effect on neighbours. If you might want an extra bedroom later, building both floors now avoids a second round of disruption and scaffolding.
What happens at the survey?
We visit your home at a time that suits you, look at the area involved, take measurements and check access, condition and any services that might be affected. We talk through what you want from a double-storey extension, explain the options and answer questions. There is no charge and no obligation; afterwards we send a written quote.
Do I need planning permission for a two-storey extension?
Most two-storey extensions need planning permission, but it depends on the size, height and position, your home's location, whether it is listed or in a conservation area, and which UK nation you are in. In England, a two-storey rear extension can sometimes be built under permitted development if it is no deeper than 3m and at least 7m from the rear boundary. We check what applies before quoting.
How much does a double-storey extension cost?
A typical double-storey extension of 30–40m² across both floors costs £78,000–£156,000, built to a plastered finish. As a rough guide, allow around £1,400–£2,600 per square metre plus fixed costs for groundworks, scaffolding and fees. The second storey usually costs less per square metre than the first, because foundations and roof are shared. Bathrooms upstairs and a complex roof add most. We confirm a fixed price after the survey.
Near Hounslow
Coverage for Hounslow spans TW3, TW4, TW5 and TW7. Close by, Isleworth, Heston and Richmond are covered too, and the rest of our UK-wide area follows the same survey-then-quote process from start to finish.