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.
Whatever prompted you to look into a double-storey extension, whether wear and tear, a growing family or plans to move, we can survey your Slough home and give you a price in writing. Homes in the South East typically come in at £67,000–£134,000, VAT included, for this kind of work. We also cover Windsor, Maidenhead and Gerrards Cross, and the same steps apply wherever you are in Berkshire.
- Guide price
- £67,000–£134,000 inc VAT
- Time on site
- 14–22 weeks on site
- Postcodes
- SL1, SL2 and SL3
- Planning rules
- England
- Local area
- Berkshire
- Survey
- Free, with a written quote
How much does a double-storey extension cost in Slough?
To help you plan, we show what a double-storey extension typically costs in Slough instead of holding figures back for a sales call. The range is £67,000–£134,000 with VAT, using rates in the South East that are about 12% above the national guide. A free survey then fixes your actual price.
| Type of job | What it usually involves | Guide in Slough |
|---|---|---|
| Small (15–20m² total) | A compact rear or side extension adding a small room on each floor. | £45,000–£73,000 |
| Typical (30–40m² total) | A larger kitchen or living room below with a double bedroom or en-suite above. | £67,000–£134,000 |
| Large (50m² plus total) | Wide or deep extensions, often with a new bathroom, steelwork and high-spec glazing. | £112,000–£202,000 |
Expect these to shape the final quote:
- Combined floor area across both storeys
- How the new roof joins the existing roof
- Bathrooms, en-suites and plumbing on the upper floor
- Foundation depth, ground conditions and drains to divert
Scope of the work
- 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
- Scaffolding for the full build, erected and inspected
- Electrics, plumbing and heating by qualified trades, with certificates
- Windows, external doors, plastering and internal doors
Local housing and a double-storey extension
Reading's Victorian terraces often show the town's patterned red and silver-grey brickwork, while Windsor, Maidenhead and Newbury mix Georgian, Victorian and Edwardian houses. Bracknell grew as a post-war new town with planned estates, Slough has a great deal of interwar and post-war housing, and newer developments sit on the edge of most towns.
Much of the Thames Valley is low-lying, so flood risk and clay ground near the river can influence foundations and drainage for extensions.
None of this holds for every street in Slough, which is why we look at your actual house before pricing a double-storey extension rather than assuming from its age alone.
Planning and building rules in Slough
For anyone in Slough, the relevant framework is England's. The summary below is general, so we always contact the council about your address before putting a price in writing.
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.
How does the job run?
We look at the job
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.
Written quote
We put everything into a written, fixed-price quote: the specification, what's excluded, staged payments and the expected time on site. Take whatever time you need to decide; there's no pressure to commit.
Dates and permissions
Preparation matters as much as the build. We agree access, parking and working hours with you, order materials in good time, and confirm any permissions so the job isn't held up once it starts.
Finish and handover
On site, the agreed plan is followed and any change is put in writing first. At completion we do a final clean, go through the snagging list with you and leave you with the relevant documents.
Why homeowners choose us
Questions about a double-storey extension in Slough
Can we live at home while it is built?
Most families stay at home during a double-storey extension. The new structure is built outside first, and we only break through into the existing rooms near the end, usually one floor at a time. Upstairs, this may mean a bedroom is out of use for a week or two. We fit dust screens, protect floors and stairs, and plan any time without water or power in advance.
Do I need planning permission in Slough?
It depends on the work, the size of the project, your property type and whether the building is listed or in a conservation area. Slough is in England, so England's rules apply. Many smaller jobs need no planning application, but some still need building control approval. We check what applies to your address before quoting.
Can the new upstairs room have its own bathroom?
A new upstairs room can usually have an en-suite, provided waste pipes can reach the soil stack or a new one can be installed. Running the waste pipe to the right falls is the main design question, and a pumped system is an option where gravity will not work. We plan bathroom positions at the design stage so pipes, ventilation and insulation are built in rather than added later.
Who do I deal with during the job?
One point of contact manages your project from survey to handover. They schedule the trades working under our contract, keep you updated on progress, and are the person to call with any question. You don't need to coordinate builders, electricians or decorators separately, because that is part of what we do.
Will the extension affect my neighbours?
A double-storey extension can affect neighbours' light, outlook and privacy, which is why planning departments look closely at height, depth and window positions. Side windows facing neighbours often need obscure glass. Work near a shared wall may also need party wall notices; the Party Wall etc. Act 1996 applies in England and Wales only. We talk through these points early so the design is realistic.
Nearby towns
Live in Slough? Our coverage takes in the SL1, SL2 and SL3 postcode areas and reaches out to Windsor, Maidenhead and Gerrards Cross, so homes on the outskirts and in the next town along are included.