Two-storey side extensions in Carshalton
A two-storey side extension is one of the most space-efficient ways to add bedrooms and living space to a house in Carshalton, because the new floors share one set of foundations and one roof.
What we'd confirm first for a project in Carshalton.
- Postcode districts
- SM1 and SM5
- County / area
- Greater London, England
- Price region
- London
- Guide price
- £103,500–£138,500 (£2,460–£3,300 per m²)
- Approval route
- Planning permission is needed: in England, permitted development only allows single-storey extensions to the side.
- Nearest towns
- Wallington (0.7 miles), St Helier (1.2 miles), Sutton (1.9 miles)
- First visit
- Free, no obligation
About a two-storey side extension
A two-storey side extension suits a detached or semi-detached house with a side garden, driveway or garage wide enough to build on. You get a design that sits comfortably on the street, a planning application or permitted development check depending on your nation, structural design, building regulations approval and the build itself. We manage the whole process, and the work is carried out by vetted teams working under S&K.
Around Carshalton we also work in Wallington, St Helier and Sutton, and across the rest of Greater London. Postcode districts in and near Carshalton: SM1 and SM5.
What it costs in Carshalton
In London, which includes Carshalton, we'd expect a two-storey side extension to cost around £103,500–£138,500 for a 3 m × 7 m footprint on two floors (42 m² of new floor space), or £2,460–£3,300 per m² including VAT. We'll give you a written design-stage price first, then a fixed build price once the drawings are agreed.
| Spec | Per m² | A 3 m × 7 m footprint on two floors (42 m² of new floor space) |
|---|---|---|
| Essential | £2,260–£3,040 per m² | £95,000–£127,500 |
| Standard | £2,460–£3,300 per m² | £103,500–£138,500 |
| Premium | £2,950–£3,960 per m² | £124,000–£166,500 |
Planning and building regulations in Carshalton
In England, a two-storey side extension always needs householder planning permission, because permitted development only allows single-storey extensions beyond a side wall. The fee is £548 (or £575 for applications made from 8 December 2026), and councils should decide within 8 weeks of validation. Expect them to look at set-back, roof height, gaps to the boundary and the effect on neighbours.
Approval in England: Householder planning application: £548 (or £575 for applications made from 8 December 2026). Lawful development certificate: £274 (about £288 for applications from 8 December 2026). Councils should decide householder applications within 8 weeks of validation.
Building regulations: Building regulations approval (full plans recommended) from the council or a registered building control approver, with a completion certificate at the end.
Design points for Carshalton homes
Matching the ridge and roof
A hipped house usually needs a hipped extension roof, and a gabled house a gable. Matching the pitch, tiles, ridge detail and brick bond is what makes a side extension look original rather than added, and councils look closely at it on a front-facing addition.
Access and services
Side extensions often cover the only route to the back garden, a gas meter, soil pipes or a drain run. We plan bin and bike access, move meters and pipes where needed and check drains early, because these items affect both cost and layout.
How we'd run your project
Look at the house
We start in Carshalton with a free visit: measurements, photos, a look at the loft and drains, and a frank chat about budget.
Drawings and permission
Our designers produce plans and elevations, then we take care of planning or permitted development checks with the council covering Carshalton.
Detail and price
Construction drawings, engineer's calculations and building control sign-off, then a written fixed price for the build.
On site
One project lead runs the job, keeps you updated and arranges inspections at each stage until completion.
Questions about two-storey side extensions in Carshalton
How much does a two-storey side extension cost in Carshalton?
Our guide for London, which covers Carshalton, is £2,460–£3,300 per m² including VAT. A typical project with a 3 m × 7 m footprint on two floors (42 m² of new floor space) comes to about £103,500–£138,500. Design and approval fees are extra, and we fix the build price in writing once the design is agreed.
Which postcodes do you cover around Carshalton?
We cover Carshalton (SM1 and SM5) and nearby places including Wallington, St Helier and Sutton, plus the rest of Greater London. The first site visit is free.
Do I need planning permission for a two-storey side extension in Carshalton?
Carshalton is in England, so England planning rules apply. Planning permission is needed: in England, permitted development only allows single-storey extensions to the side. If in doubt, a lawful development certificate or a planning application gives you certainty before you build.
How long does a two-storey side extension take?
Allow 4 to 8 weeks for survey and design, then the approval period (councils should decide householder applications within 8 weeks of validation), then 4 to 8 weeks of technical design, which can overlap. The build itself usually takes 14 to 20 weeks, longer for large or complex designs.
Can I build a two-storey side extension over my driveway?
Yes, if the drive is wide enough for a useful room and the council accepts the design. You may lose off-road parking, which some councils weigh up, and the foundations need to suit the ground below. We check parking, drains and meter positions at the free site visit before any drawings are prepared.
Nearby
Close to Carshalton? We work across the area, including:
Other extensions in Carshalton
- Rear
- Wraparound
- Part two-storey
- Over a garage
- First floor
- Semi-detached
- Detached
- Kitchen and bedrooms
- Bedroom and en-suite
All two-storey extension services in Carshalton · Two-storey side extensions across Greater London
Want a figure first? Try our guide price tool, then book a free visit to firm it up.