Two-storey extensions for semi-detached houses in Feltham

Feltham: the key facts for this kind of project.

Postcode districts: TW14
County / area: Greater London, England
Price region: London
Guide price: £67,000–£90,500 (£2,400–£3,240 per m²)
Approval route: Depends on position: a two-storey rear extension may be permitted development (3 m deep, 7 m from the rear boundary); a two-storey side extension needs planning permission.
Nearest towns: Hanworth (1.6 miles), Cranford (2.1 miles), Ashford (Surrey) (2.1 miles)
First visit: Free, no obligation

About a two-storey extension for a semi-detached house

A two-storey extension for a semi-detached house is a two-floor addition to the rear, the open side, or both, designed around the attached neighbour on one side. The rear is often the simplest option and can sometimes be permitted development, while a side extension uses the gap on the detached side. Both need care with the shared party wall and the neighbour's light.

We cover Feltham (TW14) and the places around it, including Hanworth (1.6 miles), Cranford (2.1 miles) and Ashford (Surrey).

What it costs in Feltham

For budgeting in Feltham, allow around £67,000–£90,500 for a two-storey extension for a semi-detached house with a 4 m × 3.5 m footprint on two floors (28 m² of new floor space). That's based on £2,400–£3,240 per m² including VAT for London. Kitchens, bathroom fittings and flooring are priced separately so you can compare like with like.

Spec	Per m²	A 4 m × 3.5 m footprint on two floors (28 m² of new floor space)
Essential	£2,210–£2,980 per m²	£62,000–£83,500
Standard	£2,400–£3,240 per m²	£67,000–£90,500
Premium	£2,880–£3,890 per m²	£80,500–£109,000

Planning and building regulations in Feltham

In England, a two-storey rear extension on a semi can be permitted development if it goes no more than 3 m beyond the original rear wall and stays 7 m from the rear boundary, with matching materials and roof pitch. A two-storey side or wraparound extension always needs planning permission, costing £548 (or £575 for applications made from 8 December 2026). Protected areas such as conservation areas exclude two-storey rear permitted development.

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 Feltham homes

The attached neighbour's light

A two-storey rear extension next to the party wall can take light from the neighbour's rear windows. Councils often use a 45-degree test, so the first floor may need to be shorter than the ground floor or set in from the shared boundary.

Keeping the pair balanced

Semis are designed as matching pairs, and a side extension changes that balance. Setting the side extension back from the front wall and keeping its ridge lower helps the pair still read as a pair, which councils' design guides commonly ask for.

How we'd run your project

Start at your house
We come to your home in Feltham, measure up, check the ground floor walls and roof structure, and note anything near the boundaries.
Get it approved
Once you're happy with the design we submit it to the council for Feltham and deal with any questions from the planning officer.
Fixed price in writing
With approved drawings and calculations, we give you a fixed build price and a programme you can plan around.
Build
Foundations, walls, floor, roof, windows, then first and second fix. We break through into the house as late as we can.

Questions about two-storey extensions for semi-detached houses in Feltham

Who handles building regulations for a project in Feltham?

We handle it as part of the project. What's needed in England: building regulations approval (full plans recommended) from the council or a registered building control approver, with a completion certificate at the end. We prepare the drawings and the engineer's calculations, book the inspections and pass you the completion paperwork at the end.

How much does a two-storey extension for a semi-detached house cost in Feltham?

Our guide for London, which covers Feltham, is £2,400–£3,240 per m² including VAT. A typical project with a 4 m × 3.5 m footprint on two floors (28 m² of new floor space) comes to about £67,000–£90,500. Design and approval fees are extra, and we fix the build price in writing once the design is agreed.

How long does a two-storey extension for a semi-detached house 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.

Should I extend my semi to the side or the rear?

It depends on your plot and what you need. A rear extension keeps the side drive and can sometimes be permitted development, but it affects the attached neighbour. A side extension keeps the rear garden but always needs planning permission in England. We compare both at the free site visit.

Will a side extension make my semi look like a terrace?

It can if it fills the whole gap to the boundary at first floor and the neighbour does the same. Many councils ask for a first-floor gap to the side boundary or a set-back for this reason. We design the extension to keep the semi reading as one of a pair.

Nearby

Other towns near Feltham:

Other extensions in Feltham

All two-storey extension services in Feltham · Two-storey extensions for semi-detached houses across Greater London

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