House Extensions Chiswick
Single storey rear and double storey extensions in Chiswick, planning, structure and build under one contract.
- Rated 4.9 from 31 reviews on MyBuilder
- Single-storey rear extension from £40,000
- Free site survey, itemised quote
GS Renovation builds extensions across Chiswick, working with the side returns and rear closet wings of W4's Victorian and Edwardian terraces and the wider plots of its semis. We take on rear, side-return, wrap-around and double-storey projects from foundations to final fit-out, one accountable team throughout.
In Chiswick, a single-storey rear extension typically starts from £40,000, or £2,000 to £2,800 per m² (indicative London ranges, Architecture for London, Resi, MyBuilder and Checkatrade, 2026). GS Renovation Ltd, a building contractor based in Potters Bar, does the work in Chiswick: the structural engineer we appoint designs the structure, we build it, and building control signs it off.
Price guide
| Work | Indicative London range |
|---|---|
| Single-storey rear extension | from £40,000 |
| Rear extension, per m² | £2,000 to £2,800 |
| Side return, per m² | £2,400 to £3,200 |
| Wraparound, per m² | £2,400 to £3,200 |
| Double storey, per m² | £1,800 to £2,600 |
| Basement extension | see the basement page |
Indicative London ranges (Architecture for London, Resi, MyBuilder and Checkatrade, 2026), not a quotation. Prices checked September 2026. Full breakdown: Extension Costs & Planning.
Quick estimate for Chiswick
Chiswick range: choose above
Side return and kitchen extensions in Chiswick
The classic Chiswick project is filling the side return, the narrow strip beside the rear closet wing, to widen a cramped galley kitchen into an open-plan space that runs the full width of the house. We dig and pour foundations to suit the ground and any nearby trees, build the walls, and install the steel beams that carry the original rear wall once it comes out. Rooflights over the new zone bring daylight deep into the plan.
Because these are period terraces, we match brick and detailing where it shows and think hard about how the new roof meets the existing closet wing. Every W4 house is slightly different in plot width and orientation, so we plan drainage, party wall bearings and glazing around your specific layout. The result reads as part of the house rather than a bolt-on, with the structure and finishes handled together.
Housing in Chiswick
The Council Tax list puts Chiswick at about 16,410 homes, 59% flats against 41% houses; 51% went up before 1919, 15% between the wars and 34% after 1945. Most homes here are flats, and a flat in Chiswick has no householder permitted development rights, so extending one needs planning permission and the freeholder's consent.
Chiswick side return infills beside the closet wing
For a terraced house, Hounslow's residential extension guidelines cap a single storey rear extension at 3.05m deep, and 26% of Chiswick's homes are terraced houses. Where a W4 terrace has a closet wing at the back, that is the outrigger the guidance refers to, and the side return beside it is the obvious place to widen a kitchen. An infill beside an outrigger that runs deeper than Hounslow's maximum depths is held to two limits: eaves on the shared boundary no higher than two metres, and a roof pitch no steeper than 45 degrees.
That boundary height shapes the section of the extension more than its plan. A low eaves on the neighbour's side means the roof rises away from the shared wall, so the glazing, rooflights and ceiling height are all designed inside that slope. Survey the ground levels in both gardens, since a difference between them changes how much height the boundary really allows. The Residential Extensions Guidelines SPD (2017) has been superseded, so check that any neighbour's scheme you point to as a precedent was judged against the current guidance before relying on it in a Chiswick application.
Planning and permitted development in W4
Some Chiswick extensions fall under permitted development and some need a full planning application to Hounslow Council, and which one applies depends on your property. A single-storey rear extension within the size limits often proceeds under permitted development, including in a conservation area, unless an Article 4 direction removes it. In a conservation area a side-return infill counts as a side extension and needs permission, as do two-storey rear extensions and roof extensions; homes already extended may have used up the allowance, and flats have no householder permitted development at all. We check Hounslow's conservation area and Article 4 maps for your address at the survey stage.
Whichever route applies, the build itself must meet building regulations, and where you extend against a shared boundary the Party Wall Act brings notice duties with your neighbours. We coordinate the drawings, handle the council submission or the certificate of lawful development, and give you the drawings and programme your party wall notices need; you serve them as building owner, or your surveyor does. That way the paperwork and the construction stay joined up rather than becoming your problem to chase.
Double storey extensions in Chiswick
Under permitted development a two-storey rear extension can go no more than 3 metres beyond the original rear wall and must stay at least 7 metres from the rear boundary, and in a conservation area it is not permitted development at all. Many gardens are too short for the 7 metre rule, so a double storey extension in Chiswick often needs planning permission from Hounslow Council. On the 26% of homes that are terraced, the neighbours' windows usually decide the depth. The Strand on the Green Conservation Area in Chiswick was designated on 7 November 1968 and extended in 2001 (council source). Our double storey extension page explains the build, at £1,800 to £2,600 per m² across both floors.
- Side-return and rear extensions
- Drainage diversion and build-over agreements with the water authority
- Roof works and structural alterations at roof level
VOA Council Tax stock of properties, March 2025, for Chiswick North East, Chiswick South East, Chiswick South West and Chiswick Park. Counts rounded by the VOA.
The GS Renovation Difference in Chiswick
Chiswick clients choose GS Renovation because we run the extension end to end, foundations, steelwork, roof, a programme built around your party wall notices and the full fit-out, with clear advice on whether you need planning or can build under permitted development. Our founder's 30+ years on the tools means we understand side returns and closet wings and deliver a space that belongs to the house.
- Brick and mortar matched to the existing elevation
- Permitted development checked before you pay for a planning application
- Building control applications and inspections coordinated for you
Built a new extension at rear of property. Laid foundations, drainage, raised floor, new roof and completed all fixtures and interior decoration…
George always kept to commitments and arrived on time. He offered helpful suggestions during his initial visit and promptly provided a reasonably…
It's the second time I have hired George and he has been absolutely professional and the work he did resembles perfectly what I had in mind. Being an…
FAQ
Frequently Asked Questions about House Extensions Chiswick
How does your house extensions price in Chiswick compare with a national firm's?
A GS Renovation price for house extensions in Chiswick compares well with a national firm's because there is no head office to fund, and both should sit within £2,000 to £2,800 per m² for a rear extension (indicative). GS Renovation is the contractor doing the work at W4, not a broker adding a margin. Compare the scope, including permitted development or a planning application to Hounslow Council, not just the total.
Will my Chiswick side-return extension need planning permission?
It depends. Many single-storey rear and side-return extensions in W4 fall under permitted development, but a side-return infill in a conservation area counts as a side extension and needs planning permission, as does a two-storey scheme; a house already extended may also need an application to Hounslow Council. Either way the build needs building regulations approval, and a shared boundary brings party wall notices. We assess your specific property and handle the route that applies.
What happens to the drains under a Chiswick side-return extension?
They are surveyed first, because the side return is often where the kitchen waste and rainwater pipes run. Inspection chambers inside the new footprint are relocated or fitted with sealed covers, and new runs are laid to the falls Part H requires. If the pipe is a shared public sewer, building over or close to it needs Thames Water's consent, which can shape where foundations go.
How close to trees can I build an extension in Chiswick?
Close, but the foundations get deeper and possibly more complex the nearer a tree is. Roots draw moisture from the ground and shift it as seasons change, so the engineer designs footings to sit below that zone, sometimes with heave protection. Check whether the tree is protected before any root is cut, and allow for this in the programme because it is found at the first dig.
Can we keep living in our Chiswick house during a rear extension?
Most families do, because the old rear wall stays up while the new shell is built around it. Foundations, walls, roof and glazing go in first, then the steel is installed and the rear wall comes out once the new space is weathertight. That last stage is the disruptive one, so plan a temporary kitchen elsewhere in the house for those weeks.
What insulation standard does a Chiswick extension have to meet?
Current Part L standards apply to the whole extension, walls, floor, roof and glazing, regardless of the age of the house it joins. Large rooflights or a lantern in a Chiswick side return count against the glazing allowance, so they are balanced against better insulation elsewhere. Building control checks this at plan stage and again at completion, not just at the end.
Can the roof of a Chiswick rear extension become a first floor terrace?
Expect a refusal. Hounslow's residential extension guidelines say a balcony or roof terrace on the flat roof of a single storey rear extension is likely to harm neighbours' privacy, and such schemes will normally be refused. In a W4 terrace, where the back windows face each other at close range, that line is hard to argue. Design the roof for rooflights, falls and maintenance access, and look for outdoor space in the garden layout rather than on top of the kitchen.
Is written pre-application advice enough for a Chiswick extension, or is a site visit better?
Match the level of advice to the doubt. Hounslow offers householder pre-application advice on extensions in two forms: a written response only, with no meeting, or a dearer version with a site visit. For a side return that sits within the guidance, written advice is usually enough. Pay for the visit where the neighbour's windows, a change in ground level or the look of a period street is the real question.
Does a drain under a Chiswick side return change the building control application?
It can. Build over or within 3m of a public drain or sewer and Hounslow requires a full plans application, not a building notice. In a terrace the run under a side return may also serve the neighbouring houses, and a drain serving more than one property is generally public. Check the water company's sewer map, then a camera survey, before the application goes in. If the run is public, the route and possibly the foundation design change, so find out before the programme is set.
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