Extension Cost · Chiswick

How much does an extension cost in Chiswick?

Chiswick sits toward the top of the national range, and its housing does most of the pushing — Victorian and Edwardian terraces built street after street, with Bedford Park setting a conservation standard the rest of W4 tends to follow. A single-storey rear here runs from a shell figure around £3,930 per m² to an all-in nearer £6,470.

Cost your Chiswick extension See a sample report

The figure you find isn't the figure you pay

As everywhere, most cost guides quote a shell rate — the bare build. It is not what lands on your account. Calibrated to Chiswick, a single-storey rear looks like this per square metre.

The headline
you find

£3,930

Shell only — structure, roof, envelope. Per m².

What you
actually pay

£6,470

All-in with a fitted kitchen, fees, contingency and VAT. Per m².

On a typical 30 m² rear in Chiswick, that is roughly £190,000 to £215,000 all-in — against a shell headline nearer £120,000. The difference is the fit-out, the professional fees, the contingency and the VAT the shell figure never included. Where in that range you land depends heavily on the property.

Figures calibrated from BuildLens South East build data — around 10% above the regional baseline — priced on current day rates and live merchant pricing (2026). The all-in assumes an entry-level bespoke kitchen from local joinery; a higher kitchen tier moves it further.

Why Chiswick sits above the national range

Two forces push Chiswick costs up, and they compound. Labour across west London prices at London rates, and the stock is almost entirely period — which carries an overhead of its own before any question of finish.

Bedford Park sets the tone

One of the earliest garden suburbs in the country, Bedford Park is tightly protected, and external alterations there face close control on materials, joinery and rooflines. Even outside its boundary, the standard it sets shapes what the local market considers acceptable — and what it costs to deliver.

The side return is the local archetype

Chiswick's terrace grid makes the side-return infill, usually combined with a rear knock-through, the defining local project. Access is through the house on most streets, skips and parking suspensions need arranging on narrow roads, and the preliminaries climb accordingly. A rear plus a side return is priced as two extensions, never one.

Finishing expectations are W4-grade

Chiswick properties expect a standard of finish that demands experienced trades rather than fast ones. Tilers, joiners and decorators command a premium here, and it is the most visible place the local labour rate lands.

Where the money goes, itemised. The full anatomy of an extension — substructure through fit-out — and how BuildLens builds the number from method and live pricing, sits on the main extension cost page. This page is the Chiswick calibration of it.

Extension cost — the full breakdown →

Common questions about extension cost in Chiswick

How much does a single-storey rear extension cost in Chiswick?

Calibrated to Chiswick, the shell runs around £3,930 per m² and the all-in — with a fitted kitchen, fees, contingency and VAT — nearer £6,470. A typical 30 m² rear therefore lands roughly £190,000 to £215,000 all-in. The figure depends heavily on the specific property, which is what a desktop analysis of your address sets out.

Why do Chiswick quotes differ from the national averages online?

Because most published figures are shell rates without fit-out, fees, contingency or VAT — and because they know nothing about Chiswick: period surprises in Victorian fabric, and the side-return preliminaries that narrow terrace streets impose. The quote is usually not high; the headline was incomplete for this property in this place.

Does Bedford Park's conservation status add to extension cost?

Yes, and measurably. External alterations in Bedford Park face close control on materials, window joinery and rooflines, which means formal applications, design iteration and conservation-grade detail as real line items before site work begins. Outside the boundary the controls relax, but the finish standard the area expects does not.

What pushes a Chiswick extension over budget?

The property and the fit-out, usually — a kitchen or bathroom specified above the budget it was set against, and the local conditions above surfacing mid-job instead of being priced upfront. Both are predictable once the specific property is assessed, which is exactly what a BuildLens report does before you commit.