Extension Cost · Cobham

How much does an extension cost in Cobham?

Cobham prices at the South East baseline BuildLens builds from, in the heart of the Surrey estate belt — where the stock is newer, the surprises are fewer, and the cost is driven by scale and specification rather than fabric. A single-storey rear runs from a shell figure around £3,575 per m² to an all-in nearer £5,882.

Cost your Cobham 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 Cobham, a single-storey rear looks like this per square metre.

The headline
you find

£3,575

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

What you
actually pay

£5,882

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

On a typical 30 m² rear in Cobham, that is roughly £150,000 to £175,000 all-in — against a shell headline nearer £107,000. 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 at the BuildLens South East baseline, priced on current trade 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.

What moves the number in Cobham

Cobham inverts the usual South East story: the fabric is the easy part, and the setting does the shaping.

The estate belt

Much of Cobham's stock sits on private roads and gated estates, and the estates come with rules — working hours, access arrangements, deliveries, contractor conduct. None of it changes the build cost per square metre; all of it shapes the programme, and a programme that runs longer carries its preliminaries longer.

Newer stock, fewer surprises

Cobham's houses are largely modern by South East standards, which means less of the period overhead that dominates elsewhere in this list — no lath-and-plaster, predictable structures, services that renew cleanly. The build base behaves; the variables sit above it.

Top-tier expectations

The specification the local market expects sits at the top of every tier — glazing, finishes and fit-out included. Cobham projects are large and specified high, and the totals follow.

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 Cobham calibration of it.

Extension cost — the full breakdown →

Common questions about extension cost in Cobham

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

Calibrated to Cobham, the shell runs around £3,575 per m² and the all-in — with a fitted kitchen, fees, contingency and VAT — nearer £5,882. A typical 30 m² rear therefore lands roughly £150,000 to £175,000 all-in. The figure depends heavily on the specific property, which is what a desktop analysis of your address sets out.

Why do Cobham 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 Cobham: estate rules that shape the programme, and a market that specifies at the top of every tier. The quote is usually not high; the headline was incomplete for this property in this place.

Do private estate rules change extension cost in Cobham?

They change the programme more than the rate. Estate rules on working hours, access and deliveries stretch the calendar, and preliminaries run for as long as the job does — so the same build takes longer and carries its site costs further. It is a fixed feature of estate addresses, and entirely predictable from the property.

What pushes a Cobham 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.