Extension Cost · Sevenoaks

How much does an extension cost in Sevenoaks?

Sevenoaks prices at the South East baseline BuildLens builds from, but its stock does not build baseline projects — the detached houses here take large extensions, and the totals follow the footprints. A single-storey rear runs from a shell figure around £3,575 per m² to an all-in nearer £5,882.

Cost your Sevenoaks 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 Sevenoaks, 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 Sevenoaks, 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 Sevenoaks

Sevenoaks costs are driven by scale and setting more than rate — the arithmetic is the baseline, but almost nothing about the projects is.

Large houses, large projects

The town's detached stock takes extensions the terrace grid never could: full-width rears, wraps, double-height additions. At the same per-square-metre rate, a 45 m² Sevenoaks rear simply costs half as much again as the 30 m² norm — size is the first variable to fix before any rate means anything.

The Kent Downs setting

Sevenoaks sits against the Kent Downs, and addresses within or adjoining the protected landscape face additional control on design and materials. On the rural lanes, access and deliveries shape the programme in ways a town site never sees.

Period houses and oasts carry their own overhead

The area's period stock — and its converted oasts and farm buildings — need structural work sized for the actual fabric and materials matched to it. Standard local work, priced after assessment.

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 Sevenoaks calibration of it.

Extension cost — the full breakdown →

Common questions about extension cost in Sevenoaks

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

Calibrated to Sevenoaks, 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 Sevenoaks 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 Sevenoaks: footprints that run well above the norm, and the landscape controls that apply toward the Downs. The quote is usually not high; the headline was incomplete for this property in this place.

Does the Kent Downs designation affect extension cost around Sevenoaks?

For addresses within or adjoining it, yes. The protected landscape brings additional control on design and materials, with the applications and specification that implies, and rural-lane access can shape deliveries and programme. In the town itself, standard consents apply outside the conservation core.

What pushes a Sevenoaks 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.