Extension Cost · Islington

How much does an extension cost in Islington?

Islington sits toward the top of the national range, and its Georgian and Victorian terraces are the reason — handsome, protected, and demanding to build off. A single-storey rear here runs from a shell figure around £3,930 per m² to an all-in nearer £6,470, and the borough's access constraints push preliminaries higher than most of London.

Cost your Islington 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 Islington, 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 Islington, 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 Islington sits above the national range

Islington combines three cost drivers most areas only have one of: genuinely old fabric, near-blanket conservation coverage, and terrace streets with no rear access. Each is manageable; together they explain why the borough prices where it does.

Georgian fabric and listed squares

Much of the borough sits within conservation areas, and the Georgian terraces and garden squares carry listing across whole streets. Older fabric is less forgiving than Victorian — thinner walls, shallower footings, floor structures that need more work to accept modern loads — and consents take longer where listing applies.

Everything arrives through the front door

Most Islington terraces have no rear access. Demolition arisings leave and materials arrive through the house, by hand, with parking suspensions arranged on the street. That is labour, programme and protection measures a national average never accounts for, and it lands in the preliminaries on every job.

Lower-ground works are common

Islington kitchens frequently sit at lower-ground level, which brings tanking, level changes and light wells into scope. It is standard local work, and it is priced — but only if the figure you started with knew it was there.

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 Islington calibration of it.

Extension cost — the full breakdown →

Common questions about extension cost in Islington

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

Calibrated to Islington, 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 Islington 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 Islington: Georgian fabric that needs more work than it looks, and the through-the-house logistics of terraces with no rear access. The quote is usually not high; the headline was incomplete for this property in this place.

Does having no rear access really change the cost of an Islington extension?

Yes, more than most people budget for. When every skip-load leaves and every steel arrives through the front door, the labour hours climb, the programme stretches and the protection measures multiply. It is one of the quieter reasons Islington preliminaries run above the London norm, and it is entirely predictable from the property's position.

What pushes a Islington 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.