What does a Grade II kitchen extension cost in 2026?

The honest answer is “it depends”, and the honest answer is also that most of the variance comes from four things, not forty. If you’re a kitchen designer being asked the question on a first call, or a homeowner trying to sense-check a quote, here’s where the number actually lives in 2026.

For a Grade II listed property — a Georgian rectory, a Victorian townhouse, a farmhouse with the original hearth still in the wall — a single-storey rear extension with the kitchen relocated into it sits, today, somewhere between £180k and £420k all-in. That’s build plus kitchen plus the bits the homeowner forgets, on a project that gets through Listed Building Consent without a planning enforcement round.

The range is wide because four numbers move it.

The build envelope: £2,800–£4,200 per square metre

For a heritage rear extension with traditional construction — lime mortar, hand-made brick, cast lead detail, slate or hand-tile roof — you’re looking at £2,800 to £4,200 per square metre of new floor area in 2026. The bottom of that range assumes a contractor who has done three or four listed jobs and isn’t learning on yours. The top is a heritage main contractor with a conservation accreditation, working through a heritage consultant.

A 35 m² rear addition — typical for a kitchen-dining-utility footprint — therefore comes in between £98k and £147k for the shell alone. That’s before the kitchen.

The kitchen scope: £55k–£180k

The bespoke kitchen on a Grade II project rarely lands below £55k in 2026. Below that and you’re in the semi-bespoke market, which the homeowner has usually already ruled out by the time they’ve commissioned a heritage architect. The top of the range — £180k and up — covers the projects where the cabinetry is genuine joinery, the worktops are stone the homeowner has visited a yard to choose, and the appliance package crosses six figures.

For Plain English, deVOL Heritage, Roundhouse, or a similar tier of maker, a working rule of thumb is £85k–£140k for the cabinetry and worktops, plus £20k–£40k for appliances. The variance there is mostly down to two things: how much glazing eats into the wall runs, and whether the island gets a proper stone slab or a quartz composite.

Almost every cost surprise on a Grade II kitchen project, in our experience, traces back to something the architect drew that the contractor priced for the easy version of, and the conservation officer asked for the difficult version of.

The heritage premium: 12–22%

Listed Building Consent adds 12% to 22% to the total project cost compared to the same square metres on an unlisted property. The premium goes on three things:

First, materials. Hand-made brick is roughly 3.5× the cost of standard stock; lime mortar takes longer to lay; lead flashing on a parapet is detail-heavy. Second, labour. Heritage builders are a smaller pool, and they don’t discount for scarcity. Third, redesign rounds. The conservation officer almost always asks for something to change between the planning submission and the final consent, and the cost of that round tends to land on the kitchen designer’s scope as a knock-on.

The bit homeowners forget: £18k–£45k

Across a sample of fifty Grade II kitchen extensions filed in 2024 and 2025, the median “everything else” line — heritage consultant fees, structural engineer, party wall agreements, building control, planning fees, drainage, asbestos survey, the bat survey if the roof has been opened — came in at £27k. The bottom decile was £18k; the top decile was £45k.

It is the line that most often goes missing from a homeowner’s mental budget, because it doesn’t turn up on the architect’s fee proposal and it doesn’t turn up on the kitchen designer’s quote. It turns up two-thirds of the way through the build, when the structural engineer asks for revisions to the steels and the homeowner pays the architect another £4k to redraw them.

What this looks like as a number

For a 35 m² heritage rear extension with a £95k–£140k bespoke kitchen and a £30k appliance pack, the working all-in is:

Build at £3,400/m² mid-range: £119k. Kitchen plus appliances: £150k. Heritage premium on the build: £21k. Everything else: £27k. That’s £317k — comfortably inside the £180k–£420k range and almost exactly on the median for projects we see going through in 2026.

Where the number can quietly double

Two situations turn a £300k project into a £600k project, and they don’t always announce themselves at the planning stage:

A new structural opening through a load-bearing chimney breast. The conservation officer either disallows it (cheap) or allows it with a heritage steel detail (very expensive, occasionally unsolvable without a redesign of the kitchen layout).

A change in floor level. If the architect has drawn a step down into the new extension and the homeowner decides at month four that they want the floors to flow flat, the underpinning bill alone can run to £40k, and it puts a six-week pause on the kitchen install.

Both of these are, generally, visible in the architect’s drawings at the planning submission. The kitchen designer who reads the drawings carefully — and flags either of them on the first conversation with the architect — is the kitchen designer the homeowner remembers when the contract goes out.

What we’d use to pressure-test a quote

If you’re looking at a quote from a contractor or a kitchen maker on a Grade II project and trying to work out if it’s realistic, the quick gut check we use:

The total of build plus kitchen plus appliances should sit between 4.0× and 5.5× the m² figure. Anything below 4.0× and someone has either not priced the heritage premium or has assumed they can persuade the conservation officer to drop a requirement. Anything above 5.5× and there’s usually a stone slab island or an appliance package the homeowner hasn’t realised they’ve agreed to.

It isn’t a rule. It’s a sniff test, and it has saved us — and the designers we’ve been working with — a week of pricing arguments more than once.