Kitchen Extension Cost: What Affects the Price

A kitchen extension is one of the most popular ways UK homeowners open up their ground floor — but it's genuinely two projects layered together: a structural extension, and a full kitchen fit-out inside it. Understanding both halves separately is the key to budgeting accurately.

How the cost combines

Start with the structural extension cost — see our full single-storey extension cost guide for realistic ranges by size — then add the kitchen fit-out itself: units, worktop, appliances, plumbing and electrical work specific to the kitchen. A mid-range kitchen fit-out typically adds a further £14,000–£22,000 on top of the extension's own structural cost, though this varies enormously with specification, same as any kitchen project.

A worked example

A 20m² rear extension for a new kitchen-diner: structural shell and basic fit-out (flooring, decoration, standard finishes) at £2,500–£3,500/m² is roughly £50,000–£70,000, per our single-storey extension cost guide. Add a mid-range kitchen — units, worktop, appliances, and the kitchen-specific plumbing/electrical — at £14,000–£22,000, and the realistic combined total lands around £64,000–£92,000. A budget-specification kitchen brings that down; a high-end kitchen with an island and premium appliances pushes it up considerably further.

What's genuinely different about a kitchen extension

Combined first-fix work

Plumbing and electrical first-fix for the extension's structure and for the kitchen itself happen together, but they're still two distinct scopes — kitchen appliance circuits, sink and dishwasher plumbing, and island services (if included) are all on top of the extension's own first-fix needs.

Structural openings for glazing

Kitchen extensions often feature large sliding or bi-fold doors onto the garden, which need more substantial structural openings than a standard window — a genuine cost driver beyond a simpler reception-room extension.

Island and layout considerations

If the new space allows for a kitchen island, that adds its own plumbing/electrical routing (if it includes a sink or hob) and structural floor considerations, on top of the base kitchen cost.

Drainage and utility relocation

Moving a sink, dishwasher, or waste run into a new part of the house sometimes means extending existing drainage runs further than a straightforward like-for-like kitchen refit would — worth flagging to your contractor early, since a longer run or a change in fall (the pipe's slope) can affect both cost and feasibility.

Extending vs renovating your existing kitchen

This is a genuinely important distinction, not just wording — see our kitchen renovation cost guide if your existing kitchen footprint is workable and you just want a better version of it. A kitchen extension makes sense specifically when you need more floor space than your current kitchen has, not purely for a cosmetic refresh.

A quick decision checklist

• Is the limitation genuinely floor space, or is your current kitchen footprint workable with a better layout and finish? (If the latter, see our kitchen renovation cost guide instead.)
• Does the new layout need a kitchen island, and does that fit the available structural floor and services routing?
• How far does drainage need to run to the new location, and has that been checked against existing waste runs?
• Is the glazing specification (bi-fold/sliding doors vs standard windows) decided before quotes are compared, since it materially affects both structural and finishing cost?

Avoiding the common pitfalls

See our common extension mistakes guide and extension labour costs guide for the structural side of the project — the same planning, contingency, and sequencing principles apply, with the kitchen fit-out as an additional layer on top.

Getting an accurate figure

Because a kitchen extension combines two distinct scopes of work, the only reliable way to get an accurate total is a proper site visit covering both the structural extension and the kitchen specification together — a quote for one without the other will understate the real total.