Kitchen extension cost: price the building and the kitchen separately

How kitchen extension cost works

1. Settle whether it is permitted development. A great many kitchen extension are permitted development, which means no planning application, but the limits on depth, height, materials and how much of the plot is already built on are specific and a designer should read them against your own house before anybody prices anything.
2. Get drawings and a structural design. Existing and proposed drawings, then a structural engineer's calculations for whatever is being opened up or carried. On a kitchen extension this is a small share of the total and it is what turns an idea into something three builders can price identically.
3. Serve the party wall notices in time. Work on or near a shared wall, or excavation within three or six metres of a neighbour's foundations, engages the Party Wall etc. Act and the notice periods are set in months rather than weeks. Serving late is the commonest reason a start date slips.
4. Price it against a specification, not a sketch. Ask each builder to price the same written specification, with provisional sums shown as provisional sums. Two quotes that differ by a third almost always differ in what is included: the kitchen, the flooring, the decoration and the drainage diversion are the usual absentees.
5. Agree stages, retention and building control. A staged payment schedule against completed work, a small retention until sign-off, and a clear statement of who is notifying building control. The completion certificate is what a future buyer's solicitor will ask for.

Insurance and paperwork

Common questions

Does the kitchen need to be designed before the extension is priced?

Not fully, but its position does. Where the sink, the hob and the appliances sit determines the drainage, the ventilation and much of the electrical work, and moving them later is the change that costs most on site.

What about the drainage?

A new kitchen normally needs a waste connection, and where the existing drainage runs decides whether that is straightforward. Building near or over a public sewer brings the water company into the process, which takes time.

Is a rooflight or a lantern worth it?

In a deep single storey extension it is usually what makes the middle of the room usable. It is also a roof penetration with a flashing detail that has to be right, so it belongs in the specification rather than added as an afterthought.

How much does a kitchen extension cost UK-wide?

It is two prices worth seeing separately. The building work is groundwork, structure, roof, glazing and services; the kitchen is cabinetry, worktops, appliances and installation, and it can range further in price than the extension around it. Ask for the two to be split before comparing quotes.

Registered contractors by region

• Registered roofers in the East Midlands postcode area
• Registered roofers in the East of England postcode area
• Registered roofers in the London postcode area
• Registered roofers in the North East postcode area
• Registered roofers in the North West postcode area
• Registered roofers in the Scotland postcode area
• Registered roofers in the South East postcode area
• Registered roofers in the South West postcode area
• Registered roofers in the Wales postcode area
• Registered roofers in the West Midlands postcode area
• Registered roofers in the Yorkshire and The Humber postcode area