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Kitchen Extension: A Guide to Costs and Planning

kitchen extension
(Image credit: IQ Glass UK)

Adding a kitchen extension is the most popular extension project. 

Turning a kitchen into a multifunctional space that can act as the beating heart of a home is a tall order but can be achieved masterfully. 

This guide pulls together advice on the all-important topics any savvy kitchen extender should take on board before embarking on such a project, including planning permission, Building Regs, costs and how long it takes to build a kitchen extension.

If you need to extend to get the perfect kitchen design, here's everything you need to know.

(MORE: Get a quote for your new kitchen)

How Much Does a Kitchen Extension Cost?

The cost of a single-storey kitchen extension will vary depending on where you are in the UK, the complexity of the project, and the standard of build quality you are aiming for. 

For a basic quality build on a straightforward extension expect to pay in the region of £1,320 to £1,620/m²; around £1,700 to £2,000/m² for a good quality build and for an excellent quality build you’d be looking at anything between £1,800 to £2,500/m² or more. 

kitchen extension with island

The Cotswood inframe shaker kitchen from Crown Imperial starts from £15,000. (Image credit: Crown Imperial)

On top of this you’ll then have the cost of your kitchen units, plus the installation costs to factor in too, which can range, on average, from around £5,000 to £25,000 for a high street kitchen (plus appliances and fitting), with bespoke kitchens starting at around £25,000 (excluding install). 

Finally, remember to factor in any additional costs such as architects’ fees, Building Regs and planning fees, insurance, Party Wall Agreements and so on.

(MORE: Get a quote for your new kitchen)

Do I Need Planning Permission for a Kitchen Extension?

If you are going to be adding a kitchen extension to create your new multi functional space, then you may be covered under Permitted Development (PD) rights and therefore not require planning consent.

However, bear in mind that if your house is in a Conservation Area or national park, the amount of work you can do under PD is usually reduced.

To be covered under Permitted Development rights, a single-storey extension should:

  • be a maximum height of four metres
  • not extend beyond the original rear wall of the house by more than six metres if it is an attached house (i.e. semi-detached), or eight metres for a detached home
  • If you are adding a side extension, this must be single-storey with a width of no more than half that of the original house.

Then you will require planning permission regardless of whether you are adding an extension or knocking through a wall. If you have any doubts, you should check with your local planning department.

What Kind of Kitchen Extension Should I Add?

How you extend will largely depend on your budget and the space that’s available. If you have a terraced or semi-detached home with a kitchen to the rear, adding a small rear extension for an open-plan kitchen diner leading out to the garden could be the best solution.

If you have restricted garden space, then a small side-return kitchen extension could provide you with useful extra space.

Where budget and outside space allows, consider a large rear kitchen extension spanning the width of the house, incorporating an open-plan kitchen, dining and living space.

Aluminium bifold doors and casement window from IQ Glass used in extension

This contemporary extension features aluminium bifold doors, slim aluminium window and a frameless rooflight from IQ Glass. The brick and wood cladding tie the extension in with the materials used on the original house (Image credit: IQ Glass)

How Long Will a Kitchen Extension Take?

Project time depends largely on whether you will be extending the property, the type of interior fit-out, and specifications you choose. A single storey kitchen extension, for example, will on average take 12 weeks, however if you are specifying underfloor heating this will add to the time.

(MORE: Get a quote for your new kitchen)

Building Regulations for a Kitchen Extension

Your work will require Building Regulations approval to ensure that the minimum design and construction standards are achieved. These cover all manner of subjects such as fire and other forms of safety, insulation, drainage, electricity and access.

The role of a Building Control officer is to ensure that the minimum standards set out by the Building Regulations have been met. If you are carrying out a kitchen extension, Building Control will need to be notified.

Send a Full Plans application to the local authority, where you pay a fee and the building inspector visits the site at the various stages of the build and inspects the work as it proceeds.

This kitchen extension was built with brick and block for just £80k

The homeowners of this four-bed home created a large open-plan kitchen diner with a kitchen extension that now links the outside in (Image credit: William Goddard)

Don’t get caught out by the Building Regs rule that states that the area of windows, roof windows and glazed doors mustn’t account for more than 25% of the extension’s floor area. 

“The reason for this restriction is simply down to thermal efficiency,” says chartered surveyor, Ian Rock. “Since even quite advanced glazing leaks significantly more heat than the equivalent area of wall, which need to achieve the stipulated minimum U value target of 0.28W/m2K (as covered in Approved Document L1B — Conservation of Fuel and Power of the Building Regs)."

Planning the Layout of Your Kitchen Extension

When planning the layout of your kitchen extension, you will need to keep in mind the basics of what each kitchen requires (fridge freezer, cooker, sink) and then add features around these items.

If you are looking to create a multifunctional space with your kitchen extension, such as an open plan kitchen-diner-living room, zoning the cooking and eating areas will be important. This can be done using furniture and storage.

kitchen extension

(Image credit: IDSystems / scenario / matt clayton photography)

A kitchen island between the work station units and the dining table, for instance, is a perfect break between the separate spaces, and is also a place where you can store pots and pans, and even install a hob and second sink. A breakfast bar can also serve as a way of zoning the kitchen from the dining area.

All of these questions will need answering from the outset so you can ensure your kitchen design meets your requirements.

Introducing Natural Light into a Kitchen Extension


To include a lighting scheme which is practical but also brings the wow-factor in the evenings.

When adding an extension, a lot of your focus and energy will go into making sure the new space is bathed in swathes of natural light. 

But don’t let your enthusiasm run away with you here because there’s a danger of turning the existing space into a less appealing dark and dreary room. 

At the design stage think about where the sunlight falls throughout the day and how you can maximise natural light with the glazing you choose. 

pendant lighting over contemporary kitchen island

Drop-pendant lighting has been used effectively to highlight the kitchen space (Image credit: Original BTC)

Will full width sliding doors be the best option? Could rooflights help bring light deep into the floorplan, and ensure existing rooms still receive daylight?

If your kitchen extension is to the rear of the property, consider bifold doors that open to the garden.The full-height glazing will allow in plenty of sunlight as well as offering views of the outside.

(MOREGreat Glazing Ideas for Your Home)

If you are choosing to add a side-return extension or are after more privacy, then opting for clerestory windows is a good design solution. A bank of rooflights is another popular option as light then penetrates deeper into the space.

Who Do I Need to Build My Kitchen Extension?

Chances are that your kitchen extension will demand some form of structural work and you will need to enlist the services of a designer as well as builders. Once you have chosen a designer, they will draw up plans for the project (to be submitted to the local planning department if your project is going to require approval), and to provide the builders with during the tender process.

When selecting builders to carry out the work:

  • Make sure they come recommended and ask to see previous projects and speak to previous clients for peace of mind.
  • Try to avoid paying day rates.
  • Agree on a fixed price where possible.

You may, however, wish to go down the route of employing a design and build extension company who will be able to handle everything from the design through to the building works and fit-out.

Kitchen with sage green cupboards and large island

This kitchen by Brayer Design features an island unit that doubles as a prepping and cooking area with sociable seating (Image credit: Brayer Design)

Check the Electrics and Plumbing Services Before Building a Kitchen Extension

“One area that’s notoriously prone to cost overruns is supplying the heating, lighting and power,” says surveyor Ian Rock. “It’s fairly common to underestimate how many lights, sockets and taps will ultimately be needed in new extensions, and this can often trigger unbudgeted charges for ‘extras’. 

Often very little thought is given to assessing whether the existing power and heating systems will be up to the job of coping with the additional load, too. Before extending your existing services it’s worth giving them a quick health check.”

  • Electrics: Your electrician will need to check the existing system to see whether rewiring is necessary. They will then return to carry out second fix electrics – such as connections to plug sockets – before the worktops are fitted.
  • You will need to call in a plumber to check the existing pipework is in good condition. You will need to ensure you have both a hot and cold water supply, as well as a waste pump from the sink to the outside. Appliances, such as your washing machine and dishwasher, will also need to be connected to the water supply.

roller blinds from English Blinds in kitchen-diner

A kitchen extension gives you the chance to include lots of windows to let in as much light as possible but if privacy is an issue, factor in blinds, like these roller blinds from English Blinds (Image credit: English Blinds)

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