Kitchen extensions – how to design, plan and cost your dream space

Create space for your dream kitchen by designing a kitchen extension. Our step-by-step guide takes you from budget and brief to build.

If you dream of a large, open-plan kitchen, but don’t want to move home to get one, a kitchen extension could be just the solution you’re looking for. Not only will an extension give you the extra room you desire and better flow of space, it could also add value to your home.

A kitchen extension is a big job, so thorough planning is key. But don't worry – we're here to guide you on exactly what steps to think about when you plan a kitchen extension. And, just as importantly, the order in which to tackle them.

Starting from scratch? Read: How to plan a kitchen – your step-by-step guide to the perfect space

1. Make initial plans

kitchen with white walls wooden flooring dinning table with chair kitchen platform

(Image credit: Future PLC/Simon Whitmore)

The kitchen layout needs to be decided early on so that all of the electrical and plumbing services can be positioned to suit your plan. Think about what you want from your extension, and therefore how much space you want your extension to provide. Do you need room for a kitchen-diner? Do you want to include a kitchen island?

Ensure your new extension will provide an adequate supply of natural light. It may not be possible to add windows to a side extension, so glass roofing may be a good option. You want your extension to add space to your home... but not space that's dark and uninviting.

The cost of a kitchen extension

It is important to consider your overall budget. Architecture firm 2pm Architects predicts that you can expect to pay around £1250 per sq m for a low-cost single storey extension with budget fittings and specification, and no site constraints. This figure roughly doubles to £2500 for a more complex structure with luxury features.

Take this number and add at least 10 per cent as a contingency to cover any unforeseen costs.

2. Choose an architect

Once you’ve decided on a style and space, look for an architect or designer who will be able to advise you on what’s possible, guide you through the planning process and help you work on a budget. Make sure your architect is RIBA Chartered and make use of recommendations from family and friends.

Ideally, you should create a shortlist of three or four architects. Ask to see examples of their previous work and to speak with former clients. Your chosen architect will then undertake a site survey and present plans to you for approval.

3. Understand building regulations and planning permission

exterior of house garden brick wall of house with white windowa

(Image credit: Future PLC/David Giles)

Once you have approved the architect’s plans, you will know whether the extension falls under permitted development, or if you will need to apply for permission. Your architect should be able to advise you in this respect, but for more advice about planning permission, visit GOV.UK (opens in new tab).

Under permitted development, you will still need to obtain building regulations approval from a building control officer (BCO), also known as a building inspector. Building regulations apply to most work and ensure safety and energy efficiency. You can choose between a local authority inspector or private approved one, which may be quicker.

If you’re applying for planning permission and your house isn’t listed or subject to restrictions, your architect can submit the plans for you. Allow at least eight to ten weeks for the application to be processed. You may also require approval under the ‘Party Wall’ Act, which is a wall that stands on either side of a boundary of land belonging to two or more owners. Works with foundations within certain distances of the walls also fall within the act, not just work to the wall itself.

Need more ideas? READ: Kitchen extension ideas that will open up your space

A single-storey rear extension is usually the most planning permission-friendly option, often achievable under permitted development. Don’t swallow up too much garden otherwise you risk reducing your property’s value. A simple side extension that’s subservient to the main house is also planner-friendly and can widen a narrow kitchen without stealing precious garden.

Side-return extensions are a common choice for terraced properties, which often have a half-width kitchen tacked onto the rear. The section of garden to the side of the kitchen is called the side-return and can be utilised to create a kitchen the full width of the property. A side-return can create valuable wall space for cupboards and worktops. And it can still be light filled, provided you install a series of skylights in the new roof space.

4. Find a builder

When looking for a builder, try recommendations from friends and family. You could also post a job on Ratedpeople (opens in new tab). Your architect should also be able to suggest contractors they’ve worked with before. As with choosing an architect, make sure to get references and check that they have relevant insurances and guarantees.

Make sure any builders you request quotes from are TrustMark approved. This means their previous work will have been vetted and subjected to on-site inspections to check it's up to Government-approved standards.

Costs vary for building works, and it is a good idea to get several quotes. Allow at least three weeks for contractors to prepare their prices, as they themselves are relying on sub-contractors to price parts. Then ask them to submit a proposed schedule.

5. Consult a kitchen designer

white tiles with mosaic tiles and white plate

(Image credit: Future PLC/Dominic Blackmore)

This can happen at around the same time you are deciding on a builder. Your architect may have planned the basic layout of the kitchen for you, but now's the time to take your architectural drawings to your favourite kitchen companies. They can then fine-tune the layout and come up with designs for your approval.

Layout finalised and supplier chosen, you'll then be able to ask for detailed layout, wiring and plumbing plans. Have these ready to share with your builder in time for the next step...

Get it right: Kitchen lighting – everything you need to know

6. Get started on site

Once you have planning approval, Party Wall Agreement and a kitchen is on order, the building work can begin. At this point, 'first fix' decisions, such as the position of walls, floors, ceilings, electrics and water pipes should have been finalised.

While preliminary works get under way, ‘second-fix’ design decisions and a tender can be made about finishes, light fittings and tiling. Allow plenty of time for flooring to be ordered.

You’ll need a contract with your builder and your architect can advise you on the type required. ‘Most contracts require staged payments against valuations,’ says Hugo Tugman, founder of Architect Your Home. ‘This means that your architect visits the project every payment period and issues a certificate to say what percentage of the total work is complete. You then pay against completed works.’

7. Final stages

kitchen with dinning table with chair and white wall with kitchen platform

(Image credit: TBC)

Once the building work is finished, any snagging issues can be dealt with. Snagging refers to the knock-on structural and finish effects of the building settling back on its foundations after the work is completed. Only when these have been done to your satisfaction should you make your last payment to your builder in return for a final certificate. Make sure that all electrical work, plumbing and gas supplies are signed off, too.

Chosen your floor? Kitchen flooring – everything you need to know

Before your kitchen cabinetry and appliances can be installed, you’ll need to lay your flooring. Fitting of your new kitchen should then take up to four weeks. After the cabinets have been fitted, your kitchen company will template the worktops, which should take around two weeks. In the meantime, you can paint the walls and add fixtures and lighting. Then, once the worktops are in place, you’re done!