Planning a kitchen extension: the ultimate guide

Planning a kitchen extension? If I told you that we are now spending twice as much time thinking about home improvements than we did before lockdown, what would you think? Is that you? Are you constantly looking around your home and thinking this or that could be better? If you’ve realised that your kitchen is a bit too small for what you need or you’ve decided you’re ready to go open plan (or broken plan), planning a kitchen extension may just be your solution to getting those vital extra square metres and maximise your plot, plus it’s a chance to rework your interior layout, too.

OK, I admit it: planning a kitchen extension is rather a large home improvement. It’s way more than a new lick of paint or new pieces of furniture, so requires precision planning. But as well as finding that we’re spending double the time thinking about improving our homes, a study of 2,000 Brits by Independent Network powered by VEKA, found that we’re spending an average of eight hours and 21 minutes a month making their residences perfect – that’s up from four hours and 44 minutes pre-lockdown. Woah.

To be honest, this is music to my ears as I firmly believe that the best home renovations come from hours/days spent planning and scrutinising what you want to achieve and why, plus what you’d like it to look like by the end. Plan, plan, plan I say (I’m a fan of a spreadsheet, which I’m sure the rest of Team These Three Rooms would happily attest to).

To help you along with your kitchen extension planning, I worked with Jill Morgan and Charlotte Luxford, who both write for Kitchens Bedrooms & Bathrooms magazine (the print side of These Three Rooms) to come up with some tips. Here goes…

1. Create a wishlist

The first thing to consider when planning a kitchen extension is how you’ll spend your time in it, what’s possible for the space and how you can use it most efficiently.

Assess your existing room, noting the elements you want to keep as well as any bugbears. Then write a wishlist, prioritising your key items. This may be things such as an island, large patio doors and lots of glazing, a larder or utility room. A better link to the garden and more natural light are reasons we hear often, too.

Think about your interiors style, too – do you want a streamlined look? This usually involves integrated appliances and floor-to-ceiling cabinets. Or want more of an eclectic appearance? This usually has a more relaxed feel might mean a large vintage dresser takes centre stage.

You should make a list of the key essentials you want in your kitchen – the ones you cannot live without. Place them in order of preference and give this list to your chosen kitchen designer.

Be realistic and take the opportunity to get rid of any features or products (I’m thinking those gadgets in the back of the cupboard) that you never use, even with the best intentions. Think carefully and deeply and note everything down – likes and dislikes. It’ll be a handy reference throughout the project if you begin to doubt anything, too.

2. Set a budget

Charlotte asked Ben Burbidge of Kitchen Makers By Burbidge for his top budgeting tips when planning a kitchen extension. He said: “Be realistic about what you can achieve and the structural work involved, as adding roof lights, changing entrances, moving pipes and rewiring will make it more expensive.” So think about the extent of work you think you’ll need and whether you’re planning to relocate the kitchen and its plumbing or can work with the layout as it is.

Don’t forget to budget for planning permission and building regulations approval. A single-storey extension will usually cost between £1200 to £3000 per sq m, depending on the level of finish, plus always set aside a 10% contingency.

Want to keep costs down? Choosing standard building materials and regular fittings for key items such as glazing can help save money.

Of course, you’ll need to budget for the kitchen itself, too. If your dream design is out of reach, consider
buying a used or ex-display kitchen from suppliers including The Used Kitchen Company or Used Kitchen Exchange. Do remember that finishes including marble worktops or parquet flooring will mean a large investment, so best to factor these in from the start of your planning.

Bespoke isn’t always the most expensive either – sometimes local cabinet makers can create your desired look for less and take in your exact needs and work to the money available. See our Close to Home initiative to find your local, independent design specialists.

3. Find out if you need planning permission

Sounds boring, yes. But crucial, absolutely. With any project that impacts on your home’s outside space, you may require planning permission from your local council. If you do require it, looking to see what work has been done in your street can indicate as to whether your plans will be approved – valid excuse to be a nosy neighbour.

planning a kitchen extension
This 3 x 3m rear extension was covered under permitted development rules. The construction was overseen by Plus Rooms and extension designed by architects The Art of Building. Photography: Fine House Photography.

If someone down the road has had a kitchen extension, this may signal that you’ll be able to do the same. Maybe give them a knock and find out what their project was like and how the planning permission process was for their project. However, even if your street is full of new extensions, best to check in with the council about your home – there may be different rules depending on your home’s location, property type or proximity to next door, for example.

The good news is that many modest kitchen extensions fall within permitted development. This is where you’re able to build without the need for formal planning permission up to a certain size depending on your property type and whether it’s been remodelled before. Although it’s a good idea to seek Prior Approval for peace of mind.

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Check out guidelines online: lists all you need to know for England and Wales. For Scotland, head to

Remember, your home’s permitted development allowance will depend on where in the UK you are as well as if it has been previously developed. If you live in a conservation area, an Area of Oustanding Natural Beauty, or in a listed building, you’ll likely face stricter terms for planning, too.

Also check out your local Building Control, as an inspector will be required to ensure your project meets Building Regulations.

Watch The Kitchen Sessions: Plan your perfect kitchen extension

4. Decide on the type of kitchen extension

This is largely dictated by the size and shape of the available outside space and by what’s allowed by the council. The most common type of kitchen extension is a single-storey one to the back of the house, or a side-return extension which is popular on Victorian terraced houses – filling in the narrow space that projects from the back (usually where the bins are kept, right?).

The homeowners had been living in their ground-floor flat within a Victorian villa in Clapton, east London for several years before they decided to renovate it. They replaced a dilapidated glass conservatory with a striking extension designed by Scenario Architecture. As the property is located within a conservation area, the new addition had to be sensitive to the original layout. This was achieved by keeping the original rear wall of the house intact, using its window and door openings to create internal balconies, and cladding the exterior in sustainably sourced timber. Photography: Matt Clayton.

You can combine the two types to form a wrap-around extension, forming an L-shaped addition, which could help boost space inside and square off a room. The aim of all: create more space, so your perfect kitchen can be sited within it, along with a dining area or living area (or both) should you wish.

When you’re planning a kitchen extension, always keep in mind what sort of kitchen style you’re after, what’s on your wishlist, whether you want an island, etc, as these elements should factor into the extension design as well as the kitchen design. Think in tandem: kitchen and extension together.

This will not only help keep your vision clear, but also help you decide on where to put things such as windows, doors, plug sockets and light switches.

planning a kitchen extension
Martins Camisuli Architects’s brief was to expand this period property from a two-bedroom house into a modern three-bedroom home for a busy family. The owners wanted an open-plan kitchen-living-diner and an ensuite to the master bedroom above. The building’s back was demolished and rebuilt, with a side and rear extension added. Photography: Alex Macguire.

5. Plan the kitchen early and find a designer

I told you my motto is ‘plan, plan, plan’ and it really is true for a large project like a kitchen extension. The more you can plan before any work begins, the better.

So when you’re planning a kitchen extension and looking around for builders and architects (ask friends and family for recommendations, or seek them out via verified trade bodies), engage with a kitchen designer too, even if only just starting out.

Don’t only rely on your architect’s concepts for the space – now’s the time to start shopping around for a kitchen and use free consultations so you can cherry pick the best ideas.

They will work with your builder or architect to get the most from the plans. Plus, they’ll help build a picture of how you will use your kitchen and come up with the best, most creative and cost-effective way to make this a reality.

“It’s really important to design your kitchen before or during the planning stages of your extension,” Sophie Randall at John Lewis of Hungerford said. “If you approach a kitchen designer once planning permission has been granted, you risk not having the space for the scheme you really want.”

Make your designer aware if you’ve got a very specific look in mind (cue wishlist) or whether there are any existing elements you’d like to keep and incorporate. Ensure they have a vision for the whole space and ideas for how the kitchen will connect with the other areas, such as dining, living and working zones.

Then establish exactly what services your chosen company offers and whether you want them involved at the design stage only or later in the process. Initial meetings are often free of charge, followed by a fee of a few hundred pounds to take the design further, which is offset against the kitchen. For an all-inclusive service, expect around 10% of the total cost.

The owners of this end-of-terrace Victorian house were after a contemporary extension. Inside the large 30sq m addition, architects at Gruff delivered beautifully designed zones including a kitchen and dining area, a quiet reading alcove, and a sunken lounge (shown below). Both the decking and external fireplace encourage entertaining and relaxation long into the summer nights. Photography: Ben Blossom.
planning a kitchen extension

A kitchen designer will also be able to work with you and your other trades (think of them as your dream team) to suggest best layout, materials and how to create good flow from the kitchen to other areas of the kitchen extension, through to outdoors, too.

Simon Taylor, managing director at Simon Taylor Furniture, made an interesting point: “A glazed wall or bi-folding doors allow plenty of natural light to flow into the space so I wouldn’t recommend having a timber or even hand-painted kitchen in this space, as the light would fade the furniture over time.” Little nuggets of information like this are invaluable to a good kitchen extension project, I reckon.

6. Think about your kitchen layout

When planning a kitchen extension and deciding how much room you need for the actual kitchen, look at your storage needs and assess whether you require the same or more units, and how that translates into floor and wall space, as well as the size and type of cupboards and drawers.

For good flow, it’s leave 1 – 1.2m clearance around and between your units, which can have a big impact on your design, especially if you want an island.

I asked Jayne Everett, design director at Naked Kitchens for her best starting point. “The all-important working triangle,” she said. “Keep the path between your sink, fridge, and hob clear to make cooking much simpler. Don’t try to squeeze in more or larger units if there’s no space, as it will make the room feel small and cramped.” Roger that.

Natural illumination and glazing will also dictate your layout. Ideally, you should locate the kitchen in the darkest part of the room, relying on downlights and task lighting to brighten it, with living and dining areas nearest the garden so they can benefit from the sun and indoor-outdoor link. Remember to factor in the orientation of your property, too.

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It was important to use as little garden space as possible for this kitchen extension project by Inter Urban Studios. A large amount of glazing ensures the kitchen-diner stays as light as possible. The use of fins adds drama to the scheme, while also adding a certain amount of privacy from their neighbours.

The perfect kitchen layout features the things you really need and want, rather than lots of clutter. Your belongings will also dictate how much and the type of storage required, so don’t be surprised if a kitchen designer asks you lots of questions when you have a design consultation.

Ask yourself: how many people use the kitchen? Do you need to dine in the space? Is there a back door that’s in constant use? You might even like to draft a layout you think might work and then measure up to ensure it will fit before you have an appointment.

7. Assemble your dream team and go to tender

Armed with your technical drawings, get in touch with at least three contractors for quotes. Costs can vary widely, depending on how busy the builder is, what other work they have in your area, and how much they want to get the job.

It’s not always as straightforward as picking the middle-of-the-road quote either. Follow your instincts, as there also needs to be an element of chemistry between you – positive communication is essential.

Speaking of trades and your ‘dream team’, “who can I get to manage the project?” is a popular question. You can project manage yourself if you’re diligent and organised, and happy to arrange delivery of materials in line with the construction schedule. Or, architects and many construction companies offer a design and build service, while independent project managers and kitchen designers all have their specialisms and roles to play.

Ultimately, it’s up to you, your budget and the complexity of the project to determine who you engage.

If you do project manage yourself, I recommend a very good, detailed spreadsheet!

planning a kitchen extension
Although the existing kitchen was already on a split level, Martins Camisuli dug down further to create more height. The steps were also relocated to the right of the room for better access. Photography: Alex Macguire.

8. Set a timeline

With your builder hired and a date set for starting on site, contact your kitchen designer to place your order and arrange a time for delivery. The average extension takes 12 to 14 weeks, but a large project can take anywhere up to six months or a year.

Similarly, the lead time for you cabinetry can be as long as 12 weeks. Some companies will require you to have an otherwise finished room – with flooring, electrics and plumbing in place – prior to installation, so it pays to plan ahead
and have a detailed timeline in place.

9. Blend old and new

No one wants a kitchen extension that doesn’t flow with the rest of the house, right? The aim: perfect flow.

Keeping structural details such as the ceiling and floor heights the same between old and new rooms has a huge impact on integrating the new space, but there are other ways of blurring the boundaries too.

Replicate the style of skirting boards, internal doors, and window frames in the new space and keep to the same flooring and wall colour throughout for continuity.

Many kitchen companies are happy to design and install coordinating storage, fire surrounds, and media units to tie open-plan living areas together.

This 3 x 3m rear extension was covered under permitted development rules. The construction was overseen by Plus Rooms and extension designed by architects The Art of Building. Photography: Fine House Photography.

10. Get ready for the project to begin

Ok, you’ve assembled your team, decided on the type of extension and figured out if it’s allowed by the council, plus you’ve got your dream kitchen planned and ordered. How do you keep it all running smoothly so the end result is perfect with a capital P?

Before it all kicks off, you’ll need to notify Building Control as well as your neighbours that work is about to commence (get in their good books).

Make sure there’s good access and parking; a skip and portaloo are ordered if needed; you’ve set up a temporary kitchen; and arranged any storage hire or accommodation if you’re moving out.

Make sure you know where things such as the stop cock to turn off the water supply and the mains box for the electrics are.

Have all your belongings packed away before builders arrive – but leave the kettle out (!) – and consider how long you won’t have access to cooking and washing up facilities.

Don’t forget renovations insurance, too, to make sure you’ve covered.

And finally…stay one step ahead

While groundworks are taking place, make your second-fix decisions, which usually happen around week 12. Finalise your lighting plan and positioning of power points with both your builder and your kitchen designer, and start sourcing big-ticket items such as furniture, surfaces and flooring.

Windows and doors will be made to order, and companies tend not to manufacture them until the space is
measurable – so there’s often a lull while you wait for glazing to arrive.

Agree a realistic fitting timescale with your installers and if you are using several different trades check when each will be needed during the process.

Planning a kitchen extension? Now all that’s left is to look at our gallery of 10 amazing kitchen extensions – inspiration awaits.

Featured image: An initial application for this wraparound kitchen extension was not approved by Lambeth council, as it would have changed the property too much. The original property was L-shaped and the extension plans would have completely changed its proportions. After the application was refused, the homeowners considered appealing at first – but it was never pursued as architects at The Art of Building came up with alternative option.

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