Kitchen Extensions: Beginner’s Guide to Planning a Kitchen Extension

Want to extend your kitchen to create a new functional zone that will become the heart of your home? From layouts to heating options and costs, here’s what you need to know to ensure your kitchen extension project is a success
by Emily Batesmith
6th December 2023

Thinking about expanding your home with a kitchen extension? Many recent trends when it comes to home improvement involve transforming the kitchen into an open-plan social zone, often extending outwards to create a kitchen-living-dining space that accommodates the whole family at all times of day.

In the past, homes would feature as many rooms as possible in a home, each with their own distinct purpose. But we live in more informal times, where busy lifestyles require multifunctional spaces that cater for the needs of many.

We’re spending so much more time in these rooms – relaxing, dining and entertaining, as well as cooking – and we want a kitchen that’s streamlined, uncluttered yet still homely, with everything functioning perfectly. So, it’s no surprise that many of us want to transform our homes with a kitchen extension, expanding this space, adding value and creating a better connection with the garden through glazed sliding or bifold doors.

Where’s the Best Location for a Kitchen Extension?

The perfect solution to achieve a kitchen-diner or kitchen-living space in many existing buildings is to extend to the rear, sometimes as part of a wider renovation to rejig the entire downstairs layout to better suit modern life.

And whether you want to build a contemporary glass-box or a traditional addition that blends into the original structure, adding a kitchen-diner extension is an easy way to generate extra living space whilst also adding value to your property. By building outwards to create your kitchen extension, you can link areas together and create a bigger, more open zone that will make everyday living more enjoyable.

More Advice: Open Plan Living Ideas & Advice for Kitchen, Living & Dining Rooms

Kitchen Extension: Beginner's Guide to Planning Your New Kitchen Addition

This home has been upgraded with a structurally-impressive glazed kitchen extension, designed by Scenario Architecture. The addition makes use of steel beams that span the width of the house. Each beam and column is finished with compact insulation to avoid thermal bridging whilst keeping a slender profile. Photo: Matt Clayton

If you have a small garden, then a small side-return could provide sufficient space for a kitchen extension with a dining table and seating. However, the most common type of kitchen extension is a single-storey addition to the rear that, budget allowing, spans the width of your home. If the room is to work at its best, decisions such as the position of glazing, plumbing, electrics and ventilation (scroll down) should be planned hand-in-hand with the architectural process.

It’ll be important to establish a firm idea of how your kitchen extension is going to be laid out and where the appliances, sockets and lighting should go. Other fittings and specifics such as kitchen style, colour, materials and fittings such as kitchen worktops should come later.

Planning the New Kitchen Extension

A kitchen extension is a major investment, so before diving in you must consider what you want to achieve from the extra space it provides.

Think about how often you will make use of the room, what exactly it will be utilised for and the overall style you want to establish. For example, ask yourself whether your cooking habits will require an elaborate setup, how many people will you be cooking for and how much space you need for appliances, and so on. Shape the design around your answers.

Consider future demands, too – what you need right now will be different to what you want 10 years down the line. For example, can you easily convert the children’s homework or play area zone into a space for adults to relax in when the space is no longer required?

Bear in mind that creating any sort of extension is no mean feat, so it’s a good idea to get professional design advice from the outset. An architect or design and build company will be able to translate your requirements into a perfectly-tailored scheme.

Learn More: Who Should Design My House Extension?

Kitchen Extension: Beginner's Guide to Planning Your New Kitchen Addition

This dilapidated Victorian house has been welcomed into the twenty-first century with a new side-return kitchen extension, masterminded by Oliver Leech Architects. It features exposed Dougals fir timber, plaster walls, brushed copper worktops and polished concrete flooring

A kitchen designer or your architect can work through the optimum layout for the new room, balancing how much space should be allotted to the various functions, whether you’re a keen cook who needs loads of cupboards and drawers for storage or you need entertaining space to have dinner parties for a dozen friends.

If the extension means that kitchen straddles both old and new areas of the house, you may have to work around RSJs that will interfere with a straight run of wall units. A good designer will make it all look as seamless as possible. This will probably be the largest room in your home, so it’s essential that functionality isn’t lost.

Ensure that your plan accounts for the basic requirements – is there easy access to the garden? Have you allowed for adequate storage? Is there space for a washing machine and dishwasher, or will you have a separate utility room?

Every kitchen extension’s layout will be different, just as every property has its own quirks, but these basic elements are essential.

CLOSER LOOK How Much Does an Extension Cost?

Factors such as the size and how open-plan you want your space to be (which will dictate any requirement for supporting steels etc) are among the biggest contributors to the total cost of your extension. According to Tamsin Bryant of ABL3 Architects, the average extension her firm works on costs around £2,500-£3,500 per m², subject to complexity and finishes.

“Structural complexity, the types of foundations required, any existing services and whether you’re building over a public sewer will also impact on your total budget,” says Tamsin. But perhaps the biggest variable will be the specification: high-quality bespoke kitchens or top-of-the-range glazed doors don’t come cheap, but they will add real wow factor to your finished project.

Where in the country you’re building will also weigh in on the cost of your extension as labour rates differ significantly across the UK. “A side return or wraparound extension on a terraced property in London would typically cost between £80,000-£100,000 to take it to a builder’s finish,” says James Bernard, director of Plus Rooms.

Read More: Kitchen Design & Costs: How Much Does it Cost to Design & Fit a Kitchen?

Getting the Kitchen Extension’s Layout Right

For most people the kitchen itself will be the important aspect, so select its location and layout wisely. It’s a good idea to position it where there’s most available wall space – too many windows or doors will limit the layout possibilities.

Also make sure the kitchen isn’t a thoroughfare, which can be annoying at best and hazardous at worst – imagine children running past while you’re dealing with hot pots and pans.

Working triangle rules still apply to an open-plan kitchen – you should never be more than a few steps away from the fridge, oven, sink and prep area. Ideally you shouldn’t have to walk around your island or other pieces of furniture to access them. Account for movement requirements, too, don’t just try and cram fixtures together if you don’t have sufficient room.

Kitchen Extension: Beginner's Guide to Planning Your New Kitchen Addition

Crown Imperial‘s Furore kitchen range offers a striking glossy appearance and handleless design. The scheme  can be specified in a wide range of colours to perfectly match your new kitchen extension

The space between a run of kitchen cabinets and an island should be at least 1m, for example, and if you want a breakfast bar, stools will need at least 1.25m behind them. Try to retain a feeling of space, which is why you’re extending in the first place.

For example, if you’ve invested in lots of glazing to make the most of great views of the garden, then keep sightlines open from the moment you step in the room rather than blocking them with a kitchen peninsula.

More Ideas: Kitchen Extension Ideas: 20 Inspiring Designs

Heating, Lighting & Ventilation for Kitchen Extensions

Whatever type of kitchen extension you create, you’ll have to factor in the essentials: heating, lighting and ventilation.

Heating options

Warming an open-plan kitchen extension presents particular challenges – you may have limited wall space and face the issue of fluctuating temperatures. The best option in this case is underfloor heating (UFH), which will create an even spread of warmth throughout the room and free up walls for cabinets and furniture. The most efficient choice of underfloor heating is a wet system, which will have plastic pipework running deep under the floor to the boiler.

The other possibility is a dry setup that comprises a network of electrically-heated wires that sit below the floor covering. This can operate independently of the main central heating system, which is handy.

Natural light

One of the benefits of having an open-plan kitchen-diner is that you are not sacrificing natural light by having smaller enclosed rooms.

In most cases, rear extensions will include some sort of full-height glazing – be it bifolds, French doors or sliding units – which provide easy access to the garden and create an even flow of light.

Rooflights or lanterns set within a flat roof construction can be used to drench the zone in sunshine, allowing brightness to filter through to the rest of the property. Glass roofs on side returns will have similar effect.

Kitchen Extension: Beginner's Guide to Planning Your New Kitchen Addition

For those seeking the appearance of traditional-style steel doors but requiring modern thermal and security performance, IDSystems’ Heritage Doors offer the ideal alternative. The glazed Heritage Doors are manufactured from thermally-broken aluminium with a polyamide thermal break between the inside and outside of the frame

Ambient & task lighting

In addition to natural light, an artificial lighting scheme should be planned from the outset. You’ll need a mix of general ceiling lamps to illuminate the entire zone and task lighting for specific jobs, such as preparing food or working on a laptop.

You may want to feature a pendant fixture over the dining table or island unit to add an interesting focal point.

Spotlights over your work surfaces will provide good visibility while you’re cooking and under-cupboard lamps will add ambience and background illumination.

Ventilating your kitchen extension

You must also consider ventilation at an early stage in your project – you’ll usually have some sort of upholstery in a kitchen-diner, so you don’t want cooking smells to linger. There are numerous practicalities to consider for your ventilation unit, such as the power required, noise level, where it will be positioned and whether you want a ducted or recirculation model.

There are plenty of choices to suit your interiors, from sleek ceiling-mounted versions and feature pendant designs to professional down-drafters.

Extractors vary hugely in price. Ducted versions pass the air through pipes and remove it from your house – great for dealing with smoke and smells. Recirculation models channel the air through a filter and, as the name suggests, recirculate it back into the room. These are less effective than ducted versions, but are cheaper and easier to fit.

Kitchen Extension: Beginner's Guide to Planning Your New Kitchen Addition

Extending into the side return has enabled a spacious kitchen-living zone in this Victorian terrace house project by architectural practice CAN. Photo by Jim Stephenson

Common Issues with a Kitchen Extension

A lack of walls for kitchen cupboards can be an issue in open-plan extensions, and washing machines, dryers and sinks are easier to fit against external walls, compounding the problem.

If that is the case for you, “we would usually recommend floor-to-ceiling cabinetry, or incorporating a kitchen island into your design,” says Sean O’Donnell, who is a kitchen designer with bespoke furniture company Burlanes.

“Islands not only provide additional storage, but extra worktop space too, as well as a breakfast bar and somewhere for the family to gather and sit, eat and socialise. Bespoke kitchen islands can be made up to 3m long and can also house integrated appliances.”

Kitchen Extension: Beginner's Guide to Planning Your New Kitchen Addition

Gruff Architects transformed this Victorian home with a new, contemporary kitchen-diner extension. Light floods the extension through arched and pill-shaped glazing – by IQ Glass – which references the home’s period design details. Photo: FRENCH + TYE

A general lack of space for all the functions required is common. “If you want to cook, dine and lounge in your new room, be clever,” says Amy Conn, a designer from kitchen and furniture company Neptune.

“Swap a large dining table for a kitchen island with a breakfast bar, or build in bench seating around a small table, which will free up space for a sofa, too. Or maybe you could downsize your utility room into a couple of floor-to-ceiling cupboards in your kitchen. These will still hide away the washing machine, tumble dryer and all your cleaning bits and bobs.”

Essential Advice: Structural Options & Considerations for a Home Extension: Your Complete Guide

This article was originally published in September 2021 and has been updated in December 2023.

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