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Kitchen Extensions: Planning, Building Regs, Costs and More

a modern kitchen extension with a glazed section
(Image credit: French + Tye/NOTO Architects)

A kitchen extension is one of the best ways to transform a kitchen from a cramped and awkward space to somewhere that the whole family can use. Modern kitchens aren't confined just to cooking — they're spaces for living, dining, socialising, doing homework, playing and more. 

The rise in popularity of these multi-functional spaces goes hand in hand with a boom in home improvements. Building an extension allows you to create the right proportions for an open plan space that can integrate all these areas into one, after all. 

A kitchen extension is a big project to undertake, no matter what size or style you choose. The cost implications means its important you get your design right too. 

Our complete guide to kitchen extensions covers everything you need to know, from the planning and budgeting of the extension, to what you need to know about a new kitchen design

Kitchen Extension Costs

How Much Does a Kitchen Extension Cost?

Most extension projects cost around £1,500- £2,000 for every square metre of space added. 

Using the example of a 30m2 single storey extension, estimated costs would be between £45,000-£60,000. However, this does not include VAT at 20%. 

This is a general estimation, and that's all you can really expect with no plans for the extension, however, this may help you to work out whether you realistically have the finances in place for a kitchen extension, especially when used in conjunction with an extension cost calculator. The £1,500-£2,000 price, however, is a very good range of pricing based on averages, however, expect to pay a premium in some areas of the south, especially in London. 

The breakdown of these costs may look something like the following:

  • Superstructure (walls and roof): £20,000
  • Kitchen units and worktops: £15,000
  • Flooring: £1,500
  • Electrics including lighting: £3,000
  • Heating and plumbing: £3,000
  • Sliding patio doors: £2,500
  • Decorating and finishing (paint, skirtings, etc): £2,000
  • Associated landscaping works/making good: £2,000 

a corten wrap around kitchen extension with a balcony

A wrap around extension is one that includes both a side extension and a rear extension, maximising the amount of space added.  (Image credit: Andy Stagg)

(MORE: How Much Does a New Kitchen Cost?)

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

  • Party wall agreement: £1,000-£2,000 per affected neighbour
  • Measured surveys: £700-£800
  • Architect fees: Around 7% of construction cost 

Your extension will almost always cost more than you expected it to, so it’s important to have a contingency fund you can fall back on. 

“Allow a contingency of about 20%,” says Jo Dyson, a partner at Mae House Design. “There will always be unforeseen costs no matter how much you plan ahead in advance, especially with old buildings where there are a lot of unknowns.”  

How Much Value Does a Kitchen Extension Add? 

Undoubtedly, the value that a kitchen extension adds to your home depends on the design and how it impacts the use of a home. Overall, you can expect a kitchen extension that creates a larger, open plan kitchen dining space to increase your home’s value by around 5-10%. Data from Rated People estimates that the average increase in house price value from a kitchen extension is £11,514, however, for some properties, it will equate to much more. 

Before working out your budget for a kitchen extension, consult an estate agent about the house price ceiling in your area. 

Is a Kitchen Extension Worth it?  

If you have a small kitchen, a kitchen extension is one of the most valuable areas of your home you can extend to create a more usable space. Incorporating a dining or living space can also help free up room in the rest of your home, which could be used for a home office, for example, with the potential of a domino-effect in freeing up space to rework the layout upstairs too. 

However, a kitchen extension isn’t going to realistically offer you return on your investment due to the high costs of building one, but when looking to increase the volume of space you have available, extending offers value for money in comparison to the fees associated with finding and buying a new house. 

a kitchen extension with large glazed sliding doors

NOTO Architects built this rear extension with a brief to maximise the glazing at the rear of the house, while ensuring the design met Building Regulations for glazing, insulation and drainage.  (Image credit: French + Tye/NOTO Architects)

How can I pay for a Kitchen Extension?

Now that you have a rough idea of how much a kitchen extension might cost, you may be considering how you can finance your project. 

There are several ways you may be able to fund a kitchen extension, including:

  • Using your savings
  • Re-mortgaging your home
  • Credit cards (look for a 0% interest card) 
  • Take out a second mortgage on your home
  • Unsecured loan

Each of these options has its pros and cons, but it's important not to take on more of a financial commitment than you're able to pay back. Failing to pay when refinancing against your home can lead to the bank potentially repossessing your home. 

Will 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 and you may require planning permission

To be covered under PD 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 down internal walls. If you have any doubts, you should check with your local planning department.

(MORE: Side Extension Ideas)

Kitchen Extensions and the Party Wall Act

If you are building an extension, building work involving work to boundary walls between your house and your neighbours needs to comply with the Party Wall Act and, as part of the process, you’ll need to serve a Party Wall Notice to adjoining neighbours. This is notice of the work you intend to do and should be served at least two months before work begins. 

If they consent within 14 days to the work, then you can begin. If they don’t, you and your neighbour will need to appoint a party wall surveyor (this may or may not be the same company) to draft up a party wall ‘award’, which describes how work will proceed. 

(MORE: Building Foundations)

a kitchen extension with a roof lantern and french doors

(Image credit: Westbury Garden Rooms)

What Building Regulations Approval Will I Need for a Kitchen Extension?

How it Works

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.

Your work will require Building Regulations approval to ensure that the minimum design and construction standards are achieved. 

Most kitchen extensions will need to meet a minimum set of technical standards.

These are likely to be:

  • Energy performance
  • Structural integrity as most extensions require foundations 
  • Protection against falls and unsafe walls  
  • Electric and gas safety as most extensions require new systems
  • Fire protection which means ensuring there is safe passage from your home to a safe external area  

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.

Don’t get caught out by the Building Regs rule that states that the area of windows, roof windows and glazed doors must not 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)."

If you wish to create a highly glazed extension, something like a kitchen conservatory extension, you'll need to make a Building Regs application proving that the design won't cause more CO2 emissions than a less glazed version of the design.

What Kitchen Extension Design Should I Choose?

Budget will of course have a bearing on what kind of kitchen extension you opt for. One of the most popular ways to extend a kitchen is to add a single storey addition to the side or rear. And big doesn’t always mean better here. Even extending by as little as 1m or so can really help open up a space, giving you options to remodel the layout so that you can get more out of it. For example, if you choose to add a side extension, this could give you ample room to include a dining area in your kitchen extension without having to eat up lots of outside space.

Consider how the new kitchen extension will link to the existing space and the garden. And note down where the sunlight catches the kitchen throughout the day, too. All these factors will determine where to add your kitchen extension, how big to go and how to glaze it and shade it to prevent overheating (if it’s south facing).

If your budget and outside space allow then building a large rear extension spanning the width of the house could open up lots of possible layouts, while a side return extension can offer a small, but valuable floor plan increase for a kitchen. 

How to Extend a Small Kitchen

As kitchens in older properties tend to be small, these are the most likely candidates for extensions. There are plenty of small kitchen extension ideas around, from large single and double storey extensions to small side return extensions, what you choose will depend on a few factors:

  • How much space do you realistically need in your new kitchen?
  • What is the house price ceiling in your area? What is your budget?
  • How much of your garden are you willing to give up for your extension?
  • What is the layout of the existing home?

The size of the extension isn't necessarily the crux of effectively extending a small kitchen. How you the space and layout functions is far more important. 

Planning the Layout of Your Kitchen Extension

To decide on the layout of your kitchen extension, first you need to ask why you're extending and what you need from the extra space. Is it space for a utility room and downstairs WC? Is it the need for an all inclusive kitchen, diner and living area that you’ll spend most of your time in? Or to create a better connection between your kitchen and outdoor space? 

(MORE: Kitchen Diner Ideas)

Once you've established what you want from the space, time to talk to a designer to make the idea come to life. They'll use your wishlist alongside their expertise to create a space that packs in the most punch for the additional floor space and budget.

the interior of a kitchen with a side return extension

While this side return kitchen extension by Eckford Chong architects only added 5 m2 of extra space, it's transformed the usability of the kitchen area.  (Image credit: Chris Snook)

While many people extend to be able to create a larger open plan kitchen, this isn't the only option available. Broken plan is a riff on open plan spaces, which offers the best elements of an open plan kitchen — light, open sightlines — with the benefits of having more defined areas and divides between spaces, such as less noise and food smells when using physical partitions, or just a sense of a more intimate space when using spatial divides. 

“If you’re thinking of a broken plan space, you can certainly opt for an L-shape, side return or full width extension. Depending on the one you choose, you’ll be able to carve out corners where to place the kitchen, dining table or snug. You can also do this by having different floor heights (for example a sunken living area or raised kitchen) or introducing partitions, such as a freestanding piece of furniture or a bookcase, that will separate the different areas.” 

(MORE: L-Shaped Kitchen Ideas)

kitchen extension island and glazing

This kitchen from Harvey Jones features a large central island, pendant lighting and Crittall style doors leading out onto the garden. (Image credit: Harvey Jones)

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.

“Making design decisions up front can help you keep in control of your budget so you know how much you’ll be spending on flooring, tiling, kitchen units etc,” says Jo Dyson Dyson, a partner at Mae House Design. 

Do I Need an Architect for a Kitchen Extension?

How Much Does an Architect Cost for a Kitchen Extension?

A traditional architect firm will charge between 5-10% of your total budget for the building work. 

Architects are often used for a kitchen extension, especially when the owners are looking for an innovative design, however, it's also possible that a simple kitchen extension can be designed by the likes of a design-and-build company or an architectural technologist

The place to start, therefore, is not so much with the title as the person. You’re after a designer with all the above hard and soft skills. That may well be an architect, but it might just as easily be a local house designer without any formal qualifications. Insurance is key, of course, but many non-architects have that, too. 

(MORE: Find an Architect)

How Long Does a Kitchen Extension Take to Build?

Project time depends largely on large your kitchen extension will, whether you need planning permission or not, the type of interior fit-out, and specifications you choose. A single storey kitchen extension, for example, will on average take 12 weeks to construct, however if you are specifying underfloor heating this will add to the time.

(MORE: Extension Planner)

contemporary kitchen extension

This kitchen extension features lots of glazing to flood the new and existing space with natural light. (Image credit: Harvey Jones)

Glazing for a Kitchen Extension

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. 

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. 

a small and sympathetic side return kitchen extension

(Image credit: James Morris)

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 design. The full-height glazing will allow in plenty of sunlight as well as offering views of the outside.

(MOREGlazing Ideas)

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.

Finding a Builder for Your Kitchen Extension

Whether you’re looking for a reputable builder to bring in his own subbies or sourcing individual trades yourself, personal recommendation is the best way to find a high-quality professional. 

Family, friends and neighbours are a good first port of call when it comes to putting together your long list of potential companies. Failing that, your architect or designer should be able to recommend professionals they have worked with on successful past projects. Websites such as checkatrade.com and ratedpeople.com can also prove a useful mine of information if you’re required to reach out in search of completely new connections.

Once you’ve compiled a list of potential people, contact them for an informal chat about the project. Ask about their range of skills, experience and workload, using the conversation to try and gauge their level of interest in your project. For main contractors in particular, ask if you can speak to previous clients or see past examples of their work to ascertain the quality of the workmanship. 

[MORE: DIY What to leave to the professionals]

a modern kitchen extension

(Image credit: HI-MACS)

Remember, good word of mouth is one of the best forms of advertising in the industry, so happy clients from past projects will often be more than happy to give their builder a plug. Find out if the person is registered as part of a competent persons’ scheme, too, such as the Federation of Master Builders (FMB) for your contractor or the National Federation of Roofing Contractors (NFRC) for roofers, and so on. 

Once you’ve spent plenty of time digging into the details and speaking to various professionals, you’ll be able to begin whittling down the list of people you want to bring onto your project.

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.

(MORE: Find a Builder)

modern kitchen in extension

(Image credit: Brayer Design)

Factoring in Heating and Electrics in Your 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.