Kitchen extensions: how much do they cost?

Planning a kitchen extension but don't know where to start when it comes to cost? Our expert tips provide all the information you need to achieve your ideal outcome, while ensuring you set a realistic budget

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When it comes to costing a kitchen extension, you've got lots to think about: not just the budget for the extension itself but the many, many kitchen fittings – and associated fitting costs – too. Of course, a kitchen extension is a great option if you like the idea of open plan living and has the added benefit of increasing the value of your home. But while you may have an idea of how to plan and design your kitchen extension, getting to grips with how much it's going to cost during the planning stage can be trickier. 

When you are setting a budget, there will be a certain amount of flex in each stage, so we have broken the project down into cost areas. As well as build costs and professional fees, don't forget that there may be the cost of applying for planning permission and getting building regulations approval. Finally, you need to budget for the kitchen itself, including flooring and decoration.

Our expert tips provide all the information you need to achieve your ideal kitchen extension, while ensuring you set a realistic budget (and then stick to it). 

How much will building work cost?

You can use our extension cost calculator to get a more exact figure, but as a general rule, plan around £1,500 per m² for building work for a basic single storey extension

A more individual extension, with bespoke windows and doors will cost from £1,900 to £2,200 per m².  Higher specification finishes can increase costs up to £3,000 per m².

Redesigning work, such as reworking an interior layout is likely to cost £500 to £900 per m². A garage conversion will cost £1,000 to £1,250 per m²; cellar conversions, cost from £1,150 to £1,850 per m²; new basement conversions cost between £3,000 and £5,000 per m².

Expect to pay £1,400 to £1,800 per metre for bi-fold doors.

Extra foundation costs will be incurred by difficult ground conditions, such as clay, peat, nearby trees or slopes. Ask a structural engineer (find one at istructe.org) and your local authority building control for an idea of likely foundation type.

Top tip: ‘Small extensions under 15 to 20m² achieve no economies of scale, so costs are higher per square metre,’ says experienced renovator Michael Holmes. 

How much should you expect to pay for professional fees? 

Design fees for a kitchen extension will range from three to seven per cent of the overall build cost, with a minimum of around £2,400 to £3,600 for the planning drawings.

A measured survey of the existing house will cost from £500 to £1,500, depending on the size of the property.

The fee for construction drawings that are sufficient to build from (and for building regulations approval) will typically cost the same as planning drawings, with a minimum of £2,400 to £3,600.

Structural engineer’s fees will range from £500 to £1,000, and are necessary to design the foundations, roof, any large span openings and structural alterations to the existing house.

Find out more about designing single storey extensions in our guide.

How to control building costs

‘Agreeing an all-in rate, plus reasonable expenses and disbursements, gives greater control of costs for planning and construction design,' advises Michael Holmes. 'If the architectural designer is retained to help put the project out to tender and appoint the builder under a formal contract, as well as to provide contract administration services, the fee will typically be a further three to seven per cent of the total contract value. 

For a more ad hoc site attendance, service troubleshooting or adding design detail during the build, it is reasonable to agree a daily or hourly rate.’

How much should you budget to cover the cost of paperwork?

Planning application fees

Planning application fees cost around £200, but what you'll pay will depend on what you are proposing and whether you are in England, Scotland, Wales or Northern Ireland. 

In England, a certificate of lawful development costs £234 (if in Scotland, Wales or NI, ask your local authority). If your extension requires planning permission, you may need the following additional reports:

  • If your project affects trees, a tree report, at a cost of £200 upwards.
  • If your home is within a flood zone, a flood risk assessment: £600 upwards.
  • Many local authorities require an ecology report: from £720 upwards.
  • In areas of archaeological interest, an archaeological report based on a watching brief during excavation: this can cost several thousand pounds.
  • If your home is listed, a historic building report is likely to be required.

Building control fees

Fees for building regulations approval will depend on the size of extension. ‘They are likely to range from £250 for a project of 1-10m² and £900 for 80-100m²,’ says Michael Holmes.

Party walls

A chartered surveyor can arrange party wall agreements for you. ‘This will typically cost from £700 to £1,000 per neighbour,’ says Michael. ‘If your neighbour formally consents to the works, you can avoid having a party wall settlement and save on the fees.’ (See planningportal.gov.uk for details.)

How much will it cost to design a kitchen extension?

Budget from £17 per m² to £144 per m², bearing in mind that costs can be much higher for a bespoke option. The costs of the design work may be included in what you spend on the kitchen itself, or reflected in your total architect fees.

Lighting scheme costs

A scheme from a lighting designer can be well worthwhile. ‘Operate ambient, accent and task lighting on different circuits, for control of zones and the freedom to alter the mood,’ says Luke Thomas, associate at John Cullen, which charges from £102 per hour’s consultation.

Find out how to plan kitchen lighting in our expert guide.

Concrete flooring costs

Polished concrete flooring is on trend and hardwearing. ‘It can be laid both internally and externally, giving spaces impact,’ says Jonathan Reid, director of GreyMatter Concrete. Expect to pay from £120 to £144 per m² for a 50m² 10cm-thick floor.

Find out more about choosing the best kitchen flooring for you in our guide. 

Designer tile costs

Tiles are an excellent way to make a statement. ‘There are so many options, from rustic terracotta to hand-poured encaustic tiles,’ says Harriet Roberts, co-founder of Bert & May, which offers reclaimed tiles, with prices starting from £72 per m².

Have a read of our guide to choosing kitchen tiles for more inspiration.

Heating works costs

‘If you have a relatively new and energy-efficient boiler, check whether it is powerful enough to handle the additional heating demand,’ advises Michael Holmes. ‘If your boiler is more than 10 years old, consider replacing it, as a more energy-efficient design will help offset the cost.’ A straightforward gas boiler replacement will typically cost around £2,300, according to the Energy Saving Trust.

Find out more about heating a kitchen in our guide.

Decorating costs

Wall finishes and painting, including minimal tiling, cost from around £77 per m². The budget for flooring, laid, is usually around £24 to £52 per m².

‘Decorating is one of the easier DIY tasks for those looking to reduce costs of an extension,’ says Michael. ‘Skilled decorators tend to spend more time prepping than painting and this makes all the difference to the finish, so if you plan to decorate, don’t cut corners on sanding, filling, priming and undercoating.’

‘Tiling is a skilled job and, given the high cost of tiles, is not one to complete on a DIY basis unless you have the skill, time and a good quality tile cutter.’ If you think you're up to the job, our guide to tiling a wall is a great starting point.

‘Second-fix carpentry is another good area for the skilled DIYer,’ adds Michael. ‘Laying wooden flooring, hanging doors, installing skirting and architrave and fitting the kitchen itself are achievable tasks. Fitting worktops requires more skill and the correct tools for cutting out sinks.’

Bear in mind your contingency funds

Let’s assume you have set a budget of around £18,000 for an extension measuring 4m x 3m at £1,500 per square metre, plus a new kitchen at £10,000, always add in at least another £2,800 as a 10 per cent contingency should anything unforeseen occur.

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