One of the most desirable improvements to add to your home is a kitchen extension. And, although not cheap, it can be a cost effective way of re-configuring and adding space – and value – to your house.
Building work costs
Plan around £1,500 per m² for building work for a basic 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.
- 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.
Controlling 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.’
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.
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.)
Kitchen design costs
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.
Concrete flooring costs
Polished concrete 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.
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.
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.
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.’
‘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.’