Approximate costs of building an extension
Short answer
So a two storey extension would cost around £900 per square metre, and so on. Here are some rough price guides for an extension: • Planning application - £462 • Garage conversion - £15,000 • Roofing - £2,000 • Plastering (per room) - £500 • Single storey extension (20 square metres) - £30,000 • Two-storey extension - £37,000 to £100,000.
Longer answer
How much might you expect to pay for a house extension?
House extension costs guide
Extensions are a good way to gain more living space and rejuvenate your home without packing your bags and moving into a new property, but what extension costs are likely to be accrued if you decide to stay put and improve rather than move? The cost of building an extension will depend on the size and complexity of the extension you choose. The average cost of an extension comes in at around £1,000 per square metre for a single storey. If you are having two or three storey extensions, the price will usually decrease according to the number of storeys you are having built.
Single storey and two storey extension costs
Single storey extension prices
A single storey extension is the cheapest sort of way of extending to the rear or the side of your house and will give you living or sleeping space on ground level only. Planning permission may be required depending on the size of the proposed extension and the wok will cost around £25,000. Many people use this sort of extension to give extra living space by enlarging the size of the kitchen or providing another living room or playroom. The exact price will depend on the size and specification of the finished building, and whether or not you want a top of the range, designer kitchen in your new space. If you’ve been considering extending your kitchen, then you’re not alone.
Adding a single storey extension to the back of your house is one of the most popular home improvements, and experts estimate that you can add 5% to 10% to the cost of your house with a great extension. Even if you’ve no plans to move, a kitchen extension can provide you with much-needed additional living space, and the new permitted development rules mean that in many cases, a small kitchen extension won’t need planning permission either.
Building work can be pricey though, so it’s important to think about potential costs before you start making plans. One of the best ways to start thinking about the potential costs of any extension is to work out what size of room you are thinking of building, and then using a cost per square metre to calculate the total bill. The Royal Institute of Chartered Surveyors states that the average cost for a single storey kitchen extension is between £1300 and £1700 per square metre. Under permitted development, you are allowed to extend 3 metres from the existing outside wall of the house, and many kitchen extensions are around 15 square metres. This gives an overall price of between £19,500 and £25,500 for a kitchen extension.
Average costs of single storey extension
A two storey extension would cost around £900 per square metre, and so on. Here are some rough price guides for an extension:
- Planning application - £462
- Garage conversion - £15,000
- Roofing - £2,000
- Plastering (per room) - £500
- Single storey extension (20 square metres) - £20,000
- Two-storey extension - £37,000
Spending a little time to go through your budget will pay dividends in the long run and will help keep your builders focused. 
Adding a single storey extension to the rear or side of the house is one of the best ways of b
oth increasing the available living space, and adding value to your home. A single storey extension could give you an additional bedroom, a playroom, dining room or sitting area. Costs for any type of building work can easily spiral out of control if you have no clear indication of what sorts of costs to expect, so if you are thinking of embarking on a building project, here are some things to consider.
Understanding the average cost for this type of extension will give you a starting point when thinking about budgets, and looking at whether the work you are thinking about will cost more, or less. The industry body for chartered surveyors estimates that the average single storey extension in the UK costs around £1500 per square metre of floor space. This includes foundations, walls, roof, electrical and plumbing work and plastering, but not internal decoration. A 20 square metre extension will therefore cost on average, around £30,000. There are other factors which may increase or decrease this total cost.
What can I do to decrease the cost?
It is possible to cut the costs of a single storey extension, without compromising on the quality of the finish. Decision start at the planning stage. Curves, corners and fancy architectural features are all going to increase the build cost, so stick to as square a shape as possible. If you can use standard sized windows and doors this will help with cost management, and you can reduce costs even further by agreeing to help the builder with basic tasks such as labouring, tiling or putting up coving and skirting boards.
Taking on the project management role on the build will take as much as 20% off the total cost, but will mean you will take on jobs such as working with the Council, buying materials and arranging subcontractors. Think about using reclaimed or salvaged materials wherever possible as these can often be cheaper than buying new, and if you are removing old doors or windows to create the extension, consider selling these on to offset costs.
Factors which will increase extension building costs
Kitting out your new extension can often be the expensive part of the project, and specifying expensive doors, windows, radiators or underfloor heating will boost the cost considerably. Stick to basic items, which are readily available and are competitively priced. Try to be decisive about what you want and stick to your decisions so that you are not incurring extra costs in returning items or having builders unoccupied while waiting for things to be delivered. Always shop around for anything you buy, and don’t be afraid to haggle with builders’ merchants over costs. Planning and legal fees can also quickly mount up, so before getting started speak to the local Council to find out whether your extension falls under planned development rules, or whether you will need to pay for planning permission to be granted. It is essential to take time to choose a good local building firm.
A specialist extension builder will take you through the whole process and will give you a written quotation so you know exactly where you stand. If you are looking to save money on your extension, you could try sourcing the materials yourself. This may be time-consuming, but you will be sure to get the best deals. When budgeting for an extension, be sure to set some aside for any emergencies - you do not want to be left high and dry if anything goes wrong! When you are trying to work out the price of an extension, remember to include the cost of plumbing and electrical work. Other factors, such as the finish, will also affect the cost. If you want tiled walls or floors, these will cost you more money. Watch out for hidden costs like these. You will also pay more for your extension if you live in the south of England.
Other factors affecting costs of building an extension
Here are some other issues that could affect the cost of building an extension: • Ground conditions • Access to the site • Location of the tradesman or extension company. The best way to find a local builder is to use an online directory (preferably with reviews from past customers), such as Top Tradespeople. Remember to ask for quotes from a number of tradesmen to get the best price. A good tradesman will up-front about all the costs for your extension and should take care of any building regulations for you.
Since the credit crunch hit and the banks became more reluctant to lend on property, the house extension business has been booming. Property programmes on TV are less about buying and selling and are more about maximising the space in your existing home, and scaffolding is going up around homes across the country. Extending your property can give valuable extra living space, an extra bedroom or an office, and a professional extension can add as much as 25% to the value of your property too.
Loft or Conservatory extension prices
The cheapest and less disruptive way of extending your property is to convert your loft space into living space, or add a conservatory onto the back or the side of the property. This will cost around £15,000, although if you specify a top of the range finish for your new conservatory or bedroom, it could be a lot more. In many cases you don’t need planning permission to convert a loft or add a conservatory, which means you can get started more quickly and have the job completed in just a few weeks.
Cost of a new kitchen in an extension
If you’re having a new extension built on the side or rear of the house, then it’s natural to want a lovely new kitchen to fill the space. Costs for a new fitted kitchen can also vary enormously. A basic fitted kitchen from a high street store or online retailer will cost you anything between £5000 and £8000. This price may or may not include appliances such as your oven, hob or dishwasher.
If you want a bespoke kitchen built especially for you then the sky is the limit when it comes to pricing, but you can expect to pay upwards of £10,000. Always get any quotes for kitchens and fitting in writing so you can be very clear about what is and is not included, and get quotes from a few local retailers to help you make an effective comparison of the different prices offered.
Two storey extension costs
If you want to add space to both the upstairs and downstairs of your home, then a double storey extension is the best solution as it will give you room to have additional living space downstairs, as well as another bedroom, bathroom or office upstairs. A two storey extension costs 60% more than a single storey extension and the average price for a two storey extension measuring 20 metres square is £45,000. Before setting your heart on one specific type of extension, speak to your builder or project manager and get a range of options so you can see what can be achieved on your budget.
Wooden extension cost
Whatever the style of your main house, wood is one of the most popular materials for a house extension as it blends in perfectly and complements the existing structures. Wood is also a versatile and relatively cheap building material and is suitable whatever the size of the extension being built. Prices do vary, according to the size of the extension and a number of other factors.
Costs of wooden extension design
The first cost incurred when planning a wooden extension for your home is at the design stage. There are several companies which offer pre-fabricated wooden framed extensions which can just be chosen off the pages of a website or catalogue, and if this is the best option for you then there are no design costs at all. At the other end of the scale, hiring a top class architect to design your bespoke extension from scratch could cost several thousands of pounds in architect fees alone. If you opt for a middle ground option, using someone to draw up your plans and getting the approval needed for Planning Permission or building control will cost between £600 and £750.
Wooden extension delivery costs
If you are buying a timber framed extension kit from a retailer rather than having an extension custom made on site, delivery is normally included in the cost of the kit. This is not always the case though and if delivery is not included it can cost around £2,500 to have the kit delivered on the back of an articulated lorry to the building site. Always establish up front what is included and what is not included before committing to buy.
Types of wood will impact prices
Most wooden framed extensions are made from soft woods such as pine, and this is the basis on which prices are set. If however you decide that you want to have your new extension make from another type of wood such as oak or beech then this will double or even treble the overall cost. A good compromise can be to build the frame in the standard pine, and use the more expensive wood for the pieces which can be seen such as the external cladding.
Fixtures and finishing costs
Constructing the basic shell of your extension will cost anything from £15,000 to £30,000 depending on the size, but when preparing a budget you should also factor in the costs for finishing work such as carpeting, adding lighting, decorating and any furniture which you need to buy for the new rooms. Depending on your choices and tastes, this bill could also run into several thousands of pounds.
Costs of paperwork for extensions
If your extension is over a certain size, you will also need to apply for planning permission before starting work. Planning application fees are set centrally and the latest figures can be found on your local council’s website. The average cost for an extension is around £130. Building control warrants and certificates add another cost, and vary between council areas. Fees vary according to the size of the extension being built, but come in on average around £600.
