It’s not surprising if you need some more space at your home but don’t want to move. Fortunately, a house extension is a perfect way to add some extra space to the place you already live in. Whether you want to extend your kitchen, add space to your current family room, or increase the size of your garden, a house extension will help you do that in a cost-effective way. House extensions are also a great choice if you do not wish to relocate. This is especially true if your kids’ school is nearby or if your workplace isn’t far away.
Nonetheless, planning an extension is challenging. You might be interested in how its cost compares to relocating. In this post, we’ll look at house extension costs and any additional costs that may arise. So, if you love where you live, want to add value to your existing home, or want to avoid the inconvenience of relocating, this post will prove to be very helpful.
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House Building Costs UK
Before you get to know about the house extension costs, you must consider certain variables. For instance, you need to determine the size of the extension, the materials to be used, fittings’ quality, glazing volume, the complexity of the design, area per square foot and much more. Without even taking into account the additional costs, such as planning approval, engineer fees, and surveys, a number of factors will affect the final cost.
Still, a house extension is usually cheaper than purchasing and relocating to a bigger home. Moreover, a good extension can add more value to your living space. Most of the extension projects will cost around £1,000/m2 to £2000/m2 for a small to medium single-storey internal space. The entire cost of the extension, however, might range from £25,000 to £37,500 if it covers a 20m2 area. And, if you’re planning to do home extensions of about 30m2, the cost may range between £40,500 to £67,500.
An extension of a single-storey building varies in cost little from an extension of a double-storey building. This is because, with a double-storey extension, the costly structural work is already done, and the project will only need one roof and one foundation. However, combining two-storey and single-storey extensions will obviously cost twice as much given the increase in square footage. To give you an estimate, we’ve calculated the extension costs according to the type of home extensions and the extension size. Have a look at the following home extension cost breakdown in the UK:
| Type of Extension | Size of Extension (m2) | Estimated extension cost |
| Single storey extension | 20 | £25,000 to £37,500 |
| Double-storey extension | 40 | £40,500 to £67,500 |
| Bathroom extension | 9 | £20,000 to £25,000 |
| Kitchen extension | 20 | £35,000 to £50,000 |
| Conservatory extension | 20 | £20,000 to £27,000 |
| Glass box extension | 15 | £45,000 to £60,000 |
| Utility room extension | 7 | £10,000 to £13,000 |
| Orangery extension | 16 | £20,000 to £50,000 |
| Garage extension | 15 | £4,500 to £20,000 |
| Multi-Storey extension | 20 per floor | £20,000 to £25,000 per floor |
| Wrap Around Extension | 20 | £25,000 to £40,000 |
You must also include the extra expenditures for the planning approval, architect, engineer, and surveyor in addition to these extension charges. These professional fees can make up around 10 to 15% of the extension costs. Plus, if you live in London or near it, you must estimate 20% to 30% more per square foot as project costs.
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Factors That Affect Extension Costs
The cost will depend on several factors, no matter what type of extension you’re going for. Following are the factors that will contribute to the total extension costs:
- The soil type can affect construction costs because it determines the way the foundation will be constructed. A good soil stack will save you money, whereas soil that is difficult to extend will cost you more.
- Most of the cost will go into the roof and the foundation, which are the two most important parts of an extension process. So, no matter how many storeys you’re going to extend, the size of the extension will primarily affect the total cost.
- The purpose of the extension is also a contributing factor. For instance, if you’re going for a kitchen or bathroom extension, you may have to pay more. This is because these extensions need specialised fittings as compared to a family room.
- Glazing also affects the extension cost. The amount of glazing and the type of glazing will greatly affect the total cost. If you’re going for picture windows, bifold doors, conservatories, or orangeries, know that they are more expensive than simple double-glazed windows.
- The labour costs add to the total extension costs. If you live in a place where all the materials need to be shipped, it will be more costly. Moreover, labour costs are higher than 25% per square foot in and around London so consider that too.
- You won’t need a project manager if you’re supervising the home extension yourself. However, if you need a project manager with knowledge of UK construction regulations and the ability to arrange materials, you’ll need to pay for the services.
- Some additional costs like planning permission costs will also come into play. These are enforced by the local council and will determine the type of materials used and the construction methods required.
Single Storey and Rear Extension
Mostly, people choose to do a single-storey and rear extension. It improves your house’s layout and also adds to its value. You can extend your house’s entire breadth or width through this type of extension. Some people decide to add another ground floor on the side of their house or go for a wrap-around or L-shape extension. The extension cost for a basic single-storey ranges from £1000 to £2000/m2. However, the prices will also vary according to the fittings used and other factors we discussed earlier. This is an essential extension, and the cost will increase if you add specialised fittings for your bathrooms or kitchen.
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Double Storey Extension
Two-story extensions involve two floors and are suitable if you need more square footage. They are also a good idea if you need larger versions of the same family room in your house. The cost per square foot for the two-storey extension will be a bit expensive, but the roof and foundations will remain the same. You can estimate it to cost about 1.5 to 1.75 times that of a single-storey extension. Therefore, with this type of extension, you’re just adding walls, floor joists, and extra interior finishes and fixtures.
Kitchen Extension
Aside from the extra fittings and fixtures, a kitchen extension will cost the same amount per square foot as a family room extension. For instance, a kitchen requires drainage, an extractor fan for ventilation, electric supplies, mains gas, and hot and cold water. Besides that, for a modern kitchen design, you’ll need countertops, cabinets, storage cupboards, and built-in appliances like an electric stove and ovens too. So, if you’re going for a modern kitchen extension, you must add £10,000 or more to the extension cost per square foot to cater for the extras.
Bathroom Extension
A bathroom extension also resembles a kitchen extension as it also requires fittings and fixtures. You won’t need mains gas for a bathroom, but you’ll need hot and cold water, a bathtub, a wash basin, a shower, and a toilet pan. If you’re planning to go for a modern bathroom, you’ll need a central heating boiler and cupboards. Besides that, the basic requirements for the bathroom include drainage and plumbing services. The bathroom extension can be a part of the single-storey extension, or if you want it upstairs, you can also go for the double-storey extension. For the bathroom extension, prepare to add £5000 more per square foot to the total extension cost depending on the extras you add to the bathroom suite.
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Glassbox Extension
A glass box extension is a conservatory extension but doesn’t involve metal supports. It includes glass beams and units, and its structure is included in the house’s layout within the thermal envelope of the living space. However, a conservatory is considered an exterior part and has a separate external door leading to it. Thus, for a glass box extension, you must consider the regulations for ventilation, heating, and overall thermal performance.
Orangery Extension
An orangery is considered a hybrid between a standard room and a conservatory. It consists of brick-built pillars and a raised roof. It serves the purpose of natural lighting for a particular space. This type of extension has a glass roof covering less than 75% of the total roof area and glass walls surrounding less than 50% of the overall wall area. The cost of an orangery extension will be less per square metre than the standard cost of an extension. However, it might be more expensive than an equally sized conservatory because it needs more building materials.
Conservatory Extension
Adding a conservatory to your place is a perfect way to add more space so that you have extra room for entertainment and relaxation. The conservatory extension costs depend on various factors, which include style, materials, roof, and dwarf walls. There are different types of roof styles which include Victorian, Georgian, and Edwardian, or you can go for a mix of these. The cost of an extension for a conservatory can range from £5000 for a cheap one to as high as £40,000 for a high-end conservatory.
Utility Room Extension
A utility room can help you do the unsightly home chores such as laundry and cleaning. The cost of an extension for a utility room factors in the roof, walls, groundworks, foundations, doors and windows, drainage, flooring, plastered ceiling and walls, and first-fix electrics and plumbing. Moreover, some additional costs include final finishes such as light fittings, furniture, appliances, switches, cupboards, worktops, and more. Consequently, the cost of such an extension will be around £10,000 or more depending on the type of roof or flooring you choose.
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Multi-Storey Extension
A multi-storey extension is a bit complex because of the local planning authority regulations. Various planning regulations make it difficult to do a multi-storey extension. Thus, it is important to discuss the extension project with the local planning department to know their opinion on the matter. This is because the local planners don’t want the houses to look larger than other houses in the locality. Since most homes in the area are two stories, you are not allowed to construct anything higher than the roofs of the neighbourhood’s existing homes. Thus, a two-storey extension is the most you can do with a multi-storey extension.
Wrap-Around or L-Shaped Extension
A wrap-around or L-shaped extension is a rear addition used to utilise the back portion of your house. Hence, a wrap-around extension will be a good choice if your home has a lot of alleyway space. Keep in mind, however, that a wrap-around extension is more costly compared to the rear or side extension because of the structural work involved. If you’re planning an extension of 45m2, the project costs will be around £75,000 to £145,000 in London and around £60,000 to £120,000 outside London.
Garage Extension
A garage extension also adds value to your property and it’s a cost-effective idea for parking vehicles and dumping extra clutter from your home. In the UK, there are standard sizes for building new single attached garages, which are as follows:
- Small-sized garages: 2.4m X 4.9m
- Medium-sized garages: 2.7m X 5.5m
- Large-sized garages: 3m X 6.1m
Likewise, the cost of a garage extension depends on what type of extension you choose, such as a prefabricated concrete structure, a metal structure, a wooden structure, or a brick structure. The average associated costs of a garage extension can range from £5000 to £16,000.
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Extension Cost Factors
In the above sections, we discussed the cost of building and materials. However, other costs also add to the average costs of extension. These include the labour costs and the costs of engineers, surveyors, architects, and more. We have compiled a list of services and their estimated cost to give you an idea. Below the table, we have discussed all these extension costs in detail.
| Job/Service | Description Of Service | Estimated Cost |
| Structural engineer | Perform inspection on sagging roofs, foundation problems, load-bearing walls, or sliding chimneys. | 3% to 7% of the total extension cost |
| Surveyor | Calculates dimensions, layout, planning, drawing constructions | 3% to 7% of the total extension cost |
| Architect | Make plans and layouts according to planning permission. Also prepares bill of material quantities | 3% to 7% of the total extension cost |
| Planning Fee | Charged by the planning department | The planning department determines this, but it’s around £200 to £300 |
| Tree Report | Identifies any trees that have preservation order in or around the property | Around £800 |
| Flood Risk Assessment | Determines any flood risks | Around £800 |
| Ecology & archaeological report | Determines if there are any ecology or archaeological sites of particular interest | Around £1000 |
| A bricklayer or builder | Makes concrete slabs, does the brickwork and foundation work | £150 to £250/day |
| plasterer | Plastering walls and roofs and putting floor screed | £140 to £170/day |
| electrician | Install fittings, sockets, electrical cables, and heating controls | £150 to £280/day |
| plumber | Install gas, heat, and water fittings | £150 to £280/day |
| roofer | Make roof tiles, roof covering and leadwork | £150 to £230/day |
| painter | Painting and decoration of the interior and exterior property | £100 to £180/day |
| carpenter | Makes doors, windows, structural timbers, and frames | £140 to £180/day |
Structural Engineer
The cost of hiring an engineer depends on the size of the extension. Plus, sometimes the extension involves removing the walls, which must be replaced by brickwork piers supporting the lintels. An engineer must work in accordance with the UK Building Regulations and provide detailed reports on calculations that the architect can use later. The engineer’s main task is calculating the load on foundations, the foundation’s depth, and the concrete’s thickness.
Surveyor
A qualified surveyor will advise on planning and construction regulations and if you need any approvals or planning permission. A surveyor will conduct a site survey and take measurements and photographs of the area to be extended. Surveyors start working from the Ordnance Survey points of known altitude and coordinates. They work through these points to determine the position and elevation of your extension compared to other properties.
Architect
After taking data from the engineer and the surveyor, an architect plans suitable for the application. An architect also liaises with the local authority and acts as a project manager during construction. In most cases, an architect represents you (the client) and discusses matters with the building trades and local authorities.
Planning Fee
As a client, you have to pay the local authority after the architect has submitted the details. These are the admin costs that include regulations and planning permission. The building Regulations include standards for materials, design, artistry and more. Planning permission determines whether the house extension complies with the local authority.
Tree Report
A tree report includes information about the trees in and around your property. A professional arborist makes the tree report, which is necessary for carrying out an extension. The arborist also determines if a tree has to be removed and whether the tree to be removed is a protected species or not.
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Flood Risk Assessment
Click to Get QuotesFlood risk assessment is necessary for determining whether the property has a risk of being flooded or not. Sometimes a surveyor can do this work too, but if you hire a flood risk specialist, you’ll have to pay him separately.
Ecology and Archaeological Report
An ecology and archaeological report are produced to determine if the extension will affect any site with archaeological importance. Plus, it also determines if the extension will impact the ecology.
A general builder or bricklayer
A general builder or bricklayer clears the site and levelling the ground before the foundation is laid. He also carries out the insertion of sewer, pouring concrete foundations, and landing drain pipes.
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Carpenter
A carpenter performs the woodwork, which includes making doors, windows, frames, structural roof rafters and more. The woodwork is done before and after the plastering work.
Plumber
A plumber installs gas and water pipes before plastering, and the second fix includes installing sinks, water heaters, radiators, and bathroom suites.
Plasterer
A plasterer provides a finishing touch to the roof and walls. He can also install plasterboard and exterior plastering, including spreading cement mortar for waterproofing.
Electrician
An electrician also performs his duty in the first and second fix. The electrician performs the first fix before plastering, including installing cables and wires behind the walls and roof and below the floorboards. The second fix includes installing switches, light fittings, power points etc.
Roofer
A roofer creates breathable and waterproof fabric for the structural roof timber and might also install the leadwork for weatherproofing purposes. A roofer does roofing as soon as the interior structure is dry.
Painter and Decorator
The painter and decorator is the last person to do the job for the extension process. The job of a painter and decorator is to give a finish to the surfaces in the house and make them more attractive.
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UK Planning Permissions & Building Regulations: Guidelines
Besides all the house extension costs for your living space, your project will largely depend on the UK Planning Permission And Building Regulations. Following are the details of these commissions in regard to your house extension:
Planning Permission
Since some types of construction projects might not be in accordance with the UK Planning permission, you must contact the department to save money and time. Some exemptions come under the category of ‘Permitted Development Rights, which you must follow. These permitted developments also depend on where you live in the UK. Besides that, there are a few restrictions that which you must consider for all types of extensions, which are as follows:
- House extension should not be more than half area of your total existing house area.
- Extension must not be higher than your highest existing roof
- The principal elevation’s building line must not be crossed
- The height of the eaves must not be higher than 3m if the extension is within the boundary of 2m
- The extension eaves must not be higher than the existing eaves
Moreover, if the extension goes beyond the side elevation of your existing space, it must not exceed 4m in height. Plus, it should be a single storey and must not be more than half the width of your existing property.
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Building Regulations
Any addition per square foot to your property must be in accordance with the Regulations. The Regulations for home extension include foundations, external walls, internal walls, roof, drainage, electrics, and kitchens and bathrooms.
FAQs Regarding House Extensions
1. Can I build my extension?
Yes, you can build your extension if you’re willing to save money. However, that will require a lot of effort. Plus, you’ll need to do everything from scratch and require many skills and expertise. You’ll have to do the job of an engineer, an architect, a surveyor, and the list goes on. If you’re planning to cut down on labour costs, you can do specific jobs yourself, but still, it’s very difficult to do everything on your own.
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2. Can I extend the front of my house?
You cannot extend the front of your house according to the Permitted Development regulations. However, if your house front is at a good distance from the public road, you can contact the local planning authority to discuss and request permission.
3. Is home extension cheaper than rebuilding?
It is cheaper to extend and renovate your house as compared to demolishing and rebuilding. Moreover, if you need extra space by adding an extra room or kitchen, you don’t need to destroy your existing property and rebuild it.
4. How much does the foundation cost for a home extension?
The foundation costs vary according to the type of soil and other factors. These factors include depth to the subsoil, the height of the water table, the type of foundation, and the size and weight of the extension. According to an estimate, the foundation costs lie between £100 and £130 per metre square. The foundation cost also includes removal of soil, excavation, and ready-mix concrete.
Get Extension Quotes
How much should you be quoting for your home extension? Before an extension, it’s difficult to get a detailed estimate because it’s still early in the process. An estimate is a guess that is based on the information available, and it can increase when the project is discussed in detail later. Engaging with a professional surveyor can help you determine estimates and save money in the long term. Additionally, it’s advisable to compare the costs by getting 3 or 4 quotes before determining the final price.
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