How Much Does a Home Extension Cost? Price per m2

The price of a home extension can vary due to a number of factors, and this process may seem daunting at first sight. The cost of building an extension will notably depend on the type of extension, quality of materials, your location, and the professionals you hire, among other factors. Here’s a guide to help you understand how much you can expect to pay, as well as what to expect the process to involve. 

Factors in the Cost of an Extension

In general, for the average cost of a single-storey extension in the UK you can expect to pay between £1,200 (for a basic extension such as a conservatory) and £2,500 per square metre, and potentially more if you live somewhere such as London for example. As with any building project, this price depends on a number of factors. Naturally, the first of these to consider is quality - if you opt for premium materials for a high-quality finish, expect to pay 40% more than you would for basic quality materials. Design quality is also an important consideration not to be overlooked. 

The use for your future extension will also play a role in the cost. If your extension project includes adding or remodelling a bathroom or kitchen, the cost factors will also include expenses for fixtures, appliances and fittings, as well as plumbing and electrics services. You can generally expect to pay an additional £5,000 - £10,000 to add a bathroom for example, and even more to outfit a kitchen. Size can also make a difference: if you are building a particularly large extension, the economies of scale will have an effect, and you will find that the price per unit area begins to decrease. Consider this when planning the size of your extension, as you may find that a larger extension is more cost-effective than you thought.

Types of Extension

The cost of your extension will also depend on your property and what type of extension you choose to build. One cost-effective solution to increase your living space is to add a double storey extension. The construction of a two-storey extension doesn’t change the price considerably compared to a single-storey extension, since the most expensive aspects of the construction (namely the foundations and the roof) remain the same regardless of how many stories the extension will be. The main additional costs to figure in will be due to materials and labour. As a general rule, to estimate the cost of a two-storey extension, you can expect to add around 50% to the price of a sing-storey extension. Of course, double storey extensions are often more complex and can be more difficult to obtain planning permission for, so the best choice will depend on your specific property and situation. 

Building an extension over a garage or existing single-storey structure can also be acost-effective route, as long as the foundations are already sufficient. A basement extension is another option, but due to their complexity the cost per square metre will be higher than a traditional extension: digging a new basement will likely cost around £2,000 to £4,000 per m2. A conversion of an existing basement or cellar space will be significantly lower of course, especially if no excavation is required. Lastly, a loft conversion is a popular way to extend your home and add more living space. The cost of a loft conversion can also vary widely depending on what type of loft conversion you choose, as well as factors such as how much alteration is required to the existing roof structure, and the quality of materials and finishings.

Location and Site

The cost of a home extension will also vary depending on your geographical location within the UK - your home improvement project will be significantly more expensive if it is located in London or the South-East of England. In London for example, the cost of a single-storey home extension can often range from around £2,000 to upwards of £3,000 per m2 for a high-end finish. In northern England, Wales and Scotland you can expect the project to cost less, although prices may also be higher if you’re close to a large city. When considering the cost of your extension, it is important to balance the price of the extension with the value it will add to the house. Consider the ceiling price for your postcode before committing to construct an extension; otherwise, you run the risk of finding yourself out of pocket when the work has been completed, especially if you are carrying out the extension with the goal of reselling the property for a profit. 

In addition to your property’s location, there are other aspects of the build that can have an influence on the final price. One factor to take into account, which is outside of your control, is the soil type on the plot of land where the extension is to be built. Certain types of soil require more preparatory work than others, which leads to the cost of the foundations being elevated in relation to other types of terrain. Your project may also be more complex if your property is located in a designated or protected area, such as an AONB, historic town centre or conservation area, or if your home is a listed building. These types of circumstances may require bringing in experts or obtaining additional permissions for your project, which will need to be factored into the cost as well.

Managing Your Extension Project

Your own level of involvement in the project will also have an impact on the eventual cost. Naturally, the more of your own time and expertise you can lend to the build, the less you will pay others. If you have the time and skills to carry out most of the work yourself, you can potentially save up to 40% with a DIY extension compared to the price of hiring a main contractor to manage the project on your behalf. You can also choose to manage the project yourself and directly hire builders and tradespeople to complete the work, or hire both a main contractor and subcontractors, to reduce your own involvement. For many homeowners, the simplest option is to hire an architect who also offers project management services to handle the project from start to finish.

Do you need an architect for an extension?

Even if you decide to manage your own project, engaging the services of a registered architect for your extension project is highly recommended. Despite the initial expense of an architect’s fees, you will almost invariably find that a qualified architect will save you money in the long run. In addition to walking you through your project, from planning permissions to construction, an architect will be able to use their expertise and training to make the most out of the space you give them to work with and find optimal solutions to your brief. They will also be able to offer their creativity to bring even the most complex designs from paper into reality. In addition, buildings designed by architects will be more energy-efficient and constructed to a higher standard. This will lead to lower energy and maintenance bills in the future, as well as being kinder to the environment. 

Hiring an architect also offers the advantage of allowing you to get a far more precise cost estimate. As you can imagine, having an exact quote can help you avoid paying an unfair price for the extension. Your architect will make sure that you aren’t being overcharged, and will be able to source the material suppliers and contractors who will be able to give you the best value for your money. They will also be able to advise you regarding reclaiming VAT, since some types of extension are eligible for VAT relief. 

Planning Your Extension Project

Once you have considered the financial aspects of the build, you can begin to plan out in more detail what the extension will look like. Decide how large you would like the extension to be, as well as what it will be used for. Depending on the size of the extension, you may find that you require planning permission. This is one of the first aspects of the extension to consider, as in many cases you will require this before the project can commence. For some smaller extensions (those enlarging the property by less than 8m in length towards the rear) you may not require planning permission. However, in some cases, this permitted development does not apply, for example if you live in an area deemed an “area of natural beauty” by the conservation authorities. 

After the design of your extension, the next step is to decide which construction professionals will work with you on the project, if you choose to manage hiring subcontractors yourself. The goal is to find a group of local builders and tradesmen who will be able to deliver a good quality result at a fair and affordable price. You can find builders via your friends and family, who will be able to let you know about builders they have previously used that have a good reputation in the local area. Once this has been arranged, there is nothing left to do but let the professionals you have hired get on with the project. During this period, you may choose to stay with friends and family or rent a place to live during the duration of the construction project.

Do you have a home extension project? Search and compare local architects in your area on find-my-architect.com to find the right extension expert near you.