The Cost Of Building An Extension

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The cost of building an extension on your house

The Cost Of Building An Extension In The UK

As experienced UK property experts, we understand that one of the most frequently asked questions by homeowners considering an extension is how much it will cost. The cost of an extension can vary widely based on a variety of factors, including the type of extension, the size, the materials used, and the location of the property.

In this comprehensive guide, we’ll provide you with a breakdown of the costs associated with building an extension on your house, along with tips and advice to help you plan and budget for your project.

Image showing a house with an extension on one end
If you use higher quality materials then the cost of building an extension can increase dramatically. Photo © Roger Templeman (cc-by-sa/2.0)

Factors Affecting the Cost of an Extension


Before we dive into the specifics of the cost breakdown, let’s take a closer look at some of the key factors that can impact the overall cost of your extension.

Type of Extension: There are a variety of different types of extensions to consider, including single-storey, double-storey, and wrap-around extensions. Each type of extension comes with its own set of costs, which will need to be factored into your budget.

Size of the Extension: The size of your extension will obviously play a large role in determining the final cost. Larger extensions will require more materials and labor, which can significantly impact the budget.

Materials Used: The materials you choose for your extension will also affect the overall cost. For example, if you opt for high-end materials like granite or marble, you can expect to pay significantly more than if you choose more affordable options like wood or vinyl.

Location of the Property: The location of your property can also impact the cost of an extension. Factors like access to the site, the need for planning permission, and the local cost of labor and materials can all influence the final price.

Photo of a house with a small extension on one end
Costs of building an extension can be quite low if the extension is for a simple utility room. Photo © Roger Templeman (cc-by-sa/2.0)

Cost Breakdown for an Extension

Now that we’ve covered some of the key factors that can impact the cost of your extension, let’s take a closer look at the cost breakdown for building a single-storey extension on a typical UK property.

Design and Planning: The design and planning stage of your project will typically cost around £1,500 to £3,000. This includes architectural drawings, planning permission, and building regulations approval.

Site Preparation: Site preparation can include tasks like excavation, demolition, and site clearance. Depending on the size of your extension and the condition of your property, you can expect to pay around £2,500 to £5,000 for site preparation.

Foundations and Groundwork: The cost of foundations and groundwork will vary depending on the size and type of your extension. For a single-storey extension, you can expect to pay around £8,000 to £15,000 for foundations and groundwork.

Shell and Structure: The shell and structure of your extension will typically account for around 25% to 30% of the overall cost. This includes materials like bricks, mortar, and roofing, as well as the cost of labor. For a single-storey extension, you can expect to pay around £20,000 to £40,000 for the shell and structure.

Windows and Doors: The cost of windows and doors for your extension will depend on the size and type of materials you choose. On average, you can expect to pay around £4,000 to £8,000 for windows and doors.

Interior Fittings and Finishes: Interior fittings and finishes can include items like plumbing, electrical, and heating systems, as well as flooring and decorations. Depending on the size and scope of your project, you can expect to pay somewhere around £8,000 to £20,000 for interior fittings and finishes.

Total Cost: Based on the breakdown above, the total cost for a single-storey extension on a typical UK property can range from £45,000 to £90,000.

Keep in mind that these figures are estimates, and the actual cost of your project may vary depending on a variety of factors. For example, if you choose high-end materials or opt for a more complex design, your overall cost may be higher than the estimates provided.

Image showing a small brick extension
House extensions can be cost effective and blend in perfectly with the main building. Photo © Roger Templeman (cc-by-sa/2.0)

Tips for Planning and Budgeting for Your Extension


Now that we’ve covered the cost breakdown for a single-storey extension, let’s discuss some tips and advice for planning and budgeting for your house extension project.

  • Set a Realistic Budget: Before you start any work on your extension, it’s important to set a realistic budget. Make sure to take into account all the costs associated with the project, including design and planning, site preparation, materials, and labour.
  • Choose a Reputable Builder: One of the most important decisions you’ll make when building an extension is choosing the right builder. Make sure to do your research and choose a reputable builder with a track record of success.
  • Consider the Return on Investment: An extension can be a great way to add value to your property, but it’s important to consider the return on investment before you start your project. Research the local property market and make sure your extension will add value to your home.
  • Plan Ahead: Planning ahead is key to a successful extension project. Make sure to plan every detail of your project in advance, including the design, materials, and timeline.
  • Be Flexible: Despite careful planning, unexpected issues can arise during any building project. It’s important to be flexible and prepared to make changes as needed to ensure the success of your project.

Important: Make sure to get multiple quotes for costs and references for any builder before they begin building an extension on your property.

Photo of a grade II listed property with an extension.
if you own a listed property, such as this Grade II listed building, make sure you have correct planning permission before beginning any building work. Photo © Alan Murray-Rust (cc-by-sa/2.0)

Conclusion: Be Realistic About The Cost Of Your Extension

Building an extension can be an exciting and rewarding project for any homeowner, but it’s important to be realistic about the costs and requirements involved.

By following the tips and advice provided in this guide, you’ll be better equipped to plan and budget for your extension, and ensure a successful outcome for your project. Remember to choose a reputable builder, plan ahead, and be flexible, and you’ll be well on your way to a beautiful and functional new addition to your home.

Reducing The Cost Of Building An Extension


There are number of ways to reduce the costs of building an extension on your house. A simple design with either a rectangle or square shape will be cheaper than one with curves and corners. Basic fittings for flooring and fixtures like kitchen units can also keep costs down. You can always upgrade these later.

If you are capable you can also reduce the cost of building an extension by doing labouring, painting and other types of work yourself. This can result in significant savings if you are able to do the work. Discuss these ideas with your builder and see if you can reduce the cost of the building work.

Photo of a house with a high quality extension
When done properly an extension on house can blend in seamlessly. This extension turned the house from three to six bedrooms. Photo © David Hawgood (cc-by-sa/2.0)

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