Get a quote


Understanding Various Types of Extensions and Conversions Cost in the UK

Extending or converting your home can be an exciting prospect, providing you with the extra space you need without the hassle of moving to a new property.

24 October 2023
Default Author image
Eugene Kim

Table of Contents

However, one of the most critical factors to consider when embarking on such a project is the cost. In the United Kingdom, extension building costs can vary significantly based on several factors, including the type of extension or conversion you’re planning. This article aims to provide an overview of the costs associated with different types of extensions and conversions in the UK.

1: Single-Storey Extension
single storey

Single-storey extensions are one of the most popular choices for homeowners looking to increase their living space. They are versatile and can be used to create larger kitchens, dining areas, or additional living rooms. The average cost for a single-storey extension in the UK ranges from £1,200 to £1,700 per square meter. Keep in mind that this cost can vary based on location, materials used, and the complexity of the design.

2: Double-Storey Extension

Modern dormer loft conversion

Double-storey extensions involve adding two levels to your home, often providing bedrooms or additional living space upstairs. These projects are more complex and costly than single-storey extensions. In the UK, you can expect to pay between £1,400 and £2,100 per square meter for a double-storey extension. The final cost depends on various factors, such as the size of the extension and the materials chosen.

3: Loft Conversion

loft conversion richmond
Converting your loft into a usable living space is a cost-effective way to add extra rooms to your home. Loft conversions are generally less expensive than traditional extensions. The average cost for a loft conversion in the UK ranges from £25,000 to £50,000. This cost can vary based on the size of the loft, the type of conversion (e.g., dormer, mansard, or velux), and the level of finish you desire.

4: Garage Conversion

Converting your garage into a living space is another economical option for homeowners. Garage conversions in the UK typically cost between £5,000 and £10,000. The final cost depends on factors like insulation, plumbing, and electrical work. It’s important to note that planning and building regulations may apply to garage conversions, so be sure to check with your local authorities.

5: Basement Conversion

Basement conversions involve converting an existing basement or creating a new one beneath your property. These projects can be more expensive due to excavation and waterproofing requirements. In the UK, basement conversion costs typically range from £1,500 to £3,000 per square meter. The final cost depends on factors like the depth of excavation, the quality of waterproofing, and the intended use of the space.

Factors Affecting Extension Building Costs

Several factors can influence the cost of building extensions and conversions in the UK:

  1. Location: Building costs can vary significantly across different regions of the UK. London and the South East tend to be more expensive, while the North East and North West are typically more budget-friendly.
  1. Size and Complexity: Larger and more complex extensions or conversions will naturally incur higher costs. This includes factors like the design intricacy, structural changes, and the need for custom finishes.
  1. Materials: The choice of materials can have a significant impact on costs. High-end materials and finishes will increase the overall expenditure.
  1. Building Regulations: Compliance with building regulations is essential and may involve additional costs for inspections and modifications.
  1. Professional Fees: Architectural and engineering fees, as well as planning permission costs, should be factored into your budget.


Understanding the costs associated with different types of extensions and conversions is crucial for planning your home improvement project in the UK. While these cost estimates provide a general idea, it’s essential to obtain quotes from local contractors and professionals to get a more accurate picture of your specific project’s expenses. By carefully considering your needs, budget, and the factors that affect costs, you can embark on your extension or conversion project with confidence, knowing you are making informed decisions.

Default Author image


Eugene Kim

Eugene Kim, Founder and Managing Director of Extension Architecture, has led the firm for over 14 years, consistently delivering quality solutions. His dedication has been key to the company's growth and success.

Read next

The latest news, updates and expert views for ambitious, high-achieving and purpose-driven homeowners and property entrepreneurs.

Steph Fanizza, Architectural Design & Team Manager

Tell us about your plan and we'll send you a free quote! It takes less than 60 seconds!

Step 1 of 8

Book a free video meeting