How Much Does It Cost To Build An Extension In 2025?

How Much Does It Cost To Build An Extension In 2025? As the construction and home improvement industries continue to evolve, understanding the costs associated with building an extension remains a top priority for homeowners and designers. Factors such as materials, labor, adherence to updated building regulations, and VAT significantly influence the overall budget.

The cost of an extension varies depending on size, style, and complexity. This article outlines average costs in the UK, focusing on four popular types of extensions:

• Single-storey rear extension
• Double-storey rear extension
• Ground-floor wrap-around extension
• Brick porch extension

We’ll provide an overview of total project costs and cost per square metre, concluding with a comparison to help you better understand these expenses.

To create accurate cost estimates, we used a standardized approach across regions, based on these assumptions:

• Extensions have pitched roofs rather than flat.
• Brick or block construction is used instead of timber frames.

Room configurations included in the calculations are as follows:

• Single-storey rear extension: Dining room, utility room, WC.
• Double-storey rear extension: Dining room, utility room, WC, two bedrooms, an en-suite bathroom, a storage room, and a landing.
• Ground-floor wrap-around extension: Dining room, utility room, WC, and boot/cloakroom.
• Brick porch extension: Empty space.

The type of rooms incorporated impacts overall costs. For instance, replacing a dining room with a kitchen involves additional costs for appliances and fittings.

Note: These figures focus solely on extension construction costs and exclude remodeling or refurbishing existing spaces. As such, the total expense depends entirely on project specifics.

To streamline planning, PRG Extensions offers a pricing tool with three finish levels:

• Basic finish: Economical options, e.g., Leyland, Everest, Wickes.
• Standard finish: Mid-range selections, e.g., Dulux, Hamilton, Slim Line.
• Premium finish: High-end choices, e.g., Farrow & Ball, Fine Line, Siemens.

We based our estimates on standard finishes. Contractor pricing benchmarks vary by company size and specialization:

• Lower range: Smaller companies offering lower costs with limited specialization, ideal for basic to mid-range projects on a budget.
• Mid-range: Medium-sized firms balancing affordability with expertise, suitable for most mid-range projects.
• Higher range: Larger companies with higher costs, offering extensive specialization and robust project management for complex tasks.

Average Costs for Common Extension Types

Here’s a table showing the average building costs of a single-storey rear extension with a gross external area of 30 square metres:

Key Insights:

• Building in London costs 21% more than in other regions.
• Minimum cost: £65,568; Maximum cost: £102,408.

Single-Storey Rear Extension

For a 30-square-metre single-storey rear extension:

• Insights: Costs in London are approximately 21% higher than other regions, with total expenses ranging from £65,568 to £102,408.

Double-Storey Rear Extension

For a 60-square-metre double-storey rear extension:

• Insights: Costs range from £114,540 to £179,281.

Ground-Floor Wrap-Around Extension

For a 35-square-metre wrap-around extension:

• Insights: Total costs range from £78,096 to £122,056.

Here’s a table showing the average building costs of a ground-floor wrap-around extension with a gross external area of 35 square metres:

Key Insights:

• Minimum cost: £78,096; Maximum cost: £122,056.

Based on these examples, average construction costs (using mid-range contractors) are as follows:

• Single-storey rear extension: £78,186 (£2,606 per square metre).
• Double-storey rear extension: £136,525 (£2,275 per square metre).
• Ground-floor wrap-around extension: £93,064 (£2,585 per square metre).
• Brick porch: £6,569 (£1,314 per square metre).

Larger projects often benefit from economies of scale, reducing the cost per square metre. These estimates exclude VAT and provide a foundation for planning your next extension with PRG Extensions.

Use our ball park calculator to get a view of the cost for your up and coming project