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How much does it cost for a loft conversion and house extension in the UK?"

Loft Conversions

Basic Loft Conversion:

  • Cost: £15,000 - £20,000

  • Details: This typically includes a simple room conversion with basic insulation, flooring, and windows.

Dormer Loft Conversion:

  • Cost: £30,000 - £50,000

  • Details: Adds a dormer window to increase headroom and usable space. Includes more extensive structural changes, insulation, and possibly an en-suite bathroom.

Hip to Gable Loft Conversion:

  • Cost: £40,000 - £60,000

  • Details: Converts the sloped side of the roof to a vertical gable end, increasing space. Involves significant structural work and is often combined with a dormer.

Mansard Loft Conversion:

  • Cost: £45,000 - £70,000

  • Details: Changes the roof structure to create a flat roof and vertical walls, maximizing space. This is the most extensive and expensive type of loft conversion.

House Extensions

Single-Storey Extension:

  • Cost: £20,000 - £50,000

  • Details: Adds a single floor of additional space, typically used for extending kitchens or living rooms. Costs vary based on size and finish.

Double-Storey Extension:

  • Cost: £40,000 - £100,000

  • Details: Adds two floors of additional space. Offers more room but requires more extensive structural work and planning permission.

Side Return Extension:

  • Cost: £20,000 - £45,000

  • Details: Utilizes the narrow space at the side of a property. Commonly used in terraced houses to extend kitchens or living spaces.

Wrap Around Extension:

  • Cost: £50,000 - £100,000

  • Details: Combines side and rear extensions, creating a larger and more open plan living area. Involves significant work and planning.

Factors Influencing Costs

  1. Location: Costs in London and the Southeast are generally higher than in other parts of the UK.

  2. Size and Complexity: Larger and more complex projects cost more.

  3. Quality of Materials: Higher-end finishes and materials increase costs.

  4. Professional Fees: Architect, planning permission, and building regulation fees add to the total cost.

  5. Builder's Fees: Labour costs vary depending on the contractor's experience and location.

Additional Considerations

  • Planning Permission: Check if you need planning permission for your project.

  • Building Regulations: Ensure your project complies with building regulations for safety and structural integrity.

  • Hidden Costs: Budget for unexpected costs that may arise during the project.


  • Loft Conversion: £15,000 - £70,000 depending on the type and complexity.

  • House Extension: £20,000 - £100,000 depending on the size and type.

These estimates provide a general idea of costs, but it's essential to get detailed quotes from professionals based on your specific project requirements.

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