The cost to extend a house varies widely depending on factors such as the type of extension, size, materials, design complexity, and location. Here is a summary of typical costs based on recent 2025 data:
Cost Per Square Meter (or Foot)
- Single-storey extension:
- UK: £1,700 to £2,400 per m² (approx. $1,900 to $2,700 per m²)
- Canada/US: $200 to $500 per square foot (~$2,150 to $5,400 per m²)
- Two-storey extension:
- UK: About 50% more than single-storey, roughly £2,400 to £3,600 per m²
- Canada/US: $360 to $480 per square foot (~$3,875 to $5,165 per m²) for ground floor; second floor slightly cheaper
- Basement extension:
- UK: £2,000 to £3,500 per m²
- Loft conversion:
- UK: £1,200 to £2,500 per m²
Typical Total Costs by Extension Size and Type (UK)
- Small extension (~20 m²): £40,000 to £56,000
- Medium extension (~30 m²): £60,000 to £84,000
- Large extension (~50 m²): £100,000 to £140,000
- Two-storey extension (~60 m²): £108,000 to £180,000
- First-floor extension over garage (~25 m²): £45,000 to £75,000
Other Considerations
- Quality of finish affects cost significantly; basic finishes may cost £1,000 to £1,700 per m², while high-end finishes can go up to £2,200 per m²
- Additional costs include planning permission, architect fees, building regulations, excavation, heating/AC, bathrooms, kitchens, and furnishing
- Shell-only extensions (external structure only) cost less, around £1,200 to £1,700 per m², useful if you plan to complete interior work yourself
- Location impacts cost; for example, London can be much more expensive than other regions
Summary
For budgeting, a typical single-storey house extension in the UK can cost between £1,900 and £2,400 per square metre, with total project costs ranging from tens of thousands to over £100,000 depending on size and complexity. Two- storey extensions and basement conversions are more expensive. In North America, costs are generally quoted per square foot and range from $200 to $500+ per square foot depending on extension type and finish quality
. Planning for contingencies and obtaining multiple quotes from vetted builders is recommended to avoid surprises and ensure quality workmanship.
