One of the most common questions we hear is: 'How much will my extension cost?' The honest answer is that it depends — but we can give you realistic London benchmarks for 2025.
Typical Cost Ranges
- Single-storey rear extension: £50,000 – £100,000+
- Double-storey extension: £100,000 – £200,000+
- Side return infill: £40,000 – £70,000
- Wrap-around extension: £80,000 – £150,000+
These figures cover construction costs only. Professional fees for architects, structural engineers, and planning consultants are agreed individually at the outset of each project.
What Affects the Price?
- Size and complexity of the build
- Ground conditions and foundation type required
- Party wall obligations
- Specification and finishes chosen
- Access constraints on terraced or mid-terrace properties
The Structural Engineer's Role
Structural engineering is an essential part of any extension project — covering the design of foundations, steelwork, and the production of Building Regulations drawings. Each project is priced individually following a review of your drawings and the specific technical requirements.
Need help with your project?
Our engineers are ready to discuss your requirements.
