Structural Engineer Guide London 2025
When you need a structural engineer, what they do, typical costs, and how to find the right one for your extension project.
Quick Answer
Most London extensions need a structural engineer for foundation design, steel beams, and building control approval. Typical cost: £500-£2,000 depending on project complexity.
£500-£2,000
Typical cost
1-2 weeks
Turnaround
CEng/MIStructE
Key qualification
Check your specific property constraints
Free Property CheckKey Facts
- Typical cost: £500-£2,000 for extension calculations
- When needed: Steel beams, wall removal, foundations, loft conversions
- Turnaround: 1-2 weeks typically for calculations
- Qualification: Look for CEng, MIStructE, or MICE
A structural engineer ensures your extension is safe and stable. They design the structural elements—foundations, beams, lintels—and provide calculations that building control requires before approving your project. Most extensions need structural input at some point.
When You Need a Structural Engineer
Removing Load-Bearing Walls
Creating open plan spaces by removing walls. Engineer designs steel beams and specifies temporary support needed during work.
New Extensions
Foundation design, wall construction, roof structure, and any connections to the existing building.
Loft Conversions
Floor strengthening, dormer construction, staircase opening. Most loft conversions need structural calculations.
Basement Excavations
Complex structural work including underpinning, waterproofing design, and temporary works during construction.
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Structural Engineer Costs
| Service | Typical Cost |
|---|---|
| Single beam calculation | £300 - £500 |
| Small extension (rear) | £500 - £1,000 |
| Loft conversion | £600 - £1,200 |
| Two-storey extension | £800 - £1,500 |
| Basement conversion | £2,000 - £5,000+ |
| Site visits | £150 - £300 each |
What You Get
Structural Calculations
Mathematical calculations proving the structure is safe. Building control requires these before approving work.
Structural Drawings
Detailed drawings showing beam sizes, foundation depths, steel specifications, and connection details.
Specification Notes
Written instructions for builders covering materials, workmanship standards, and construction sequence.
Site Inspections
Visits during construction to check work matches design. Often required for steelwork and foundations.
Planning an extension? Get a full cost breakdown including structural engineer fees.
Try our free calculator →Finding a Structural Engineer
- Institution of Structural Engineers: Search istructe.org for chartered engineers
- Institution of Civil Engineers: ice.org.uk member search
- Architect recommendations: Your architect will have engineers they work with regularly
- Builder recommendations: Experienced builders know reliable local engineers
Free AI Assistant
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Frequently Asked Questions
Do I need a structural engineer for a small extension?
Usually yes, at least for foundation design and any connections to the existing house. Even small extensions may need steel beams. Building control will require structural calculations before approving the work.
Can my architect do structural work?
No, unless they're also qualified as a structural engineer. Architects design spaces and layouts; structural engineers ensure buildings are safe and won't fall down. These are separate professional qualifications.
What's the difference between structural engineer and surveyor?
Surveyors assess existing buildings through condition surveys and valuations. Structural engineers design new structures and alterations, providing calculations and specifications for construction work.
How long do structural calculations take?
Typically 1-2 weeks for standard extension calculations. More complex projects like basements may take 3-4 weeks. Rush services are available for an additional fee.
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Or email hello@mayfairstudio.co.uk · 07405 920944