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.
Key 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.
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.
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
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.
Can my architect do structural work?
No, unless they're also qualified as a structural engineer. Architects design spaces; structural engineers ensure they don't fall down.
What's the difference between structural engineer and surveyor?
Surveyors assess existing buildings (condition surveys). Structural engineers design new structures and alterations.