Structural Engineer Cost for Extensions 2026
A structural engineer calculates the steel beams, foundations, and load paths that keep your extension standing. Every extension that removes or alters a load-bearing wall needs structural calculations — it is not optional.
Cost breakdown
What structural engineers charge
Structural calculation fees vary by complexity: simple beam calculation (one opening): £300–£500. Extension structural package (beams, foundations, lintels): £500–£1,000. Complex project (two-storey, underpinning, basement): £1,000–£2,500. PlanBuildCo charges a fixed £350 for extension structural calculations.
What is included
A structural package typically includes: beam sizing and specification, padstone details, foundation design (depth, width, reinforcement), lintel calculations for new openings, and a structural engineer's certificate. This is what building control needs to see before approving the structural work.
| Service | Typical Cost |
|---|---|
| Single beam calculation | £300–£500 |
| Extension structural package | £500–£1,000 |
| Loft conversion structural package | £500–£1,200 |
| Two-storey extension | £800–£1,500 |
| Basement/underpinning | £1,500–£3,000 |
| PlanBuildCo (fixed price) | £350 |
Prices based on Dorset rates, 2026
Frequently asked questions
Ready to get started?
Get a fixed-price plan for your project. No obligation, no follow-up calls.
Every plan drawn by qualified drafters in Poole, Dorset
Serving homeowners across Poole, Bournemouth, Christchurch, Wimborne, Wareham, and the wider Dorset area.