Can the building control officer sign off without engineer calculations?

No — building control officers are not engineers and will not accept verbal assurances or builder's drawings for structural elements. Every steel beam, foundation design, opening-up of load-bearing walls and basement excavation requires stamped engineering calculations. The exception is replacement-like-for-like work where no structural change occurs (replacing identical roof tiles, refacing a wall without affecting structure).

Do I need an engineer for permitted development works?

Planning permission and building regulations are separate regimes. A loft conversion or rear extension may be permitted development for planning but still requires building control approval — which still requires structural calculations for every steel beam, opening and new foundation. PD status does not exempt the works from structural design.

How long do structural calculations take?

A standard loft or extension engagement runs 2–4 weeks from instruction to issue of stamped calculations, assuming an early site visit and timely architect drawings. Basement engagements typically run 4–8 weeks to allow for ground investigation report review, soil bearing capacity testing, and detailed underpinning sequence design. Plan structural engagement into the programme alongside the planning application so building control submission is not delayed.

Structural Engineer Cost London 2026 | Builderr

How Much Does a Structural Engineer Cost in London?

Structural engineer fees in London 2026: £800–£1,800 for a loft conversion, £1,200–£3,500 for a single or double-storey extension, £4,500–£12,000 for a basement excavation including underpinning design, and £2,500–£6,000 for whole-house renovation with opened-up structure. Building control accepts only chartered (CEng) or IStructE corporate member calculations on most London applications.

When you legally need a structural engineer

Under building regulations and Approved Document A, structural calculations are required for: any new beam, lintel or column carrying load (steel goalpost frames, ridge beams, dormer support, opening-up of internal walls); any change of use that increases imposed floor loading (loft converted from storage to habitable); any new foundation including underpinning, mini-piles, piled retaining walls; any basement excavation; any retaining wall above 1.5m; any addition that loads the existing structure beyond its original design (new roof structure, double-storey extension on single-storey foundations). London councils will not approve building regulations applications for any of these without calculations stamped by a chartered structural engineer or a corporate member of the IStructE. Calculations also commonly underpin party wall surveys, underpinning designs and Section 80 dangerous structure responses.

What's included in the typical fee

A typical loft conversion structural engagement at £800–£1,800 includes: a site visit and structural appraisal of existing roof and floor, design of new floor joists and trimmers, steel beam sizing for ridge or purlin replacement, dormer support framing, opening-up details for new staircase, calculations stamped and signed for building control submission, and one revision round to address building control comments. Extension engagements typically add foundation design (strip or raft), lintels, structural openings (goalpost frames for bifold or sliding doors), wall ties and roof structure. Basement engagements add full underpinning design (typically pin-by-pin sequencing schedule), retaining wall design, dewatering and shoring strategy — a major engineering exercise that is one of the highest-cost items on a London basement build. Site inspections during construction (typically 3–6 visits) may be charged separately at £350–£600 per inspection.

How to engage and what to look for

Use only chartered engineers (CEng MIStructE or CEng MICE) or corporate IStructE members for any structural work in London — most councils reject calculations from non-chartered engineers. Verify membership through the IStructE register before engaging. The engineer should hold £2 million professional indemnity insurance minimum (£5 million is typical for basement and underpinning specialists). Engage early — before the architect finalises the design, so structural feasibility informs the planning drawings rather than driving expensive late-stage redesign. For Builderr design-and-build contracts, the structural engineer is engaged directly by us as part of the fixed price, eliminating the separate fee and ensuring calculations align with the build sequence.