Structural calculations and engineering for extensions, conversions and new builds
Structural Engineering and Calculations
Structural calculations are the engineering sign-off needed whenever a project alters or removes a load-bearing element — a steel beam over a knocked-through wall, a new foundation for an extension, or a strengthened floor for a loft conversion — set out in a structural drawing and calculation pack that Building Control checks the work against.
Definition
What Structural Calculations covers
Structural engineering covers the calculations and drawings that prove a proposed structure — a beam, foundation, floor or wall — will safely carry the loads placed on it. For most residential projects this means sizing steel beams (RSJs) for openings, designing foundations for extensions, checking floor strengthening for loft conversions, and producing the structural drawings and calculation pack that Building Control require as part of the Building Regulations approval.
Suitable for
- Extensions, loft conversions and new builds where structural calculations are needed for Building Regulations approval
- Knock-throughs and structural alterations that remove or alter a load-bearing wall
- Clients who already have architectural drawings (their own or from an independent architect) and need the structural calculations to go with them
Not suitable for
- Work with no structural element — cosmetic redecoration, non-structural partition changes, or like-for-like repairs
- Emergency structural failures requiring an urgent site assessment — call us directly rather than starting with an enquiry form for anything that looks unsafe
Process
How the work is carried out
- 01
Site survey
Assessing the existing structure — what it is, what condition it's in, and what the proposed works need it to do.
- 02
Structural design
Sizing the beams, foundations or floor strengthening needed, coordinated with the architectural drawings where we're producing both.
- 03
Calculations pack
Preparing the formal calculation pack and structural drawings in the format Building Control and the wider design team need.
- 04
Building Control liaison
Submitting calculations to Building Control and handling any follow-up queries through to approval.
- 05
Construction support
Available through the build for any site queries as the structural work is carried out.
Typical timescale
Structural calculations for a typical extension or loft conversion usually take one to two weeks once the design is fixed; more complex schemes with multiple structural elements take longer.
Cost guidance
Structural calculation fees depend on the number and complexity of structural elements involved (a single beam versus a full new-build structural design) and are quoted as a fixed fee once we understand the scope.
Limitations and exclusions
- We calculate and design the structure; the architectural design itself is delivered through our architectural design service (or your own architect's drawings, which we're happy to work from)
- Existing structures are assessed from what's visible and from drawings provided — opening up work may reveal conditions that require the design to be revisited
Areas we cover
Structural Calculations across Sussex, Surrey, Kent and South London
Local property styles, planning authorities and neighbourhood coverage for structural calculations in each town we work in.
Related services
You may also need
FAQs
Structural Calculations FAQs
Do I need structural calculations for a loft conversion?
Almost always — the existing floor typically needs strengthening to take habitable-room loading, and any new stair opening or dormer usually needs its own structural design. Building Control will check the work against a calculation pack as part of sign-off.
Can you provide calculations for a beam I've already had designed elsewhere?
We generally produce calculations as part of a coherent structural design for the whole project, but get in touch with what you have and we'll advise whether we can work from it or whether it needs revisiting.
Do you work with independent architects, or only your own designs?
Both. We regularly provide structural calculations for drawings produced by independent architects and designers, not just our own architectural design service.
How do structural calculations fit with Building Regulations approval?
The calculation pack is submitted to Building Control (or your approved inspector) alongside the Building Regulations drawings, and forms part of what's checked at each inspection stage through to the completion certificate.
Discuss your structural calculations project
Tell us about the property and what you have in mind, and we'll arrange a site visit.
Last reviewed 2026-07-19.