How Structural Engineers Work With Your Builder
Structural Engineering Isn't Just for Complex Projects
Many homeowners assume a structural engineer is only needed for unusual or ambitious projects — something large, something deep, something complicated. In reality, most standard residential projects in London require structural engineering input.
A loft conversion almost always needs a structural engineer. The new floor needs designing. The existing ceiling joists may not be adequate. There will be a structural beam — an RSJ or similar — spanning over the new staircase opening. The engineer calculates what's needed and produces drawings that Building Control and your contractor can work from.
An extension typically needs a structural engineer too. Foundations need to be specified. The new opening from the existing house into the extension needs a beam calculation. If there's a flat roof, it needs to be designed. If you're removing a chimney breast, that's a structural alteration requiring engineering sign-off.
Getting the structural engineer right, and getting them involved at the right time, is one of the factors that most separates smooth projects from difficult ones.
When Should You Appoint a Structural Engineer?
The best time to appoint a structural engineer is before or during the planning stage — ideally as soon as the design concept is clear enough for them to assess feasibility.
Leaving structural engineering to the last minute — appointing after planning permission is granted, or worse, after the build has started — is a common source of delay, cost surprises, and abortive work. If the engineer specifies a beam size or foundation depth that differs from what was assumed during the tender, everything shifts.
If your architect is involved, they will often suggest or appoint the structural engineer. In a design-and-build model, the contractor may commission the engineer directly. Either approach can work — what matters is that the engineer is involved early, their information is complete before work starts, and any changes during construction are managed formally.
What Does a Structural Engineer Produce?
The structural engineer's output is typically a set of drawings and calculations. These include:
Structural calculations — the detailed numbers behind every beam, joist, foundation, and connection. These go to Building Control as part of the full plans application (or are available for inspection under a Building Notice route).
Structural drawings — plan and section drawings showing beam positions, floor joist layouts, connection details, and foundation specifications. These are what the contractor works from on site.
Connection details — how beams bear onto walls, how joist hangers are specified, how new and existing structure connect. These look like small details on paper but matter enormously in practice.
How Does the Structural Engineer Work With the Contractor?
In a well-run project, the structural engineer and the contractor are in regular contact — particularly during pre-construction and at key stages during the build.
Before work starts, the contractor should review the structural drawings carefully and raise any practical questions or clashes with the existing building. A beam calculated on the drawings might need to sit in a position that creates a conflict with a flue, a hidden beam, or an existing structural element. These conflicts are far better surfaced before the wall is opened up than after.
On site, as works progress, the contractor calls for Building Control inspections at the structural stages — beam installation, foundation depth, joist layout. If the engineer has specified a requirement for inspection by their own practice, that needs to be coordinated too.
If conditions differ from what was expected — hidden steels, an older foundation in poor condition, a chimney breast in a different position — the contractor should refer back to the structural engineer before proceeding. This is standard professional practice, and it protects everyone.
What Happens Without Proper Structural Engineering?
Structural failures on residential projects are rare but not unknown. More commonly, the consequences of inadequate engineering are subtler: beams that deflect too much over time, floor structures that feel bouncy, cracks appearing at new openings, or damp penetration through inadequately specified flat roofs.
More immediately, Building Control will not sign off a project without structural calculations where they are required. And without a Building Regulations completion certificate, you may face problems when you come to sell your home. Retrospective sign-off is possible but costly and uncertain.
Who Commissions the Structural Engineer?
This is sometimes a source of confusion. The structural engineer can be commissioned by:
- The architect, as part of their design team, with costs passed to the client
- The homeowner directly, on the advice of the architect or contractor
- The design-and-build contractor, who coordinates the full design package
In all cases, the homeowner is ultimately paying for the structural engineer's work and should understand what documents are being produced and when.
Talk to RCB Design & Build
At RCB Design & Build | A2Z Principal Contractors, structural engineer coordination is part of how we work — not an afterthought. We manage the relationship between design, engineering, Building Control, and delivery so that structural information is ready before work starts and properly implemented on site. If your project involves structural works and you want a contractor who treats engineering coordination seriously, get in touch.
Call: +44 7359 872594 Email: contact@rcbgroup.co.uk Web: www.rcbgroup.co.uk