Building Control Approval for Structural Engineering: A Complete Guide

Most homeowners don’t give much thought to Building Control until a project is already underway and someone mentions it. At that point it feels like a bureaucratic hurdle — forms to fill in, inspections to schedule, a process that exists to slow things down.

In practice, Building Control is the system that makes sure your building is safe after the professionals leave. The structural calculations your engineer produces aren’t just a document for a file — they’re the technical basis on which Building Control accepts or queries the structural design of your project. Understanding how the process works removes uncertainty and prevents expensive mid-project surprises.

What Building Control actually is

Building Control is the regulatory system established under the Building Regulations Act 1984, administered through Building Regulations 2010 (and the significant amendments brought in by the Building Safety Act 2022). Its purpose is to verify that new construction work meets the minimum standards required for safety, health, energy efficiency, and accessibility.

For structural work, the relevant requirements are in Part A — Structure. Part A requires that:

– The building’s structural elements must safely carry their design loads
– Ground settlement must not impair the stability of any part of the building
– Wind and other horizontal forces must be resisted without excessive deformation
– The building must not suffer disproportionate collapse if a part of the structure is damaged

Structural calculations from an engineer are the primary means of demonstrating compliance with Part A. The BCO doesn’t independently verify the engineering — they check that engineering calculations exist, that they’re from a qualified professional, and that the work on site matches what was designed.

What a Building Control Officer can check on site

The BCO’s role is compliance, not design. There’s a clear boundary between what they can assess visually on site and what requires engineer input to resolve.

What the BCO can check:

– Ground conditions at foundation level — visual inspection of the soil at the bottom of the excavation. They’re checking that it looks suitable (firm clay, sound gravel, no soft patches) and that the depth reaches the specification on the structural drawing.
– Foundation dimensions — width and depth of excavation before concrete is poured.
– Condition and dimensions of masonry at beam bearing points — that the wall is thick enough (generally ≥100mm), properly bonded, and in acceptable condition.
– Installation of padstones — that they’re present, correctly sized, and properly bedded.
– Beam installation — visual check that the correct designation of beam appears to be installed at the right level with adequate bearing length.
– Structural timber — visual check that joist sizes, spacings, and notching locations are consistent with the drawings.

What the BCO cannot check:

– Whether the beam is the right size for the loads (that’s an engineering calculation, not a visual check)
– Whether the foundation design is adequate for the actual loads (that’s what calculations are for)
– Whether the connection details are correct in any engineered sense (they can see the connections but cannot verify the bolt patterns, weld specifications, or bearing stresses)

If the BCO sees something that looks inconsistent with the drawings, or if conditions on site differ from what the engineer assumed, they pause work and request the engineer review the situation. That review is structural engineering work — not BCO work.

The inspection stages for a typical extension or wall removal

Before you start: You notify Building Control either via a Full Plans application (you submit drawings and calculations upfront, they’re approved before work starts) or a Building Notice (work proceeds without pre-approval, at the owner’s risk, with inspections carried out as work progresses). Full Plans gives you more protection — you know the design is approved before groundbreaking.

Excavation: BCO inspects the foundation trench before concrete is poured. They confirm depth, width, and ground condition at formation level. Concrete should never be poured before this inspection. If it is, the BCO can require the foundation to be exposed for inspection.

Steelwork: For projects involving structural steel, the BCO typically requests a notification when steelwork is installed and before it’s concealed (plastered over, cased in). They check beam levels, bearing, and padstone installation.

Drainage: For extensions over or near existing drains, the BCO checks the drainage bridge or clearance detail.

Completion: Final inspection before the completion certificate is issued. The certificate is the formal record that the work was built in accordance with the Regulations. You’ll need it for conveyancing.

The Principal Designer role: what it means for your project

Since 2023, the Building Safety Act amendments to the Building Regulations introduced a mandatory dutyholder framework. For most residential projects this means:

Domestic client: The homeowner commissioning the work. In law, certain duties rest with the client — ensuring a Principal Designer and Principal Contractor are appointed where required.

Principal Designer (PD): The person or organisation responsible for planning, managing, and monitoring the design phase so that all designs work together and comply with Regulations and health and safety law. The PD must have the skills, knowledge, experience, and organisational capability to coordinate every design discipline.

Principal Contractor (PC): The contractor responsible for planning, managing, and monitoring the construction phase. Typically the main builder.

For projects with more than one contractor working simultaneously, a PD must be appointed. The PD is required to sign a compliance statement before Building Control can accept the application or issue a completion certificate.

Who should be the PD?

| Scenario | Who signs as PD |
|—|—|
| Architect leading the design | The architect — they control and coordinate all design disciplines |
| Design and build contract | The design-and-build contractor |
| No architect, homeowner hires builder | The builder (who becomes both PD and PC) |
| Homeowner designs project themselves | The homeowner, if competent to do so |

PorthouseDean provides structural calculations — we do not act as Principal Designer unless specifically appointed and contracted to do so. Our scope is structural design. The PD coordinates all design disciplines (structural, architectural, fire, acoustic, thermal) — that requires a separate appointment, a wider scope, and additional fee and PI cover.

If your BCO asks PorthouseDean to sign the PD declaration, contact us and we’ll explain the position. The declaration should come from whoever is coordinating the wider design — almost always the architect or main contractor.

What “remote structural design” means and why it works

PorthouseDean designs virtually, without mandatory site visits. This surprises some clients and their builders, who expect an engineer to walk the site and measure everything before producing calculations. Here’s why it works:

Conservative assumptions: Where exact measurements or hidden conditions can’t be confirmed remotely, engineers use conservative worst-case assumptions. The design is made to work under the most demanding plausible conditions, not just the most likely ones.

Client-supplied information: Before calculations begin, the engineer collects: photographs of the existing structure, floor plans, section views, any existing drawings available, and confirmation of key measurements. A virtual site visit guides the client through exactly what to capture on video or photograph.

Verification instructions in the drawings: The structural drawings include instructions for verifying key conditions on site before work proceeds. If the actual conditions differ from what was assumed, the contractor reports back to the engineer for review.

One free revision: If conditions found on site require a design change, the first revision is included. This isn’t a loophole — it’s how remote design has worked for thousands of projects successfully.

Across our project history, well over 9,000 projects have been completed to Building Control standard using this approach. The BCO inspects site conditions; the calculations cover the design. Both roles work.

What happens when Building Control raises a query

BCO queries during construction are normal. They’re not a sign that the calculations are wrong — they’re the BCO doing their job, cross-referencing what they see on site with the approved design.

Common triggers for queries:

– Ground conditions at foundation level look different from the assumption in the design (more fill, softer clay, an unexpected drain)
– A beam level or bearing detail doesn’t look consistent with the drawing
– The contractor has made a site change without notifying the engineer
– A non-standard detail isn’t covered explicitly by the existing calculations

At PorthouseDean, a BCO query goes directly to your dedicated engineer. They review the issue, respond to the BCO directly, and if a design amendment is needed, issue revised drawings — the first revision is included in the original fee. You don’t need to manage this process or understand the technical content; your engineer handles it.

What to keep after completion

After Building Control issues the Completion Certificate, retain the following:

1. The Completion Certificate itself — proof that the work was inspected and approved. This is required for conveyancing.
2. The approved structural drawings — record of what was designed and installed.
3. The structural calculations — technical backup for the design.
4. The Building Control application reference — for any future queries from a solicitor or purchaser.

If these documents are lost, the Local Authority may hold digital records of the Building Control application. The structural engineer may also hold copies of the calculations and drawings.

Approved Inspectors vs Local Authority Building Control

Building Control is carried out either by the Local Authority (LABC) or by a private Approved Inspector (AI). The system is broadly equivalent — both use the same Regulations, both carry out the same inspection stages. The differences are administrative and commercial.

Since the Building Safety Act 2022, Approved Inspectors have been replaced with Registered Building Control Approvers (RBCAs) — private bodies that have been registered with the Building Safety Regulator. In practice, the market continues with similar providers under new terminology.

Either route is acceptable. Your choice may be influenced by which BCO your builder has a working relationship with, or by the local authority’s turnaround time for plan approvals.

Summary: the engineer’s role vs the BCO’s role

| Question | Answered by |
|—|—|
| Is this beam strong enough? | Structural engineer (calculations) |
| Is this beam installed correctly? | BCO (site inspection) |
| Is the foundation depth appropriate for this ground? | Structural engineer (design) with BCO confirmation (site inspection) |
| Is this construction consistent with the approved drawings? | BCO (site inspection) |
| Has Building Control approved the project? | BCO (Completion Certificate) |

The two roles are complementary. The engineer produces a design that complies with Regulations; the BCO verifies it’s been built as designed. Getting the engineering right from the start is the most effective way to sail through Building Control without delays.