Self-inspection vs. independent control - what's the difference?

Self-inspection is carried out by you - as contractor or executing party - as work progresses. It follows the control points, control types and control levels set out in the B2 control plan, and forms the basis for the B3 control report.

Self-inspection isn't a formality: it's where most of the actual control happens, because the people doing the work are closest to spotting an error while it's still cheap to fix - often before the next stage of work has even begun.

Independent control is carried out by a person who did not take part in designing or executing the work being checked. In structural classes 2 and 3 this can be a colleague in the same company; in structural class 4 it is supplemented by third-party control. It verifies, by sampling or, for high structural classes, systematically, whether self-inspection is reliable.

The requirement rises with the structural class: from spot-checks at lower classes to full, systematic independent control at the highest. From a certain class upward, it's no longer optional - it's a requirement that must be met before the building can be approved.

The results of self-inspection are documented in the B3 control report, which the independent inspector uses as their starting point when assessing whether self-inspection holds up. When self-inspection works well - with clear, ongoing documentation - independent control typically becomes a simpler, faster process.

The reverse is also true: poorly documented self-inspection makes it hard for the independent inspector to approve anything, because there's nothing solid to verify. The two stages aren't independent of each other in practice, even though they're separate in theory.

The independent inspector must not have taken part in designing or executing the work being checked (BR18 §§ 526 and 526 a). In structural classes 2 and 3 the inspector may be employed by the same company; structural class 4 additionally requires third-party control. Many still choose an independent advisor, another engineering firm, or a specialised control partner, depending on the project's scope and structural class.

For many smaller construction firms, simply finding a qualified independent inspector with the right experience in their type of building - on short notice, once construction is already underway - is a practical challenge in itself.

A frequent misunderstanding is thinking independent control replaces self-inspection. It doesn't - self-inspection still has to be carried out and documented in full, regardless of whether independent control is also required. Another misunderstanding is assuming independent control only concerns the final check at handover. In practice, it often tracks the building throughout, as the structural class's requirements trigger concrete control points along the way.

On a project in structural class KK3, the carpenter carries out self-inspection of a load-bearing timber structure on an ongoing basis and documents it in the B3 report. An independent inspector visits the site periodically, reviews a selection of the documented control points, and compares them against the actual work on site.

If the documentation is clear and complete, the independent inspector can often approve quickly. If it's lacking, the inspector must either request supplementary documentation or carry out further spot-checks - which delays the process for everyone.

The cost depends on the building's structural class, scope, and how often the inspector needs to visit the site. The better self-inspection is documented, the less time the independent inspector typically needs to verify it - which can keep the cost down.

It happens that an independent inspector assesses something differently from the contractor's own self-inspection. In those cases, the independent inspector's assessment generally carries more weight, precisely because the control exists to be an extra, impartial check.

The practice is therefore to review the discrepancy concretely - often together with the designing engineer - to clarify whether self-inspection missed something, or whether it's simply a difference of interpretation that can be resolved without further work.

Beyond the formal qualification requirements, it makes sense to consider the inspector's experience with your specific type of building and structure. An inspector experienced in exactly the structural type you're working with can often complete the control faster and with fewer open questions along the way.

It also helps to clarify early how and how often the inspector expects to visit the site, so it can be built into the construction schedule from the start, rather than becoming a source of delay later.

A well-functioning collaboration is characterised by the independent controller being brought in early enough to plan visits around the project's actual progress, rather than being contacted only once a control point is already about to be covered by the next stage of work. Early involvement lets the controller prioritise visits according to where the consequence of an error would be greatest.

The agreement with the independent controller should clearly state how many visits are included, and what happens if additional visits become necessary because of incomplete self-inspection. Without that clarity, disagreement over extra costs can easily surface midway through construction, at the point it's most disruptive to progress.

Before the independent controller visits, it helps to have the relevant part of the B3 report ready and easy to access, and to make sure the control points that need verifying are still visible and not already covered by the next stage of work. A small amount of preparation here can shorten the visit itself considerably.

Independence attaches to the person and the task: the controller must not have taken part in the work being checked. In structural classes 2 and 3 the controller may be employed by the same company; structural class 4 additionally requires third-party control with no financial or organisational ties to the companies involved (BR18 §§ 526 and 526 a). That's an important distinction if you're considering using the same partner for this role across several projects.

If the independent controller raises a concern early in the process, it pays to treat it as useful information rather than as criticism of the self-inspection carried out so far. Catching an issue early, while the relevant structure is still accessible, is considerably cheaper and less disruptive than catching the same issue once the work has moved on.

The controller's early involvement, in this sense, isn't just a formality - it's one of the more effective ways to avoid costly rework later in the project.

Beyond how many visits are included, it helps to be explicit about who bears the cost if extra visits are triggered by gaps in self-inspection rather than by the project's genuine complexity. Leaving this unstated tends to produce exactly the kind of disagreement it was meant to prevent, right when the project can least afford the distraction.

If the independent controller changes partway through a project, you'll want to arrang a proper handover between the outgoing and incoming controller, covering what's already been checked and what remains open. Without that handover, the new controller may either repeat work unnecessarily or, worse, assume a point was covered when it wasn't.

Before appointing an independent controller, it's a good idea to ask directly about their experience with similar structural classes and building types, rather than assuming any qualified controller will bring equally relevant judgement. A controller familiar with the specific type of construction involved tends to spot the right issues faster than one encountering that structural type for the first time. It also helps to ask how the controller documents their findings, since a clear, well-structured report makes it considerably easier for the structural engineer to follow and approve.