Control type, control level and control scope in a DS1140 control plan

Control type describes the method - for example visual inspection, physical measurement, or calculation control of a given point. The choice depends on what can actually reveal an error at that specific place in the structure: a visual check can reveal a visible crack, but not incorrect sizing, which instead requires a calculation check.

It's therefore not enough to simply write "checked" next to a point - the control type has to match what actually needs to be verified.

Control level sets how thorough the check needs to be, based on the building's structural class. A critical load-bearing element in a high structural class requires a higher control level than a less critical element in a low class.

In practice, this means the same type of control point - a connection between two load-bearing elements, for example - can require different levels of documentation, depending on where in the structure it sits and how large the consequence of an error would be.

Control scope specifies whether 100 percent of an element is checked or only a sample, and how frequently. This is often where a control plan gets rejected - because the scope doesn't match the structural class, for example by assuming spot-checks where the class requires systematic, full control.

Scope is closely tied to control level: a high control level without a matching control scope doesn't actually deliver the assurance the structural class requires.

Picture a reinforced concrete column in a building with a high structural class. The control type could be a combination of visual inspection of reinforcement placement before pouring, and a calculation check of the column's sizing. The control level would be high, because a failure here has serious consequences. The control scope would typically require that every column of this type be checked - not just a sample - precisely because the consequence of failure is significant.

Because they describe related, but distinct, questions about the same control point: how, how thoroughly, and how much. In everyday conversation they often get collapsed into a single question - "is it checked enough?" - but a B2 plan that doesn't separate them clearly gives the person carrying out the work nothing concrete to act on.

For a welded connection in a load-bearing steel structure, the control type could be a combination of visual inspection and non-destructive testing of the weld. The control level would depend on how critical the connection is to the overall stability of the structure. The control scope could be all critical connections, while less critical connections are checked by sampling.

This differentiation - not everything checked equally thoroughly - is exactly the point of separating control type, level and scope: resources go where the consequence of failure is greatest.

The B2 plan should briefly justify why a given control level and scope were chosen for the most critical points - not just state the figures. That makes it easier for the structural engineer to follow the reasoning and reduces the risk of the plan being sent back with questions about the justification.

A high control level combined with a large control scope means more time spent on control and documentation - and therefore a higher cost. That isn't something you can cut back to save money if the structural class requires it, but it makes sense to know when the building's budget and schedule are set.

Conversely, a precise, well-justified plan that doesn't over-specify the control scope beyond what the structural class actually requires can keep costs down without compromising safety.

If the project changes along the way - for example through an addition to the structure - control type, control level and control scope for the affected points should be revisited, not simply assumed unchanged. It's part of the same process that applies if the structural class as a whole changes.

Revisiting these three systematically whenever the project changes significantly is a simple habit that reduces the risk of an otherwise solid control plan gradually losing its precision as construction proceeds.

If control type, level and scope are reused from an earlier, similar project, each point still needs to be reviewed specifically against the new building's structural class and complexity - an assumption that was correct on one project isn't automatically correct on the next, even for apparently similar structures.

Because the scope of control directly affects the overall schedule, and therefore the cost, it's a good idea to have control type, level and scope settled before final quotes are obtained from contractors, rather than afterwards. A late change to the control scope can otherwise trigger a follow-up negotiation on price that could have been avoided.

It isn't enough for control type, level and scope to be correctly set in the plan - they also need to be communicated clearly to the people who actually carry out the control on site, ideally in a short kick-off at each new phase of construction. Without that communication, an otherwise well-written plan risks never being followed correctly in practice.

On a renovation of an existing structure, control scope can be harder to fix than on a new build, because part of the structure is already hidden or only partly accessible for inspection. Here it's often necessary to supplement the planned control with an assessment of what can be adequately documented from existing drawings and materials, versus what genuinely requires physical access.

If it becomes clear during construction that the originally set choices for control type, level and scope don't match the actual complexity showing up on site, it's better to formally revise the choices with the structural engineer than to quietly deviate from the plan on site without updating the paperwork. A formal revision ensures the B2 plan always reflects the control that's actually being carried out.

If several advisors are involved in the same project - for example one for concrete and one for steel - it pays to clarify early how their respective assessments of control type, level and scope are combined into one consistent B2 plan. Without that coordination, there's a risk of conflicting requirements for control scope on structures that are, in reality, connected.

Even a carefully set control type, level and scope can turn out to be a poor fit once construction reveals the actual condition of the site - unexpected ground conditions, for instance, or a design change partway through. Treating the original scope as fixed no matter what emerges on site tends to produce documentation that technically exists but doesn't reflect what was really checked.

Some insurers set out minimum expectations for how thoroughly control is documented on a given project, separate from what DS1140 itself requires. It helps to check these against the control type, level and scope already set in the plan, so the two don't end up in conflict once a claim is actually assessed.