Mandatory Occurrence Reporting: What Triggers a Report and How to Stay Compliant

Mandatory Occurrence Reporting is one of the most misunderstood obligations under the Building Safety Act 2022 regime. Construction teams that have operated successfully under CDM and conventional building control for years often approach MOR as though it were similar to accident reporting or non-conformance records. It is not. MOR is a statutory notification obligation to the Building Safety Regulator, with specific triggers, specific timeframes and specific consequences for non-compliance.

This guide sets out what MOR is, what triggers a report, who must report, how to report, and how to build MOR into your site management processes from the outset.

What Is MOR and What Is Its Legal Basis?

Mandatory Occurrence Reporting is the obligation, under Regulation 38A of the Building Regulations 2010 (as inserted by the Building (Higher-Risk Buildings Procedures) (England) Regulations 2023), to notify the BSR when a "reportable occurrence" takes place on or in relation to a higher-risk building during the construction phase.

The obligation flows from the Building Safety Act 2022 and sits alongside the change control plan as a mechanism for ensuring that the BSR maintains oversight of what is happening on site after Gateway 2 approval has been granted. It is not a voluntary safety management tool — it is a compulsory statutory notification regime.

The MOR obligation applies from the point at which Gateway 2 approval is granted until a Completion Certificate is issued at Gateway 3. Any work on the building that falls within the scope of the Building Regulations — which, for an HRB, means essentially all construction activities — is within the scope of MOR.

Who Is Required to Report?

The reporting obligation falls on the Principal Contractor as the primary duty holder during the construction phase. However, the obligation extends to all duty holders who become aware of a reportable occurrence. In practice, this means:

• The Principal Contractor has the primary reporting obligation and must have a documented process for identifying and reporting occurrences
• Designers — including the Principal Designer (Building Regulations) — who become aware of a reportable occurrence in the course of their involvement in the project must notify the Principal Contractor, who must then report to the BSR
• Specialist subcontractors and package contractors are required to bring occurrences to the attention of the Principal Contractor immediately
• The Principal Contractor cannot delegate the reporting obligation to a subcontractor — the report to the BSR must come from the Principal Contractor

What Constitutes a Reportable Occurrence?

This is where most confusion arises. A reportable occurrence is defined under the HRB Procedures Regulations as an occurrence in relation to a higher-risk building during its construction that:

• Involves a failure or potential failure of a safety-critical element of the building — for example, a structural element, compartment wall, fire door assembly, or fire suppression system
• Represents a significant deviation from the approved design that could affect the building's compliance with the Building Regulations, even where the change may not formally trigger the change control plan
• Constitutes a near miss that could, if not addressed, result in the building as constructed not complying with its approved design in a safety-relevant respect
• Involves discovery of information that could reasonably have affected the Gateway 2 application if it had been known at the time of submission — for example, ground investigation findings that alter the structural design basis

The obligation is deliberately broad. The BSR's guidance makes clear that, in cases of doubt, the duty holder should report. The regulator has stated that it will not penalise over-reporting — but will take action against duty holders who fail to report occurrences that objectively should have been notified.

Examples of events that should trigger a MOR assessment include: discovery of a structural defect in a load-bearing element; installation of a fire door that does not match the approved specification; a cavity barrier found to be incorrectly installed over a significant area; a drainage or waterproofing failure that affects a fire-rated floor; or a cladding specification change during procurement that departs from the approved fire strategy.

Reporting Timeframes and Format

Once a reportable occurrence has been identified, the Principal Contractor must notify the BSR within 10 working days. The notification must include:

1. A description of the occurrence and how it was identified
2. The location and extent of the occurrence within the building
3. An assessment of whether and how the occurrence affects compliance with the Building Regulations or the approved Gateway 2 design
4. The proposed remedial action and timescale
5. Confirmation of whether any work has been paused pending the BSR's response

The report is submitted through the BSR's online portal. It should be clear, factual and contain sufficient information for the BSR's case officers to assess the significance of the occurrence without needing to request further information.

Relationship with the Change Control Plan

MOR and the change control plan (CCP) are related but distinct obligations. A change to the approved design that is managed through the CCP process may or may not also be a reportable occurrence. The test for MOR is whether there is a safety-critical concern. The test for change control is whether the change departs from the approved design in a way that requires BSR consent before the change is implemented.

Where an occurrence involves both a reportable event and a notifiable change, both obligations must be discharged in parallel. The MOR report and the change control submission should cross-reference each other. Submitting one without the other where both are triggered is a compliance failure.

Consequences of Non-Reporting

Building MOR into Your Site Management Processes

The most effective MOR regimes are those that are embedded into existing quality management and non-conformance reporting processes — not operated as a separate system. Effective practice includes:

• A project-specific MOR plan submitted at Gateway 2. The plan should identify the specific elements of the project that are most likely to generate reportable occurrences — fire compartmentation, structural connections, cladding assemblies — and describe the site-level process for identifying and escalating potential occurrences.
• Training for site managers and package contractors. Everyone on site should understand the basic MOR trigger criteria. Subcontract packages for safety-critical trades should include explicit MOR obligations.
• A named compliance lead with authority to submit reports. Ambiguity about who is responsible for submitting MOR reports is a common failure point. The MOR plan should name an individual — not just a role — with explicit authority and responsibility.
• Regular compliance reviews during construction. Scheduled compliance reviews — at least monthly on complex projects — at which the non-conformance log is reviewed against MOR trigger criteria, reduce the risk of an occurrence going unreported because it was not recognised as reportable.
• Integration with Golden Thread records. MOR reports and their outcomes should be recorded in the Golden Thread. The Gateway 3 submission will need to demonstrate that all reportable occurrences were identified, reported and resolved.

Applicable Legislation and Guidance

MOR is not optional and it is not administrative. It is a fundamental component of the building safety regime — the mechanism by which the BSR maintains real-time oversight of construction on higher-risk buildings. Getting MOR right from day one of construction is not only a legal obligation; it is the foundation of a credible Gateway 3 application.