What are higher-risk buildings? The 18-metre rule explained

If you own, manage, or are responsible for a residential building in England, one of the most important questions you now face is straightforward but consequential: does your building qualify as a higher-risk building?

The answer determines whether you are subject to the most stringent tier of regulation under the Building Safety Act 2022. This regime introduces requirements for mandatory registration, named Accountable Persons, Golden Thread obligations, and direct oversight from the Building Safety Regulator. Getting this wrong in either direction carries real consequences: failing to register an in-scope building is a criminal offence, while incorrectly assuming you are in scope can lead to unnecessary compliance burden.

This article explains exactly what makes a building higher-risk, how to measure your building correctly, what is excluded, and what your obligations are once you know your status.

Why the higher-risk building category was created

The Building Safety Act 2022 was the UK government’s legislative response to the Grenfell Tower fire of June 2017, in which 72 people lost their lives. The fire exposed serious failings in how high-rise residential buildings were designed, constructed, and managed. In particular, it highlighted how accountability for building safety had become fragmented and unclear.

The Act introduced a new, more stringent regulatory regime specifically for buildings deemed to carry the greatest risk. These include buildings where evacuation is significantly more complex, and where the consequences of fire or structural failure are most severe. These buildings are classified as higher-risk buildings (HRBs), and they are now subject to continuous oversight by the Building Safety Regulator (BSR), an independent body that sits within the Health and Safety Executive.

The legal definition: what makes a building higher-risk?

Under Section 65 of the Building Safety Act 2022, a higher-risk building during the occupation phase is defined as a building in England that meets all three of the following criteria:

• It is at least 18 metres in height, or has at least 7 storeys
• It contains at least 2 residential units
• It is not an excluded building type (see below)

Crucially, the height and storey thresholds work as alternatives, your building only needs to meet one. A 7-storey building that is 16 metres tall still qualifies as a higher-risk building. A 20-metre building with only 6 storeys also qualifies. You do not need to meet both thresholds.

The government estimates that approximately 13,000 existing buildings in England meet this definition.

Which buildings are excluded?

Even if a building meets the height or storey threshold, certain building types are excluded from the in-occupation regime under the Regulations:

• Secure residential institutions (such as prisons or detention centres) when the entire building is used for that purpose
• Hotels when the entire building is used as a hotel
• Military barracks and living accommodation provided by the Ministry of Defence for armed forces personnel
• Accommodation for visiting forces or designated international headquarters and defence organisations

It is important to note that these exclusions apply only to the in-occupation regime (Part 4 of the Act). Under the design and construction regime (Part 3), hospitals and care homes are included if they meet the height threshold, even though they are excluded from Part 4.

What counts as a residential unit?

The building must contain at least 2 residential units to be in scope. Under the Act, a residential unit is defined broadly as any dwelling or unit of living accommodation. This includes:

• Flats and apartments
• Studio flats
• Houses in multiple occupation (HMOs)
• Individual bedrooms within shared university halls of residence
• Units within supported accommodation buildings

What happens once your building is classified as higher-risk?

Classification as a higher-risk building triggers a substantial set of legal obligations. These are not optional or advisory, they are duties backed by criminal enforcement.

• Registration: Higher-risk buildings must be registered with the Building Safety Regulator. Failure to register without reasonable excuse is a criminal offence that can result in prosecution and, in serious cases, imprisonment.
• Accountable Person duties: Every higher-risk building must have at least one Accountable Person. This is the party responsible for fire and structural safety risks in the building. 
• The Golden Thread of information: Accountable Persons must maintain accurate, up-to-date digital records about the building. Including its design, construction history, current condition, and safety management. This is known as the Golden Thread. The information must be structured, accessible, and defensible to the Building Safety Regulator.
• Safety case report: Accountable Persons must prepare a safety case report demonstrating that they have identified and are actively managing all fire spread and structural collapse risks in the building. This must be kept current and must be available for inspection.
• Resident engagement: Accountable Persons have statutory obligations around communicating with residents. This includes providing safety information, and establishing a residents’ engagement structure for the building.
• Inspection readiness: The Building Safety Regulator has significant enforcement powers, including the ability to carry out assessments of whether a building’s Accountable Persons are meeting their duties. Being unable to demonstrate compliance, through clear records, documented risk management, and traceable evidence, is not simply an administrative failure. It is a regulatory risk.

Summary

A higher-risk building in England is one that meets the height or storey threshold (18 metres or 7 storeys), contains at least 2 residential units, and is not an excluded type. Correct measurement, from the lowest adjacent ground level to the top occupied floor surface, is critical and frequently misunderstood. Once a building is classified as higher-risk, obligations around registration, Accountable Person duties, the Golden Thread, and Safety Case reporting apply in full.

If you are responsible for a building that may fall within scope, the first step is establishing with confidence whether it does, and if it does, ensuring your compliance structure is fit for purpose.

Complitas is a building safety compliance platform designed to help organisations responsible for higher-risk buildings stay audit-ready, maintain their Golden Thread, and meet their Accountable Person duties with clear accountability and defensible evidence. Explore the benefits and uses of implementing Building Compliance Solutions for Higher-Risk buildings.