What counts as a higher-risk building? The 18m / 7-storey test
A higher-risk building is a building in England that is at least 18 metres tall, or has at least 7 storeys, and contains at least two residential units. Care homes and hospitals that meet the height test are higher-risk at the design and construction stage. Hotels, secure residential and military accommodation are excluded.
What is a higher-risk building under the Building Safety Act?
A higher-risk building is defined by the Higher-Risk Buildings (Descriptions and Supplementary Provisions) Regulations 2023, and the test is simpler than the industry sometimes makes it sound. A building is higher-risk, for the design and construction regime, if it is at least 18 metres tall or has at least 7 storeys, and it contains at least two residential units. Care homes and hospitals that meet the same height or storey test are also higher-risk at that stage.
The word that trips people up is "or". The height and storey tests are alternatives, not a pair you have to satisfy together. A building with seven storeys that comes in under 18 metres is still higher-risk. So is a building over 18 metres with six tall storeys. Whichever threshold you hit first puts you in scope.
What does the height and storey test actually measure?
Height is measured from ground level to the finished floor level of the top occupied storey. Storeys that exist only to house plant or machinery do not count towards either the height measurement or the storey count. That matters on schemes where a rooftop plant enclosure would otherwise tip a building over a threshold it does not functionally cross.
| Trigger | Threshold | Notes |
|---|---|---|
| Height | 18 metres or more | Measured to the finished floor level of the top storey; plant-only storeys ignored |
| Storeys | 7 or more | Plant-only storeys ignored |
| Residential units | At least 2 | Required for the design and construction regime, alongside height or storeys |
If you are close to a threshold, resolve the measurement early and in writing. Being a metre either side of 18 changes which regulator you answer to, how long your programme needs to be, and whether construction can start at all without a Gateway 2 approval.
Which buildings are in scope, and which are excluded?
The residential-unit rule is what keeps the regime focused on where people sleep. A building needs at least two residential units to be caught during design and construction. Care homes and hospitals are brought in expressly, because of the vulnerability of the people inside them, even though their occupants are not in conventional flats.
Several building types are deliberately excluded from the higher-risk definition, however tall they are:
- Hotels
- Secure residential accommodation, such as prisons and young offender institutions
- Military premises and living accommodation
A purely commercial building, an office tower or a shopping centre, is not a higher-risk building for this regime no matter its height, because it has no residential units. That does not mean it escapes fire safety law; it means it is regulated through ordinary building control and the Fire Safety Order rather than the gateways.
Why do some developers design below the threshold?
Because the regime is expensive in time. Faced with 20 or more extra weeks of regulatory programme and a design that has to be fully resolved before a spade goes in the ground, some developers have chosen to redesign schemes to sit below 18 metres and under seven storeys, taking them out of the higher-risk regime entirely.
It is worth being honest that this happens, and worth being clear-eyed about it. Designing below the threshold is lawful. It is also, in some cases, a decision to build a lower, wider, less efficient building purely to avoid a regulator, which is not the same thing as building a safer one. The second staircase mandate, which lands for new residential buildings over 18 metres on 30 September 2026, has sharpened this calculation further, because it raises the cost of staying above the line. Expect the "just under 18 metres" massing to remain common while the regime settles.
What is the higher-risk buildings register?
Occupation brings a separate duty. Every existing occupied higher-risk building in England had to be registered with the Building Safety Regulator by 30 September 2023, and it is the Principal Accountable Person who registers it. For a new building, registration is a step that has to happen before anyone can lawfully occupy it, and it sits alongside, not instead of, the Gateway 3 completion certificate. It is a criminal offence to occupy a higher-risk building before both the completion certificate is issued and the building is registered.
If your building is caught by the definition above, work back from occupation: the register and the certificate are the last two locks on the door, and both take time you need to have in the programme.
Where the definition bites on a real project
The practical value of getting this right early is that the definition decides your whole compliance route. If your building is higher-risk, you answer to the BSR, you need Gateway 2 approval before construction, you run formal change control through the build, and you need a Gateway 3 completion certificate and registration before occupation. If it is not, you are in ordinary building control. The gap between those two worlds is measured in months of programme and in personal criminal liability for dutyholders, so the height survey and the unit count are not paperwork to leave until later. They are the first compliance decision on the job.
Frequently asked questions
- What is a higher-risk building?
- A higher-risk building is a building in England at least 18 metres tall or with at least 7 storeys, containing at least two residential units. Care homes and hospitals meeting the height test are higher-risk at the design and construction stage. The definition sits in the Higher-Risk Buildings (Descriptions and Supplementary Provisions) Regulations 2023.
- Is an 18m office block a higher-risk building?
- No. Height alone is not enough. A building only enters the higher-risk regime for design and construction if it also contains at least two residential units, or is a care home or hospital meeting the height test. A purely commercial office block, however tall, is outside the higher-risk building control regime.
- Do hospitals and care homes count as higher-risk buildings?
- Yes, at the design and construction stage, if they are at least 18 metres tall or have at least 7 storeys. They go through Gateways 2 and 3 with full BSR scrutiny. They are excluded from Gateway 1 at planning, so their design teams carry the planning-stage fire review without a statutory consultee.
- How is the 18 metre height measured?
- Height is measured from ground level to the finished floor level of the top storey, ignoring any storey that is purely plant or machinery. The storey count and the metre measurement are alternative triggers, so a building can qualify on storeys before it reaches 18 metres, or on height with fewer than seven storeys.
Related
This page is information, not legal advice. It is written and maintained by a practitioner, verified against primary sources on the date shown above, and corrected fast when the regime moves. Spotted something out of date? Tell us.