Criteria for determining whether a new building that is being designed and constructed is a "higher-risk building"
Source: gov.uk (2025-05-28)

This guidance relates to the legal criteria for determining whether a proposed new building is considered a higher-risk building under the Building Act 1984 (as amended by the Building Safety Act 2022) and the Higher-Risk Buildings (Descriptions and Supplementary Provisions) Regulations 2023.

Following the initial statement (https://buildingsafety.campaign.gov.uk/building-safety-regulator-making-buildings-safer/building-safety-regulator-news/mhclg-and-bsr-reviewing-first-tier-tribunal-on-classification-of-roof-gardens/) dated 18 October 2024, the Ministry of Housing, Communities and Local Government has carefully considered the views expressed by the Tribunal in the First-tier Tribunal decision (https://www.gov.uk/residential-property-tribunal-decisions/smoke-house-and-curing-house-18-remus-road-london-e3-2nf-lon-slash-00bg-slash-hyi-slash-2023-slash-0024) dated 3 July 2024.

The department recognises the need to provide clarity within the legislation. We are consulting the Building Safety Regulator and other relevant stakeholders on a proposal to amend the Higher-Risk Buildings (Descriptions and Supplementary Provisions) Regulations 2023 to make it clear that roof gardens should not be considered a storey when determining whether a building is a higher-risk building under section 120D of the Building Act 1984 and section 65 of the Building Safety Act 2022.

In the meantime, the department’s view remains that roof gardens are not storeys for these purposes. This is the basis for current government guidance (https://www.gov.uk/government/collections/guidance-on-the-criteria-for-being-a-higher-risk-building), which the sector and regulatory bodies should continue to refer to.

Introduction

This guidance sets out how to determine whether a new building that is being designed and constructed is a “higher-risk building”. For building work to an existing building which will make it a higher-risk building (for example adding storeys) or for a building undergoing a change of use, see the guidance on the criteria for being considered a higher-risk building during building work in an existing building. Higher-risk buildings are subject to the requirements of the new higher-risk regime directly overseen by the Building Safety Regulator (the Regulator).

Higher-risk buildings, for the design and construction requirements, are defined in both Section 120D of the Building Act 1984 (the 1984 Act) as amended by the Building Safety Act 2022 (the 2022 Act) and the Higher-Risk Buildings (Descriptions and Supplementary Provisions) Regulations 2023 (the Regulations).

To understand whether a proposed new building is a higher-risk building, the 1984 Act as amended by the 2022 Act, and the Regulations need to be considered together.

For the design and construction part of the regime, higher-risk buildings are defined as buildings with at least two residential units, care homes, and hospitals which are at least 18 metres in height or have at least 7 storeys. This definition does not amend definitions of higher-risk buildings in other legislations - for example, the definition for higher-risk buildings in occupation (section 65 of the 2022 Act), which can be found here. Sections 119 to 125 and Schedule 8 of the 2022 Act define “relevant building” for the purpose of leaseholder protections.

This guidance document sets out 3 main criteria for consideration and includes the relevant text from the 1984 Act as amended by the 2022 Act and from the Regulations with explanations and diagrams. It is a tool to help potential dutyholders (that is, the client, designer, principal designer, contractor, and principal contractor) determine if the proposed new building will be a higher-risk building. This guidance should be used over other guidance covering buildings, height measurements and/or storey measurements to determine whether the definition of higher-risk building set out is law applies to your building. This guidance and the specific circumstances of your building need to be considered by you when discharging your duties under the building regulations.

Diagrams in this guidance document show examples of potential buildings and are for illustrative purposes only. You will need to consider the legislation carefully to understand whether you are responsible for a proposed higher-risk building in the scope of the higher-risk regime. You may wish to seek legal advice on this.

The definitions of key terms in this guidance can be found in the Glossary.

Guidance for understanding whether your proposed new building is a higher-risk building in the design and construction phase of the regime

Key criteria to consider when determining if a proposed new building is higher-risk includes:

1. Use criteria: What will my proposed new building be used for? Does it meet any of the included or excluded categories of building?

2. Legal definition of building: How does the building definition in Regulations apply to my proposed new building structure?

3. Height and storeys: How do the methods for measuring height and storeys in the Regulations apply to my proposed new building? Does my proposed new building meet either the 18-metre or 7-storey height threshold when measured using these methods?

You will need to consider all 3 criteria.

Use criteria

To be considered a higher-risk building during the design and construction phase of the regime, a proposed new building must meet a certain set of use criteria. This is in addition to meeting the height or storeys threshold.

If a proposed new building meets the height or storeys threshold and contains at least two residential units, is or contains a hospital or a care home, then it is a higher-risk building. This applies unless the entire building is used as a secure residential institution, hotel, or military barracks, or if the building contains any living accommodation provided by the Ministry of Defence for military personnel. These buildings are explicitly excluded.

Use criteria for proposed new buildings in the design and construction phase under the Building Act 1984 and the Higher-Risk Buildings (Descriptions and Supplementary Provisions) Regulations 2023

Section 120D of the Building Act 1984 sets out the buildings which are included in the design and construction part of the higher-risk regime.

120D. Meaning of “higher-risk building” etc

(2) “Higher-risk building” means a building in England that—

(a) is at least 18 metres in height or has at least 7 storeys, and

(b) is of a description specified in regulations made by the Secretary of State.

Regulation 2 of the Higher-Risk Buildings (Descriptions and Supplementary Provisions) Regulations 2023 sets out the buildings which are included in the design and construction part of the higher-risk regime.

2. Specified descriptions of building under section 120D of the Building Act 1984

(2) The following descriptions of building are specified for the purposes of section 120D(2)(b) of the 1984 Act—

(a) a building which contains at least two residential units;

(b) a care home;

(c) a hospital.

Regulation 7 sets out the buildings which are excluded from the design and construction part of the higher-risk regime.
- (1) For the purposes of section 120D of the 1984 Act a “higher-risk building” does not include a building of a description specified in paragraph (2).
(2) The following descriptions of building are specified for the purposes of paragraph (1) (a) a building that comprises entirely of—

(i) a secure residential institution;

(ii) a hotel;

(iii) military barracks;

(b) a building that contains living accommodation provided by the Ministry of Defence (either alone or in combination with other accommodation);

(c) a building that contains living accommodation (either alone or in combination with other accommodation) for—

(i) His Majesty’s forces;

(ii) any visiting force or an international headquarters or defence organisation designated for the purposes of the International Headquarters and Defence Organisations Act 1964.

This means that new buildings which are proposed to be mixed-use but will contain one or more of the included uses and meet the height or storey threshold are subject to the requirements of the higher-risk regime. For example, if a proposed new building contains a shopping centre but also has two or more residential units, then it is a higher-risk building, provided it meets the height or storeys threshold. Proposed new buildings which are designed to be boarding accommodation in schools and university accommodation would also be considered higher-risk buildings, provided they meet the height or storeys threshold for a higher-risk building, as they contain residential units.

New buildings that will contain supported and sheltered accommodation are considered higher-risk buildings if they meet the height or storeys threshold, as they contain residential units. Examples of supported and sheltered accommodation which could fall under the higher-risk regime include domestic abuse refuges, children’s homes and supported or sheltered homes for older people and those with additional care needs.

Residential unit

A residential unit is a dwelling or any other unit of living accommodation and is defined in the Regulations.

Examples of a residential unit are a flat, a studio flat, a home of multiple occupation, shared accommodation within university halls (e.g. a bedroom with shared kitchen and bathroom) or a unit within a supported accommodation building.

A residential unit can be found within any type of building and could have any tenure. Privately owned, private rented and social rented units are all considered residential units under the higher-risk regime.

Care homes and hospitals

Care homes provide accommodation, together with nursing or personal care, for those who are or have been ill, mentally unwell, or dependent on alcohol or drugs or who are disabled or infirm.

Hospitals are institutions for receiving and treating those who are ill, convalescing or need medical rehabilitation, or a maternity home.

Buildings used for receiving and treating those who are ill, convalescing or need medical rehabilitation, or a maternity home without at least one bed for an overnight stay are not considered hospitals under the higher-risk regime. For example, a general practitioner surgery which does not allow overnight stays would not meet the definition of a hospital.

Exclusions

Secure residential institutions

New buildings proposed to be used entirely as secure residential institutions are excluded from the higher-risk regime. Secure residential institutions include prisons, young offenders’ institutions, detention centres, secure training centres, custody centres, short-term holding centres and secure local authority accommodation. If a proposed building is used entirely for one of these purposes, then it is not a higher-risk building.

Hotels and other serviced accommodation

New buildings proposed to be used entirely as hotels are excluded from the higher-risk regime. Hotels are buildings which provide overnight accommodation for customers who stay for the purpose of leisure or business.

We consider hostels which also provide overnight accommodation to customers for leisure or business as a type of hotel and so if a building is used entirely as this type of hostel, then it is not considered a higher-risk building. Hotels are excluded regardless of how long these buildings are occupied by individuals or groups of customers.

Serviced apartments do not fall within the meaning of hotel and are considered higher-risk buildings if they meet the height or storeys threshold.

A short-term let (for example, a short-term rental property let online) is considered a residential unit. If there was another residential unit within the building and the height or storeys threshold was met then the entire building, including the short-term let property, would be considered a higher-risk building.

Military premises

New buildings proposed to be used exclusively as military barracks are excluded from the higher-risk regime.

New buildings proposed to contain any living accommodation either for His Majesty’s forces, any visiting forces or an international headquarters or defence organisation are also excluded.

Building definition

A building for the purposes of the higher-risk regime is defined in Regulation 4 of the Regulations. The diagrams in this section will help you determine how Regulation 4 applies to your proposed building.

Legal definition of a building in the Higher-Risk Buildings (Descriptions and Supplementary Provisions) Regulations 2023

Regulation 4 sets out the definition of a building.

(1) Subject to paragraph (2), where a structure is not attached to any other structure, that structure is a “building”.

(2) Subject to paragraph (5), where a structure that is not attached to any other structure contains one or more independent sections, each independent section is a “building”.

(3) Subject to paragraph (4), where two or more structures are attached, that set of structures are a “building”.

(4) Subject to paragraph (5), where two or more structures that are attached contains one or more independent sections, each independent section is a “building”.

(5) Paragraphs (2) and (4) do not apply while a building is being constructed or proposed to be constructed.

(6) An “independent section” is a section that—

(a) has access, which can be reached from anywhere in the section, for persons to enter and exit the wider building; and

(b) either—

(i) has no access to any other section of the wider building; or

(ii) only has access to another section of the wider building which does not contain a residential unit.

(7) “Access” means a doorway, archway or similar opening but does not include a doorway, archway or similar opening intended for exceptional use including emergency use or use for the purpose of maintenance.

(8) The “wider building” means—

(a) in relation to a section of a structure that is not attached to any other structure, that structure;

(b) in relation to a section within two or more structures that are attached, that set of structures.

(9) Where a section is a “building” pursuant to paragraphs (2) or (4), any plant room containing equipment for the provision of services to that section is to be considered as part of that building.

Under Regulation 4, a proposed building which consists of multiple attached structures is considered one overall structure (one building). You will then need to assess whether it is also a higher-risk building against the height or storeys threshold and use criteria.

For the design and construction of new buildings, an overall structure cannot be split into independent sections. Where a proposed building comprises multiple attached structures, those multiple structures joined together are collectively one higher-risk building. This means a higher-risk building may be a wider development or complex. This is the case even when one or more attached structures do not meet the height or number of storeys or use criteria. Provided the height or storeys threshold and the use criteria are met within the overall set of structures, then the overall set of structures is a higher-risk building. Once the proposed building is complete, you may be able to split the overall structure into independent sections for the occupation part of the higher-risk regime. Please refer to the guidance on the criteria for a higher-risk building during occupation (https://www.gov.uk/guidance/criteria-for-being-a-higher-risk-building-during-the-occupation-phase-of-the-new-higher-risk-regime)

Example buildings defined under the building definition

Diagrams 1 - 3 set out examples of different building types and how they should be considered under the definition in the Regulations. These examples are included to help you assess your proposed building; however, they are illustrative and do not represent all building types.

Diagram 1 shows a proposed new 7-storey residential tower (tower 1A) that is not attached to any other structure. Tower 1A is considered one building.

Diagram 2 shows a proposed new building consisting of multiple attached residential structures of varying storeys. Tower 2A and tower 2B are joined by a shared car park. Tower 2B and tower 2C are attached by walkways. Tower 2C and 2D are attached by a party wall. Area 2E is within tower 2D. For the purpose of designing and constructing a new building, the towers 2A, 2B, 2C and 2D and area 2E are considered one overall structure and therefore one ‘building’.

Tower 2A and tower 2C meet the number of storeys threshold and meet the use criteria as it contains at least two residential units. Therefore, the overall set of structures is considered a single higher-risk building.

Diagram 3 shows a proposed new building consisting of one 7-storey residential tower and one 5-storey residential tower with shared foundations. Tower 3A and 3B are attached at foundation level. For the purpose of designing and constructing a new building, tower 3A and tower 3B are considered one overall structure and therefore one ‘building’.

Counting storeys and measuring height

For a proposed new building to be a higher-risk building, it needs to meet either the height or storeys threshold – it does not need to meet both (although it may). The height threshold is set at 18 metres or higher. The storeys threshold is set at 7 storeys or more.

If a proposed new building meets the 7-storey threshold and meets the use criteria set out in this guidance, then it is a higher-risk building and does not need to be measured against the height threshold. If the proposed new building is 18 meters in height and meets the use criteria, then it is a higher-risk building and does not need to meet the storeys threshold.

If a proposed new building does not meet either the 18-metre or 7-storey height thresholds (for example, it is 17 metres and 6 storeys in height), then it is not a higher-risk building, regardless of whether it meets the use criteria.

Prescribed method for measuring height and counting storeys in the Higher-Risk Buildings (Descriptions and Supplementary Provisions) Regulations 2023 Regulation 5 sets out the method for measuring height.

(1) Subject to paragraph (2), the height of a building is to be measured from ground level to the top of the floor surface of the top storey of the building (ignoring any storey which is a roof-top machinery or roof-top plant area or consists exclusively of roof-top machinery or roof-top plant rooms).

(2) Where the top storey is not directly above the lowest part of the surface of the ground adjacent to the building, the height of the building is to be measured vertically from the lowest part of the surface of the ground adjacent to the building to the point which is a horizontal projection from the top of the floor surface of the top storey of the building (ignoring any storey which is a roof-top machinery or roof-top plant area or consists exclusively of roof-top machinery or roof-top plant rooms).

Regulation 6 sets out the method for counting storeys.
- — (1) Subject to paragraph (2), when determining the number of storeys a building has the following is to be ignored—
(a) any storey which is below ground level;

(b) any storey which is a roof-top machinery or roof-top plant area or consists exclusively of roof-top machinery or roof-top plant rooms; and

(c) any storey consisting of a gallery with an internal floor area that is less than 50% of the internal floor area of the largest storey vertically above or below it which is not below ground level.

(2) Where a section is a building pursuant to regulation 4(2) or (4), any storey directly beneath the building which is not below ground level is to be counted in determining the number of storeys the building has.

(3) A storey is treated as below ground level if any part of the finished surface of the ceiling of the storey is below the ground level immediately adjacent to that part of the building.

Regulation 1(3) defines ground level for these Regulations.

“ground level”, in relation to a building, means—

(a) where the level of the surface of the ground on which the building is situated is uniform, the level of the surface of the ground immediately adjacent to the building; or

(b) where the level of the surface of the ground on which the building is situated is not uniform, the level of the lowest part of the surface of the ground adjacent to the building.

Storeys should be counted from the proposed storey at ground level to the top storey. Height should be measured from ground level to the top of the proposed floor surface of the top storey of the building. The method set out in this guidance should be used when determining whether your proposed building is a higher-risk building, rather than methods set out in other documents.

Ground level

When counting storeys and measuring height, you should measure from ground level. You will need to carefully consider where ground level is for your proposed building. There may be situations in which small spaces have been created adjacent to the proposed building below the level of normal ground floor access such as lightwells. It is unlikely to be appropriate to consider such areas for the purpose of identifying ground level.

If the proposed building being measured sits on uniform flat ground, then ground level is the surface of the ground which is directly adjacent to the building. This is demonstrated in Diagram 4.

Where a proposed building sits on uniform flat ground, when counting storeys, any storeys which are below ground level should not be counted. A storey is considered below ground level and should not be counted if any part of the storey’s finished ceiling is below ground level for the building. Similarly, when measuring height, parts of the building which are below ground level are not measured. This is demonstrated in Diagram 4.

Diagram 4 shows one 7-storey tower.

For the proposed building shown in Diagram 4, storeys should be measured from the first storey above ground level, as indicated by the arrow on the left. The storey below ground level should not be counted. Height should be measured from ground level to the proposed floor surface of the top storey, as indicated by the arrow on the right. For the proposed building shown in Diagram 4, based on the method for counting storeys in the Regulations, this proposed structure is 7 storeys.

When counting storeys and measuring height, if the proposed building being measured sits on uneven ground (for example, a sloping area), then ground level is the lowest part of the ground which touches the proposed building. This is demonstrated in Diagram 5.

Diagram 5 shows a 7-storey residential tower on sloped ground.

In this example, height should be measured from the lowest level of the ground directly adjacent to the structure, as indicated by the arrow. Storeys should be counted from the first storey above ground level. The first storey in the proposed building in Diagram 5 would not be considered below ground level as no part of its finished ceiling is below ground level for the overall building.

In this example, based on the method for counting storeys in the Regulations, this proposed structure is 7 storeys.

Roof-tops

When counting the storeys of a proposed building, any storeys which contain exclusively rooftop machinery or rooftop plant rooms should not be counted. Rooftop machinery is machinery which provides services to the building (for example, an air-conditioning system). Plant rooms are areas which contain machinery or equipment that provides services to the building. Only rooftop plant rooms and areas made up exclusively of rooftop machinery are excluded - for example, if floor 3 of a 7-storey building contained exclusively plant rooms and machinery, it should still be counted as a storey.

A storey must be fully enclosed to be considered a storey. The roof of a proposed building should not be counted as a separate storey. Open rooftops such as rooftop gardens are not considered storeys and should not be counted as such when determining the number of storeys or measuring the height.

When measuring the height of a proposed building, the building should be measured up to the top of the floor surface of the top storey, that is not exclusively rooftop machinery or plant rooms. This is demonstrated in Diagram 6.

Diagram 6 shows a 6-storey residential tower with a rooftop garden.

In this example, height should be measured to the proposed floor surface of the top storey, as indicated by the arrow. The rooftop garden is not considered a storey, so the floor level of the roof should not be measured. Storeys should be counted from the first storey above ground. The proposed building in Diagram 6 has 6 storeys.

If the top storey is exclusively rooftop machinery or plant rooms, then the height of the proposed building should be measured to the top floor surface of the storey below. This is demonstrated in Diagram 7.

Diagram 7 shows a 7-storey residential tower on sloped ground with a rooftop plant room.

In this example, height should be measured from ground level to the proposed floor surface of the top storey, which is not a plant room, as indicated by the arrow. Storeys should be counted from the first storey above ground level. The first storey in this proposed building would not be considered below ground level as part of the finished ceiling of the storey is above ground level for the building.

Based on the method for counting storeys in the Regulations, this building is considered 7 storeys and is a higher-risk building as it contains two or more residential units.

Gallery floors

Some proposed buildings may have gallery floors. Gallery floors may also be known as mezzanines. A mezzanine is an internal area within a building. Mezzanines are intermediate areas that do not cover the whole area of the building between two main storeys.

Diagram 8 shows one 7-storey residential tower with a gallery floor that has a floor area over 50% of the storey above it.

Gallery floors should only be counted as a storey if the internal floor area of the planned gallery floor is at least 50% of the internal floor area of the largest above-ground storey above or below the gallery floor. Once a gallery floor meets the 50% threshold, it will become a storey and should be counted as such. For example, if a proposed gallery floor, forming the first storey of a building, has an internal floor area half the area, or more, of the largest other storey, then this gallery floor should be counted as a separate storey. If the gallery floor is smaller than half the area of the largest storey, then it should not be counted as a separate storey. An example of how gallery floors should be counted is given in Diagram 8.

In this example, the gallery floor’s internal floor area is greater than 50% of the internal floor area of the storeys above it. Based on the method for counting storeys in the Regulations, the gallery floor in this proposed structure would be considered a storey, and the building is considered 7 storeys.

Multiple structures

When counting storeys and measuring height, if the proposed building consists of multiple structures, the storeys should be counted from the ground level (the lowest part of the ground that touches the proposed building) to the highest point of the overall attached structures. Similarly, height should be measured from ground level to the proposed floor surface of the top storey of the overall structure. The tallest part of the building may not be directly above the ground level where storeys start being counted from, and the height measurement starts. An example of this is if the proposed multiple structures are built on a slope. This is demonstrated in Diagram 9.

Diagram 9 shows a 4-storey residential tower attached to a 8-storey residential tower via a party wall on sloped ground.

In this example, based on the method for counting storeys in the Regulations, the proposed building is considered 8 storeys.

Glossary of key terms used in this guidance

The Building Safety Act 2022 (the 2022 Act) was granted Royal Assent on 28 April 2022. It implements the recommendations made in Dame Judith Hackitt’s Building a Safer Future report to create a new more stringent regulatory system for higher-risk buildings. Her recommendations set out clear duties and responsibilities for those who commission, design, construct and refurbish higher-risk buildings, and those who are responsible for making sure that buildings are safely managed when occupied. The 2022 Act is available at the Building Safety Act 2022 (https://www.legislation.gov.uk/ukpga/2022/30/contents/enacted).

The Building Safety Regulator (the Regulator) is charged with improving the safety and standard of buildings through three critical functions:
- leading the delivery of the new regulatory regime for higher-risk buildings;
- overseeing the safety and standards of all buildings; and
- facilitating improvement in the competence of industry and building inspectors.
Care homes provide accommodation, together with nursing or personal care, for those who are or have been ill, mentally unwell or dependent on alcohol or drugs or who are disabled or infirm.

Dutyholders in the design and construction phase of the higher-risk regime are the client, designer, principal designer, contractor, and principal contractor.

They will need to:
- plan, manage and monitor the design work and the building work they undertake to ensure the building work complies with all relevant building regulations.
- cooperate and communicate with other dutyholders (e.g. share information, have effective routes of communication), coordinate their work, and have systems in place to ensure that building work, including design work, complies with all relevant building regulations.
They will also need to be competent (have the right skills, knowledge, experience, and behaviours) for the work they are engaged to do and ensure that those they appoint are also competent to carry out that work.

Higher-risk building is the technical term for buildings within the scope of the higher-risk regime. This guidance is designed to help users understand whether a proposed new building meets the criteria to be considered a higher-risk building under the design and construction part of the regime.

The Higher-Risk Buildings (Descriptions and Supplementary Provisions) Regulations 2023 (the Regulations) are the regulations which build on the provisions in the Act to complete the legal definition of higher-risk building. These are available at The Higher-Risk Buildings (Descriptions and Supplementary Provisions) Regulations 2023 (https://www.legislation.gov.uk/uksi/2023/275/contents/made).

Hospitals are institutions with overnight accommodation for treating those who are ill, convalescing or need medical rehabilitation, or a maternity home.

Overall structure is referred to as ‘wider building’ in the Regulations. If two or more structures are attached, the overall structure refers to all the attached structures. When a structure is not attached to any other structure, the overall structure means that single structure.

A plant room is an area which contains machinery or equipment that provides services to the building.

A resident is a person who resides in a residential unit, regardless of tenure.

A residential unit is a dwelling or any other unit of living accommodation. Examples are a flat, studio flat, shared accommodation within university halls or a unit within a supported accommodation building.

Rooftop machinery is machinery located on the roof of a building which provides services to the building.

Structure is defined in Regulation 1(3) of the Higher-Risk Buildings (Descriptions and Supplementary Provisions) Regulations 2023 as a roofed construction with walls.