Whether an occupied building is a higher-risk building decides whether it must be registered with the Building Safety Regulator and whether the duties in Part 4 of the Building Safety Act 2022 apply to it. The headline test is in section 65 of the Act. The detail that decides real cases is in the Higher-Risk Buildings (Descriptions and Supplementary Provisions) Regulations 2023.
The headline test
Section 65(1): a higher-risk building is a building in England that
- is at least 18 metres in height or has at least 7 storeys, and
- contains at least 2 residential units.
Height and storeys are alternatives. A building under 18 metres with seven storeys qualifies; so does a building of six storeys that reaches 18 metres.
What is "the building"
Regulation 4 answers this before anything is measured. A free-standing structure is a building; attached structures together are one building — unless they contain an independent section, which is then a building in its own right. An independent section is one with its own access in and out, and no access to the rest of the wider building other than to a part with no residential units (regulation 4(6)). Doors intended only for emergencies or maintenance do not count as access (regulation 4(7)). A terrace of blocks on a shared podium can therefore be one building or several, and the answer changes the height and the storey count.
How height is measured
Regulation 5(1): from ground level to the top of the floor surface of the top storey — not to the roof, and not to the parapet. Where the top storey is not directly above the lowest point of the adjacent ground, regulation 5(2) measures vertically from the lowest part of the ground adjacent to the building to a horizontal projection of that top floor surface. On a sloping site, that lowest point is often well below the front door.
A storey that is a roof-top machinery or plant area, or consists exclusively of roof-top plant rooms, is ignored for height.
Which storeys count
Regulation 6(1) sets aside three kinds of storey:
- any storey below ground level — and a storey is below ground level if any part of the finished surface of its ceiling is below the adjacent ground (regulation 6(3));
- roof-top machinery or plant areas, as for height; and
- a storey consisting of a gallery whose internal floor area is less than 50% of the largest storey vertically above or below it that is not below ground level.
The comparison is with the largest storey vertically above or below the gallery that is not below ground level — not simply the floor it sits on.
Galleries and mezzanines. The regulation excuses galleries. It does not use the word mezzanine. The Government guidance treats the two as the same: “Gallery floors may also be known as mezzanines. … Mezzanines are intermediate areas that do not cover the whole length of the building between two main storeys.” On that reading, any part floor under 50% drops out of the count, enclosed or not. On the words of the regulation, a gallery is open to the floor below — Approved Document B defines it as “a floor or balcony that does not extend across the full extent of a building’s footprint and is open to the floor below” — and an enclosed mezzanine is not a gallery, so it counts as a storey whatever its size. Guidance is not law, and the point is untested.
Measuring the floor area. Neither the Act nor the regulations say how “internal floor area” is measured. The RICS Code of Measuring Practice gives two answers for floor under a low ceiling: Gross Internal Area includes floor with less than 1.5 m headroom; Net Internal Area leaves it out. For a gallery in a roof space under sloping ceilings, the choice can decide the result. Measured over the full floor, the gallery is larger and more likely to reach 50%. Measured only where the headroom is at least 1.5 m, it is smaller and more likely to drop out of the count. Whichever basis is chosen must be used for the gallery and for the storey it is compared with.
Plant is only ignored when it is on the roof. An intermediate plant floor is a storey like any other. And where an independent section is treated as a building, regulation 6(2) counts any storey directly beneath it that is not below ground level — so a podium counts in the storey total of the block above it.
Buildings that are excluded
For occupied buildings under section 65, regulation 8 excludes buildings consisting entirely of a care home, a hospital, a secure residential institution, a hotel, military barracks or Ministry of Defence living accommodation, and mixed-use buildings in which all the living accommodation is provided by the Ministry of Defence. A building that is partly hotel and partly flats is not excluded.
Registration
The principal accountable person for an occupied higher-risk building must have it registered with the regulator under section 78. Section 77 makes it an offence for the building to be occupied but not registered, with a defence of reasonable excuse.
The regulator registers a building on the application of the principal accountable person. Where the regulations leave a point open — whether an upper level is a gallery, how internal floor area is measured, whether a section is independent — it is the applicant who has to take a position and state it. The decision on how the building is described is the owner's, made on the facts, and it is worth having it measured and recorded properly before the application, not after a question is asked.
Three things to check first
- Is it one building or several under regulation 4?
- The height from the lowest adjacent ground to the top storey's floor surface, roof-top plant ignored.
- A storey count that has dealt expressly with basements, roof-top plant, galleries and mezzanines, the basis on which floor area is measured, and any podium.