Section 118, Building Safety Act 2022 – Section 117: height of buildings and number of storeys

(1) This section applies for the purpose of section 117.

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

(3) When determining the number of storeys in a building—

(a) any storey below ground level is to be disregarded;

(b) any mezzanine floor is to be regarded as a storey if its internal floor area is at least half of the internal floor area of the largest storey in the building which is not below ground

(4) In subsection (2) “ground level”, in relation to a building, means—

(a) 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 immediately adjacent to

(5) For the purposes of subsection (3) a storey is “below ground level” if any part of the finished surface of the ceiling of the storey is below the level of the surface of the ground immediately adjacent to that part of the building.

28 June 2022

England and Wales

A quick reminder – by section 117, a “relevant building” is a building that is either at least 11 metres high or has at least 5 storeys.

This section, 118, describes how a building is to be measured for the purposes of section 117.

Let’s start with “ground level” and work our way up.

Subsection (4) essentially defines “ground level” as the lowest level of the surface of the ground immediately adjacent to the building. So if a building is on a slope, it is the surface of the lowest part of the slope.

So far, so logical.

The top of the building is not however what the mythical person on the Clapham omnibus might expect, because by subsection (2), the measurement is taken from ground level to the “finished surface of the floor of the top storey of the building…”

In other words, the height of the building is not taken to the actual top of the building, but the height of the highest floor surface in that building.

Excluded from that measurement is any storey which is “a roof-top machinery or plant area or consists exclusively of machinery or plant rooms”.

I assume, given the context, that the phrase “or consists exclusively of machinery or plant rooms” is intended to mean “any roof-top storey that consists…”. It is not entirely clear however that other storeys consisting exclusively of machinery or plant rooms are not within the scope of subsection (2). .

So far as I can work out, the measurement is taken from Diagram D6 of Approved Document B (“Height of top storey in building”), rather than from Diagram D4 of the same document (“Height of building”). You can see a copy of Diagram D6 below.

It will be familiar to those involved in applications to the Building Safety Fund for the remediation of non-ACM cladding systems, because it appears in Annex A (Technical Information) of the registration prospectus for applications to that fund.

It is worth noting however that whereas applications for funding allow a 30cm tolerance, no tolerance is given here.

The alternative to getting out the tape measure is to count the number of storeys in the building.

Storeys below ground

Subsection (3) excludes storeys “below ground level”.

Subsection (5) explains what is meant by that phrase. A storey is below ground level if “any part of the finished surface of the ceiling of the storey is below the level of the surface of the ground immediately adjacent to that part of the building”.

Looking at the phrase in context and taking the example of a building on a slope, that means a storey will count towards the statutory five if any part of the finished surface of the ceiling – presumably something like plaster or plasterboard – that is above the level of the ground immediately adjacent to it.

It is not therefore a question of scouting around the outside of the building for ground that is above that ceiling surface: the ceiling surface must be above the ground right next door to the building.

Mezzanine floors

These are more complicated.

By subsection (3)(b) the size of the mezzanine must be compared with the size of the largest storey in the building.

To count as a storey, the mezzanine must be at least of the “internal floor area” of that largest storey on or above ground level. Storeys below ground level, whatever their size, do not count.