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Any reference to a surface being Class 0 shall be construed as a requirement that:

a. the material of which the wall or ceiling is constructed shall be non-combustible throughout, or

b. the surface material (or, if it is bonded throughout to a substrate, the surface material in conjunction with the substrate) shall have a surface of Class 1 when tested to BS 476 Part 7 and if tested in accordance with BS 476: Part 6 shall have an index of performance (I) not exceeding 12 and a sub-index (i₁) not exceeding 6.

Any reference to a surface being of a class other than Class 0, shall be construed as a requirement that the material which the wall or ceiling is constructed shall comply with the relevant test criteria relating to surface spread of flame, which is specified in relation to that class in BS 476: Part 7.

Class 0 shall be regarded as the highest class (based on BS 476 Part 6 & 7), followed in descending order by Class 1, Class 2, Class 3 and Class 4 (based on BS 476 Part 7), as set hereunder:

a. Class 0 - Surface of no flame spread. Such surfaces shall conform to the requirements of Cl.3.13.1.

b. Class 1 - Surface of very low flame spread. This refers to surfaces on which during the first 1½ mins of test, the spread of flame does not exceed 165mm and the final spread of flame does not exceed 165mm under the relevant test conditions.

c. Class 2 - Surface of low flame spread. This refers to surfaces on which during the first 1½ mins of test, the spread of flame does not exceed 215mm and the final spread of flame does not exceed 455mm under the relevant test conditions.

d. Class 3 - Surface of medium flame spread. This refers to surfaces on which during the first 1½ mins of test, the spread of flame does not exceed 265mm and the final spread of flame does not exceed 710mm under the relevant test conditions.

e. Class 4 - Surface of rapid flame spread. This refers to surfaces on which the spread of flame exceeded the limit of Class 3.

The surface of a wall or ceiling in a room/space shall be of a class not lower than specified as relevant in the Table 3.13A, provided that

a. Where an automatic sprinkler system is fitted throughout in the building in compliance with the requirements in Chapter 6, there is no control on the surface of flame rating in rooms/spaces, except for the following occupancies/usage:

(1) healthcare facilities, including hospital, and nursing homes for handicapped, disabled, aged or persons with mental and/or mobility impairments;

(2) detention facilities; and

(3) exit staircases, exit passageways and smoke-free/fire lift lobbies.

b. Where a building is not protected by an automatic sprinkler system, surfaces of the walls and ceilings can be of a surface class not lower than Class 3 to the extent permitted by Cl.3.13.5a. and Cl.3.13.5b. respectively.

c. If timber is used as the surface material for the walls along the side gangways of an auditorium which is not sprinkler-protected, the requirements of this regulation pertaining to the requisite class of flame spread can be relaxed only in respect of those parts of such wall surfaces provided the aggregate area of such parts does not exceed 50% of the whole surface area of the side walls of the auditorium.

a. Any part of the surface of a wall in a room or compartment can be of any class not lower than Class 3 if the area of that part (or if there are two or more such parts, the total area of those parts) does not exceed the following

(1) in the case of a building or compartment of PG III, 20m², or

(2) in any other case, 60m².

b. Any part of the surface of a ceiling can be of any class not lower than Class 3 if that part of the surface is the face of a layer of material the other face of which is exposed to the external air (skylight included) and complies with any one of the following:

(1) The ceiling is that of a room in a building or compartment of PG III, IV, V or VII, or is that of a circulation space excluding a smoke-free lobby, exit staircase or exit passageway in a building or compartment of any purpose group, and

(a) the area of that part does not exceed 2.5m²; and

(b) the distance between that part and any other such part is not less than 3.5m.

(2) The ceiling is that of a room in a building or compartment of PG VI or VIII, and

(a) the area of that part does not exceed 5m²;

(b) the distance between that part and any other such part is not less than 1.8m; and

(c) that part and all other such parts are evenly distributed over the whole area of the ceiling and together have an area which does not exceed 20% of the floor area of the room.

(3) The ceiling is that of a balcony, verandah, open car porch, covered way or loading bay which (regardless of its floor area) has at least one of its longer sides wholly and permanently open.

(4) The ceiling is that of a garage or outbuilding which (regardless of whether it forms part of a building or is a building which is attached to another building or wholly detached) has a floor area not exceeding 40m².

Wall and ceiling finishes in the form of thin sheet of not more than 1.0mm thickness mounted to a non-combustible substrate will not be subject to the requirement of surface spread of flame provisions, except for exit staircases and passageways.