B1.1 The permitted limit of unprotected areas in any side of a building or compartment shall be calculated by reference to the requirements of B2.0.

B1.2 For the purposes of this Annex, the expression "unprotected area" has the meaning ascribed to it by Cl.1.4.110, but in calculating the size of unprotected areas or the permitted limit of unprotected areas, the following provisions shall apply -

a. where any area of an external wall is an unprotected area, only because it has combustible material attached to it as cladding, the area of that unprotected area shall be deemed to be half the area of such cladding;

b. when unprotected openings in the same compartment are recessed at a distance or an angle to the plane of reference, the width of the unprotected opening can be reduced accordingly when projected to the plane of reference based on Table 3 and Table 4. However, such reduction is not applicable to the following:

(1) Concave building profile or the like where a specific point on the receiving panel receives radiation from more than one source. 

(2) When the unprotected opening is along a continuous circular profile where its size and angle cannot be determined.

c. no account shall be taken of any of the following:

(1) an unprotected area which does not exceed 0.1m² and which is not less than 1.5m from any other unprotected area in the same side of the building or compartment (unless that other falls within (3) below);

(2) one or more unprotected areas having an area (or, if more than one, the aggregate area) not exceeding 1m² and not less than 4m from any other unprotected area in the same side of the building or compartment (except any such area as is specified in (1) above);

(3) an unprotected area in any part of an external wall which forms part of a protected shaft;

(4) an unprotected area in the side of a building not divided into compartments, if the area is not less than 28m above any ground adjoining that side of the building.

B2.1 The conditions of this Part of this Annex shall be satisfied if a building or compartment is so situated that no point on the relevant boundary is either between the relevant plane of reference and the side of the building or compartment or at a distance from the relevant plane of reference which is less than the distance specified in the Tables to this Part of this Annex, according to the purpose group of the building or compartment, the dimensions of the enclosing rectangle and the unprotected percentage. Linear interpolation to determine the setback distance using Table 1 & 2 is permitted, provided the unprotected percentage falls between 20% and 100%. 

B2.2 For the purpose of this Part of this Annex:

a. “relevant boundary” means as defined in Cl.1.4.89 and for the purpose of this calculation is either parallel to the side of the building under consideration or at an angle of not more than 80° with that side;

b. “plane of reference” means any vertical plane which touches the side or some part of the side of a building or compartment but which (however far extended) does not pass within the structure of such building or compartment (and for this purpose, any balcony, coping or similar projection shall be deemed not to be part either of that side or of the structure); and the relevant plane of reference shall in each case be taken as that most favourable in that respect to the person erecting the building;

c. “enclosing rectangle” means the smallest rectangle on the relevant plane of reference which would:

(1) enclose all the outer edge of any unprotected area of the building or, if the building is divided into compartments, of the compartment (other than any of an unprotected area which is at an angle of more than 80° to the plane of reference the outer edges being for this purpose projected on the plane of reference by line perpendicular to such plane;

(2) have two horizontal sides; and

(3) have height and width falling within those listed in the Tables to this Part of this Annex.

d. “unprotected percentage” means the percentage of the area of the enclosing rectangle which is equal to the aggregate of the unprotected areas taken into account in calculating the enclosing rectangle and as projected on it.

Table 3

Illustration A (Enlarged)

Table 3 (Cont)

Illustration A (Enlarged)

Updated 2 Sep 2024