Table 10 sets out maximum dimensions for undivided concealed spaces. With the exceptions given in the rest of this section, extensive concealed spaces should be sub-divided to comply with the dimensions in table 10.

The provisions in table 10 do not apply to any cavity described below:

a. in a wall which should be fire-resisting only because it is loadbearing;

b. in a masonry or concrete external cavity wall shown in figure 31;

c. in any floor or roof cavity above a fire- resisting ceiling, as shown in figure 32 and which extends throughout the building or compartment subject to a 30m limit on the extent of the cavity; or

d. formed behind the external skin of an external cladding system with a masonry or concrete inner leaf at least 75mm thick, or by overcladding an existing masonry (or concrete) external wall, or an existing concrete roof, provided that the cavity does not contain combustible insulation; or

e. between double-skinned corrugated or profiled insulated roof sheeting, if the sheeting is a material of limited combustibility and both surfaces of the insulating layer have a surface spread of flame of at least Class 0 or 1 (National class) or Class C-s3, d2 or better (European class) (see appendix A) and make contact with the inner and outer skins of cladding (see figure 33); or

f. below a floor next to the ground or oversite concrete, if the cavity is less than 1000mm in height or if the cavity is not normally

Notes:

1. Exceptions to these provisions are given in section 6.4.4.1.

2. The national classifications do not automatically equate with the equivalent classifications in the European column, therefore products cannot typically assume a European class unless they have been tested accordingly.

3. When a classification includes ‘s3, d2’, this means that there is no limit set for smoke production and/or flaming droplets/particles.

accessible by persons, unless there are openings in the floor such that it is possible for combustibles to accumulate in the cavity (in which case cavity barriers should be provided and access should be provided to the cavity for cleaning).

Note: When a classification includes ‘s3, d2’, this means that there is no limit set for smoke production and/or flaming droplets/particles.

Where any single room with a ceiling cavity or underfloor service void exceeds the dimensions given in table 10, cavity barriers need only be provided on the line of the enclosing walls/partitions of that room, subject to:

a. the cavity barriers being no more than 40m apart; and

b. the surface of the material/product exposed in the cavity being Class 0 or Class 1 (National class) or Class C-s3, d2 or better (European class).

Note: When a classification includes ‘s3, d2’, this means that there is no limit set for smoke production and/or flaming droplets/particles.

Where the concealed space is an undivided area which exceeds 40m (this may be in both directions on plan) there is no limit to the size of the cavity if:

a. the room and the cavity together are compartmented from the rest of the building;

b. an automatic fire detection and alarm system meeting the relevant recommendations of BS 5839-1:2002 is fitted in the building. Detectors are only required in the cavity to satisfy BS 5839-1;

c. the cavity is used as a plenum and the recommendations about recirculating air distribution systems in BS 5588-9:1999 are followed;

d. the surface of the material/product used in the construction of the cavity which is exposed in the cavity is Class 0 (National class) or Class B-s3, d2 or better (European class) and the supports and fixings in the cavity are of non-combustible construction;

e. the flame spread rating of any pipe insulation system is Class 1 or Class C-s3, d2 or better (European class) (see appendix A);

f. any electrical wiring in the void is laid in metal trays, or in metal conduit; and

g. any other materials in the cavity are of limited combustibility or Class A2 or better (European class) (see appendix A).

Note: When a classification includes ‘s3, d2’, this means that there is no limit set for smoke production and/or flaming droplets/particles.

6.4.4.1 Maximum dimensions of concealed spaces

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