8.1 The spread of fire within a building can be restricted by sub-dividing it into compartments separated from one another by walls and/or floors of fire-resisting construction. The object is twofold:
- a. to prevent rapid fire spread which could trap occupants of the building; and
- b. to reduce the chance of fires becoming large, on the basis that large fires are more dangerous, not only to occupants and fire and rescue service personnel, but also to people in the vicinity of the building.
Compartmentation is complementary to provisions made in Sections 2 to 5 for the protection of escape routes and to provisions made in Sections 12 to 14 against the spread of fire between buildings.
8.2 The appropriate degree of sub-division depends on:
- a. the use of and fire load in the building, which affects the potential for fires and the severity of fires, as well as the ease of evacuation;
- b. the height to the floor of the top storey in the building, which is an indication of the ease of evacuation and the ability of the fire and rescue service to intervene effectively; and
- c. the availability of a sprinkler system which affects the growth rate of the fire and may suppress it altogether.
8.3 Sub-division is achieved using compartment walls and compartment floors. The circumstances in which they are needed are given in paragraphs 8.9 to 8.19.
8.4 Provisions for the construction of compartment walls and compartment floors are given in paragraphs 8.20 onwards. These construction provisions vary according to the function of the wall or floor.
Special forms of compartmentation
8.5 Special forms of compartmentation to which particular construction provisions apply, are:
- a. walls common to two or more buildings, see paragraph 8.10;
- b. walls dividing buildings into separated parts, see paragraph 8.11; and
- c. construction enclosing places of special fire hazard, see paragraph 8.12.
8.6 For compartmentation to be effective, there should be continuity at the junctions of the fire-resisting elements enclosing a compartment and any openings from one compartment to another should not present a weakness.
8.7 Spaces that connect compartments, such as stairways and service shafts, need to be protected to restrict fire spread between the compartments and they are termed protected shafts. Any walls or floors bounding a protected shaft are considered to be compartment walls or floors for the purpose of this Approved Document.
Buildings containing one or more atria
8.8 Detailed advice on all issues relating to the incorporation of atria in buildings is given in BS 5588-7:1997. However, it should be noted that for the purposes of Approved Document B, the standard is relevant only where the atrium breaches any compartmentation.
Provision of compartmentation
8.9 Compartment walls and compartment floors should be provided in the circumstances described below, with the proviso that the lowest floor in a building does not need to be constructed as a compartment floor. Paragraphs 8.10 to 8.19 give guidance on the provision of compartmentation in different building types. Information on the construction of compartment walls and compartment floors in different circumstances is given in paragraphs 8.20 to 8.31. Provisions for the protection of openings in compartment walls and compartment floors are given in paragraphs 8.32 to 8.34.
All purpose groups
8.10 A wall common to two or more buildings should be constructed as a compartment wall.
8.11 Parts of a building that are occupied mainly for different purposes should be separated from one another by compartment walls and/or compartment floors. This does not apply where one of the different purposes is ancillary to the other. Refer to Appendix D for guidance on whether a function should be regarded as ancillary or not.
Places of special fire hazard
8.12 Every place of special fire hazard (see Appendix E) should be enclosed with fire-resisting construction; see Table A1, Item 13.
Note: Any such walls and floors are not compartment walls and compartment floors.
8.13 In buildings containing flats, the following should be constructed as compartment walls or compartment floors:
- a. every floor (unless it is within a flat, i.e. between one storey and another within one individual dwelling); and
- b. every wall separating a flat from any other part of the building; and
Note: Any other part of the building does not include an external balcony/deck access.
- c. every wall enclosing a refuse storage chamber.
8.14 Blocks of flats with a floor more than 30m above ground level should be fitted with a sprinkler system in accordance paragraph 0.16.
Note: Sprinklers need only be provided within the individual flats, they are not required in the common areas such as stairs, corridors or landings. For the purposes of this paragraph the limit on the scope of BS 9251:2005 to buildings below 20m in height can be ignored.
Institutional buildings including health care
8.15 All floors should be constructed as compartment floors.
8.16 Paragraphs 3.41 to 3.52 give guidance eon the provisions for compartment walls in care homes utilising progressive horizontal evacuation.
Other residential buildings
8.17 All floors should be constructed as compartment floors.
8.18 The following walls and floors should be constructed as compartment walls and compartment floors in buildings of a nonresidential purpose group (i.e. Office, Shop and Commercial, Assembly and Recreation, Industrial, Storage or Other non-residential):
- a. every wall needed to sub-divide the building to observe the size limits on compartments given in Table 12 (see Diagram 28a);
- b. every floor, if the building or separated part (see paragraph 8.22) of the building, has a storey with a floor at a height of more than 30m above ground level (see Diagram 28b);
- c. the floor of the ground storey if the building has one or more basements (see Diagram 28c), with the exception of small premises (see paragraph 3.1);
- d. the floor of every basement storey (except the lowest floor) if the building, or separated part (see paragraph 8.19), has a basement at a depth of more than 10m below ground level (see Diagram 28d);
- e. if the building forms part of a shopping complex, every wall and floor described in Section 5 of BS 5588-0:1991 Fire precautions in the design, construction and use of buildings, Code of practice for shopping complexes as needing to be constructed to the standard for a compartment wall or compartment floor; and
- f. if the building comprises Shop and Commercial, Industrial or Storage premises, every wall or floor provided to divide a building into separate occupancies, (i.e. spaces used by different organisations whether they fall within the same Purpose Group or not).
Note: See also the provision in paragraph 5.58 for store rooms in shops to be separated from retail areas by fire-resisting construction to the standard given in Table A1.
8.19 In a two storey building in the Shop and Commercial or Industrial Purpose Groups, where the use of the upper storey is ancillary to the use of the ground storey, the ground storey may be treated as a single storey building for fire compartmentation purposes, provided that:
- a. the area of the upper storey does not exceed 20% of the area of the ground storey, or 500m2, whichever is less;
- b. the upper storey is compartmented from the lower one; and
- c. there is a means of escape from the upper storey that is independent of the routes from the lower storey.
Construction of compartment walls and compartment floors
8.20 Every compartment wall and compartment floor should:
- a. form a complete barrier to fire between the compartments they separate; and
- b. have the appropriate fire resistance as indicated in Appendix A, Tables A1 and A2.
Note 1: Timber beams, joists, purlins and rafters may be built into or carried through a masonry or concrete compartment wall if the openings for them are kept as small as practicable and then fire-stopped. If trussed rafters bridge the wall, they should be designed so that failure of any part of the truss due to a fire in one compartment will not cause failure of any part of the truss in another compartment.
Note 2: Where services are incorporated within the construction that could provide a potential source of ignition, care should be taken to ensure the risk of fire developing and spreading prematurely into adjacent compartments is controlled.
Compartment walls between buildings
8.21 Compartment walls that are common to two or more buildings should run the full height of the building in a continuous vertical plane. Thus adjoining buildings should only be separated by walls, not floors.
Separated parts of buildings
8.22 Compartment walls used to form a separated part of a building (so that the separated parts can be assessed independently for the purpose of determining the appropriate standard of fire resistance) should run the full height of the building in a continuous vertical plane. The two separated parts can have different standards of fire resistance.
Other compartment walls
8.23 Compartment walls not described in paragraphs 8.21 and 8.22 should run the full height of the storey in which they are situated.
8.24 Compartment walls in a top storey beneath a roof should be continued through the roof space (see definition of compartment in Appendix E).
Junction of compartment wall or compartment floor with other walls
8.25 Where a compartment wall or compartment floor meets another compartment wall or an external wall, the junction should maintain the fire resistance of the compartmentation. Fire-stopping should meet the provisions of paragraphs 10.17 to 10.19.
8.26 At the junction of a compartment floor with an external wall that has no fire resistance (such as a curtain wall) the external wall should be restrained at floor level to reduce the movement of the wall away from the floor when exposed to fire.
8.27 Compartment walls should be able to accommodate the predicted deflection of the floor above by either:
- a. having a suitable head detail between the wall and the floor, that can deform but maintain integrity when exposed to a fire; or
- b. the wall may be designed to resist the additional vertical load from the floor above as it sags under fire conditions and thus maintain integrity.
Note: Where compartment walls are located within the middle half of a floor between vertical supports, the predicted deflection may be assumed to be 40mm unless a smaller value can be justified by assessment. Outside this area the limit can be reduced linearly to zero at the supports. For steel beams that do not have the required fire resistance, reference should be made to SCI Publication 288 Fire safe design: A new approach to multi-storey steel-framed buildings (Second Edition) 2000 (ISBN: 1 85942 169 5).
Junction of compartment wall with roof
8.28 A compartment wall should be taken up to meet the underside of the roof covering or deck, with fire-stopping where necessary at the wall/roof junction to maintain the continuity of fire resistance. The compartment wall should also be continued across any eaves cavity (see paragraph 8.20a).
8.29 If a fire penetrates a roof near a compartment wall there is a risk that it will spread over the roof to the adjoining compartment. To reduce this risk and subject to paragraph 8.30, a zone of the roof 1500mm wide on either side of the wall should have a covering of designation AA, AB or AC (see Appendix A, paragraph 6) on a substrate or deck of a material of limited combustibility, as set out in Diagram 30a. Note: Thermoplastic rooflights which, by virtue of paragraph 14.7, are regarded as having an AA (National class) designation or BROOF(t4) (European class) classification are not suitable for use in the zone described above.
8.30 In buildings not more than 15m high, of the purpose groups listed below, combustible boarding used as a substrate to the roof covering, wood wool slabs, or timber tiling battens, may be carried over the compartment wall provided that they are fully bedded in mortar or other suitable material over the width of the wall (see Diagram 30b). This applies to, buildings or compartments in Residential use (other than Institutional), Office buildings, Assembly and Recreation buildings.
Note: Double-skinned insulated roof sheeting, with a thermoplastic core, should incorporate a band of material of limited combustibility at least 300mm wide centred over the wall.
8.31 As an alternative to paragraphs 8.29 or 8.30 the compartment wall may be extended up through the roof for a height of at least 375mm above the top surface of the adjoining roof covering. Where there is a height difference of at least 375mm between two roofs or where the roof coverings on either side of the wall are AA, AB or AC this height may be reduced to 200mm (see Diagram 30c).
Openings in compartmentation
Openings in compartment walls separating buildings or occupancies
8.32 Any openings in a compartment wall which is common to two or more buildings, or between different occupancies in the same building, should be limited to those for:
- a. a door which is needed to provide a means of escape in case of fire and which has the same fire resistance as that required for the wall (see Appendix B, Table B1) and is fitted in accordance with the provisions of Appendix B; and
- b. the passage of a pipe which meets the provisions in Section 10.
8.33 Information on fire doors may be found in Appendix B.
Openings in other compartment walls or in compartment floors
8.34 Openings in compartment walls (other than those described in paragraph 8.32) or compartment floors should be limited to those for:
- a. doors which have the appropriate fire resistance given in Appendix B, Table B1 and are fitted in accordance with the provisions of Appendix B;
- b. the passage of pipes, ventilation ducts, service cables, chimneys, appliance ventilation ducts or ducts encasing one or more flue pipes, which meet the provisions in Section 9;
- c. refuse chutes of non-combustible construction;
- d. atria designed in accordance with BS 5588-7:1997; and
- e. protected shafts which meet the relevant provisions below.
8.35 Any stairway or other shaft passing directly from one compartment to another should be enclosed in a protected shaft so as to delay or prevent the spread of fire between compartments.
There are additional provisions in Sections 2 to 5 for protected shafts that are protected stairways and in Section 17 if the stairway also serves as a firefighting stair.
Uses for protected shafts
8.36 The uses of protected shafts should be restricted to stairs, lifts, escalators, chutes, ducts and pipes. Sanitary accommodation and washrooms may be included in protected shafts.
Construction of protected shafts
8.37 The construction enclosing a protected shaft (see Diagram 31) should:
- a. form a complete barrier to fire between the different compartments which the shaft connects;
- b. have the appropriate fire resistance given in Appendix A, Table A1, except for uninsulated glazed screens which meet the provisions of paragraph 8.38; and
- c. satisfy the provisions about their ventilation and the treatment of openings in paragraphs 8.41 and 8.42.
Uninsulated glazed screens to protected shafts
8.38 If the conditions given below and described in Diagram 32 are satisfied, an uninsulated glazed screen may be incorporated in the enclosure to a protected shaft between a stair and a lobby or corridor which is entered from the stair. The conditions to be satisfied are:
- a. the standard of fire resistance for the stair enclosure is not more than 60 minutes; and
- b. the glazed screen:
- i. has at least 30 minutes fire resistance in terms of integrity; and
- ii. meets the guidance in Appendix A, Table A4, on the limits on areas of uninsulated glazing; and
- c. the lobby or corridor is enclosed to at least a 30 minute standard.
8.39 Where the measures in Diagram 32 to protect the lobby or corridor are not provided, the enclosing walls should comply with Appendix A,Table A1 (item 8c) and the doors with the guidance in Appendix A, Table A4.
Pipes for oil or gas and ventilation ducts in protected shafts
8.40 If a protected shaft contains a stair and/or a lift, it should not also contain a pipe conveying oil (other than in the mechanism of a hydraulic lift) or contain a ventilating duct (other than a duct provided for the purposes of pressurizing the stairway to keep it smoke free; or a duct provided solely for ventilating the stairway).
Any pipe carrying natural gas or LPG in such a shaft should be of screwed steel or of all welded steel construction, installed in accordance with the Pipelines Safety Regulations 1996, SI 1996No 825 and the Gas Safety (Installation and use) Regulations 1998, SI 1998 No 2451.
Note: A pipe is not considered to be contained within a protected shaft if the pipe is completely separated from that protected shaft by fireresisting construction.
Ventilation of protected shafts conveying gas
8.41 A protected shaft conveying piped flammable gas should be adequately ventilated direct to the outside air by ventilation openings at high and low level in the shaft.
Any extension of the storey floor into the shaft should not compromise the free movement of air over the entire length of the shaft. Guidance on such shafts, including sizing of the ventilationopenings, is given in BS 8313:1997.
Openings into protected shafts
8.42 Generally an external wall of a protected shaft does not need to have fire resistance.
However, there are some provisions for fire resistance of external walls of firefighting shafts in BS 5588-5:2004, which is the relevant guidance called up by paragraph 17.11 to 17.13 and of external walls to protected stairways (which may also be protected shafts) in paragraph 5.24.
Openings in other parts of the enclosure to a protected shaft should be limited as follows:
- a. Where part of the enclosure to a protected shaft is a wall common to two or more buildings, only the following openings should be made in that wall:
- i. a door which is needed to provide a means of escape in case of fire; and which has the same fire resistance as that required for the wall (see Appendix B, Table B1); and is fitted in accordance with the provisions of Appendix B; and/or
- ii. the passage of a pipe which meets the provisions in Section 10.
- b. Other parts of the enclosure (other than an external wall) should only have openings for:
- i. doors which have the appropriate fire resistance given in Appendix B, Table B1 and are fitted in accordance with the provisions of Appendix B;
- ii. the passage of pipes which meet the provisions in Section 10;
- iii. inlets to, outlets from and openings for a ventilation duct, (if the shaft contains or serves as a ventilating duct) which meet the provisions in Section 10; and/or
- iv. the passage of lift cables into a lift machine room (if the shaft contains a lift). If the machine room is at the bottom of the shaft, the openings should be as small as practicable.