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Legend: Explanations & Illustrations Rationale Note Revision history Print

CLAUSE 3.11 CONCEALED SPACES

3.11.1 General provision

R Rationale - Clause 3.11.1

Concealed spaces or cavities in a building provide a ready route or flue for smoke and flame to spread undetected, thus increasing the risk to life safety of occupants in the building. This is particularly so in the case of void spaces above a suspended ceiling, in a roof space or in a raised floor system. Therefore, cavity barriers constructed of fire-rated materials shall be provided to prevent the spread of smoke and fire in the concealed spaces.

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Concealed spaces in a building, such as those within suspended ceilings or raised floors, shall be sub-divided by construction of cavity barriers to restrict the spread of smoke and flames.

3.11.2 Closing the edges of cavities

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Cavity barriers shall be used to close the edges of cavities, edges around openings through a wall, floor and any other part of the construction which contains a cavity and to separate any cavity in a wall, floor or any other part of the construction from any other such cavity.

3.11.3 Interrupting cavities

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If a fire-resistant barrier (such as a compartment wall, floor, ceiling or roof) abuts a cavity (including a roof space), such a barrier shall be extended to sub-divide the cavity to form a complete fire resistant barrier. Such cavity barriers shall be of fire resisting construction at least equal to the provision for that required of the fire resisting barrier.

3.11.4 Sub-division of extensive cavities

Cavities, including roof spaces, unless otherwise permitted, shall be sub-divided so that the maximum distance between cavity barriers shall not exceed the relevant dimensions given under Table 3.11A.

3.11.5 Fire resistance and fixing of cavity barriers

E

Cavity barriers shall be:

a. constructed to provide at least ½-hr fire resistance rating; and

b. tightly fitted to rigid construction or the junctions shall be fire-stopped to comply with the requirements of Cl.3.12.

3.11.6 Openings in cavity barriers

E

A cavity barrier shall have no opening except for:

a. a door which has the same fire resistance rating as the cavity barrier, and are kept closed all the times;

b. a pipe which complies with the provision under Cl.3.9.3;

c. a cable or conduit containing one or more cables;

d. a duct which is fitted with suitably mounted automatic fire damper where it passes through the cavity barrier; and

e. other openings fitted with a suitably mounted fire damper.

3.11.7 Raised floors for fixed stages and display platforms

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The construction of raised floors for fixed stages and display platforms shall comply with the following requirements:

a. the concealed space between the structural floor and raised floor shall not be used for storage;

b. no services or installation shall be permitted within the concealed space other than electrical wiring in conduit in compliance with the requirements of SS CP 5;

c. all sides of the raised floor shall be properly sealed; and

d. the concealed space shall be subdivided by cavity barriers in compliance with the requirements of Cl.3.11.4 and Table 3.11A.

3.11.8 Raised floors with or without accessible panels

The construction of raised floors with or without accessible panels shall comply with all of the following requirements:

a. The supporting structure shall be constructed of non-combustible materials having a melting point of at least 750°C.

b. The concealed space between the structural floor and raised floor shall not be used for storage.

c. No services or installations shall be permitted within the concealed space other than:

(1) electrical wiring in metal conduit and metal trunking in compliance with the requirements of SS CP 5;

(2) communication cables for computer equipment; and

(3) fire protection installations serving the area.

d. Where the raised floor is used as a plenum, requirements in Cl.7.1.4 shall be satisfied.

e. Decking of the raised floor shall be constructed of non-combustible material. Where combustible material is used as core material, if allowed in the case of sprinkler-protected buildings, the top, bottom, all sides and cut edges shall be covered with material with surface property complying with Class 0 (excluding materials for floor finishes). 

f. In the case of raised floors with accessible panels, access sections or panels shall be provided such that all concealed spaces between the structural floor and raised floor are easily accessible.

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g. Openings in the raised floor for entry of electrical cables shall be effectively closed to prevent entry of debris or other combustible material into the concealed spaces.

h. All sides of the raised floor shall be properly sealed.

i. the concealed space shall be subdivided by cavity barriers such that the maximum unobstructed area within the concealed space does not exceed 930m2.

j. Where the concealed space is fitted with an automatic sprinkler system which complies with the requirements in Chapter 6, cavity barriers are not required.

k. For a non-sprinkler-protected building, if the height of the concealed space measured between the top of the structural floor and underside of the raised floor decking exceeds 150mm, it shall be fitted with an automatic smoke detection system complying with requirements of SS CP 10. For a sprinkler-protected building, the concealed space shall be fitted with an automatic smoke detection system as above if its height is between 150mm to 400mm, and automatic sprinkler system if it exceeds 400mm; and

l. Where the height of concealed space measured between the top of the structural floor and the underside of the raised floor decking is less than 50mm, the requirements on provision of cavity barriers shall not be applicable.

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3.11.9 Provision for concealed spaces between floor or roof and suspended ceilings

Provision of cavity barriers within the concealed spaces of suspended ceiling can be exempted provided all of the following requirements are complied with:

a. The concealed space shall not be used for storage.

b. The supporting elements shall be constructed of non-combustible material.

c. The exposed surfaces within the concealed space is of Class 0 flame spread (excluding surfaces of any pipe, cable, conduit or insulation of any pipe).

d. In the case of a detector protected building:

(1) if the concealed space does not exceed 800mm in depth, or

(2) if the concealed space is fitted with detectors which comply with the requirements of Chapter 6.

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e. In the case of a sprinkler-protected building:

(1) if the concealed space does not exceed 400mm in depth, or

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(2) if the concealed space exceeds 400mm and does not exceed 800mm in depth and no combustible material is used within the concealed space, or

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(3) if the concealed space is fitted with an automatic sprinkler system which complies with the requirements of Chapter 6.

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f. In the case of other buildings, the concealed space shall not exceed 800mm in depth.

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3.11.10 Exemption of cavity barriers in ceiling space

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Where the concealed space of suspended ceiling is fitted with an automatic sprinkler system which complies with the requirements in Chapter 6,

a. the concealed space can be exempted from provision of cavity barriers; and

b. combustible materials can be used for the supporting elements and exposed surfaces of materials within the concealed space, provided the ceiling is not situated over an exit passageway, smoke-free lobby or other designated means of escape facilities.

3.11.11 Suspended ceiling over protected areas 

E

The concealed spaces of a suspended ceiling over an exit passageway, smoke-stop lobby, exit staircase or other designated means of escape facilities shall comply with the following:

a. the ceiling supporting elements and the ceiling shall be constructed of non-combustible materials.

b. the exposed surfaces within the concealed space shall be of Class 0 surface flame spread; and

c. where sprinkler system is installed within the concealed spaces at smoke-free lobby/fire lift lobby, the ceiling supporting elements and its exposed surface may have a surface spread of flame not lower than Class 2.

3.11.12 Exemption

Buildings under PG I are not required to comply with the requirements on the provision of cavity barriers in concealed spaces. Residential units in buildings under PG II need not comply with requirements on the provision of cavity barriers in concealed floor and ceiling spaces.