3.5 EXTERNAL WALL
3.5.1 Requirements of external walls
External walls (including any external cladding or internal lining) shall:
a. Be constructed wholly of non-combustible materials.
b. Be so constructed as to attain the fire resistance required by this Code.
3.5.2 Unprotected areas in any side of a station
Unprotected areas in any side of a station shall comply with all the following:
a. Any relevant requirements relating to the permitted limits of unprotected areas specified in Annex 3B unless the station is so situated that such side can in accordance with Annex 3B consists entirely of any unprotected area.
b. The extent of unprotected openings in an external wall of a station in relation to its distance from the lot boundary can be double that which is specified in Annex 3B when the station or compartment is fitted throughout with an automatic sprinkler system in compliance with the requirements in Chapter 6.
c. For the calculations of unprotected areas, platform public areas shall be excluded from the unprotected openings calculation.
d. Where a ground level entrance of an underground station is a single storey structure with no habitable room, the distance ‘X’ between the external wall of the entrance and the external wall of an adjacent building as shown in Diagram 3.5.2d., shall comply with the distance stipulated in Annex 3B based on the extent of unprotected openings in the external wall of the adjacent building.
3.5.3 External wall finishes
Cladding on external walls shall be of non-combustible construction.
3.5.4 Reference to Annex 3B
Any reference to Annex 3B shall be construed as referring to the provisions of B.1 of that Annex together with (at the option of the person intending to erect the station) the provisions of B.2.
3.5.5 Stations on land in common occupation
If two or more detached stations are erected on land in common occupation, any external wall of any station so erected which faces an external wall of such other station, the relevant boundary shall be a notional boundary passing between those stations and such boundary must be capable of being situated in such a position as to enable the external walls of those stations to comply with the require¬ments of Cl.3.5.2.
3.5.6 Vertical fire spread
R Rationale - Clause 3.5.6The purpose of providing high/ low separation is to ensure fire will not spread from the lower compartment to the abutting higher compartment of the station.
For high and low parts of different compartments of a station abutting each other, either one of the following requirements shall be complied with to prevent spread of fire between the distinct parts:
a. The roof over the lower part of the station shall be fire-rated in accordance with the element of structure for minimum 1-hr for a distance of 5m measured horizontally from the external wall of the higher part of station; or
b. The external wall of the higher part of the station overlooking the roof below shall have the necessary fire resistance rating in accordance with the element of structures for minimum 1-hr for a vertical height of not less than 9m measured from the roof of the lower part of the station.