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The provision of minimum two remotely located staircases or other exits provides for alternate escape for the occupants in the event that one staircase or alternate exit is blocked off or rendered unusable during an emergency situation.

Figure 9.2.1a.(2)

The provision of two remotely located staircases or other exits provides for alternate escape for the occupants if one staircase or alternate exit is blocked off or rendered unusable in an emergency situation.

Figure 9.2.1a.(3) - 1

Single staircase is only permitted for buildings not exceeding 4 storeys as the exit staircase is not separately enclosed. The above figure shows a protected lift shaft, which is wrapped around by an exit staircase.

The space between the entrance doors and the lift shaft serves as a staircase landing, lift lobby and entrance to the residential units. It is not considered as a smoke-stop lobby. Buildings, which are not more than 4 storeys, are not required to be provided with smoke-stop lobby. Instead, the residential units have direct entry into the staircase enclosure.

The above arrangement, with or without a protected lift shaft, is not acceptable for buildings exceeding 4 storeys.

The above arrangement is also not acceptable if the staircase is fully enclosed and provided with mechanical ventilation. The reason is that the movement of the lift car could cause a ‘piston effect’ to push or draw smoke into the staircase should a fire occur in the lift car or any of apartment units.

Figure 9.2.1a.(3) - 2

Single exit staircase is permitted in buildings more than 4 storeys and with habitable height not exceeding 24m, if there is smoke-free approach to the exit staircase. This can be achieved by providing a smoke-stop lobby or corridor which is open-sided, in compliance with Cl.2.3.10.

Figure 9.2.1a.(3) - 3

Single exit staircase is permissible in buildings with ‘slab-block’ design and with habitable height not exceeding 24m, if there is an open-sided corridor between the unit and the exit staircase and where the exit staircase is cross-ventilated, provided that the travel distance requirements are complied with.

Not Acceptable

Figure 9.2.1a.(3) - 4

Ventilation of the lobby through private enclosed space is not acceptable.

Not Acceptable

Figure 9.2.1a.(3) - 5

The provision of ventilation shall not be made via private spaces, as such spaces are subject to modification by the unit owner. In order to ensure the permanency of the means of ventilating the smoke-stop lobby, openings for such must always be provided through common areas.

Figure 9.2.1a.(3) - 6 : Protected lobby to single-unit storeys

For single unit per storey design, the smoke-stop lobby or fire lift lobby shall not be converted to other usage. It shall be kept free of any article or furniture. Therefore, it shall be kept as a common area and not be included as part of the strata unit. The lobby area acts as buffer zone against smoke migration into the staircase. The fire lift lobby is required for use by firefighters during fire emergency.

Figure 9.2.1a.(4) : Provision of single staircase for residential building not exceeding 60m in habitable height

Residential buildings not exceeding 60m in habitable height can be provided with single exit staircase, but the approach to exit staircase must be via cross-ventilated lobby. In designing the cross-ventilated lobby, there are instances where building designers only provide the minimum 2m wide and 1.2m high ventilation openings on the opposite ends of the lobby so as to minimize rain water from splashing into the lobby space. There may also be overhang structures at the openings. While the code specifies the minimum opening size for cross ventilation of the lobby, building designers are encouraged to go beyond this specification. A well-designed cross-ventilated lobby that also addresses rain water from splashing into it can be achieved through thoughtful design at the planning stage. Building designers should also note that the protrusion of any overhang structures at the openings shall not exceed 1.4m. Neither should its design be such that it results in a smaller ventilation openings size e.g. a downward sloping overhang.

The minimum size of ventilation openings in a cross-ventilated lobby minimises the risk of the lobby being smoke-logged. These dimensions have been validated through a fire engineering study. 

Figure 9.2.1a.(4)(e) : 

Single exit provision – In a block of residential apartments or maisonettes with habitable height not exceeding 60m, one exit staircase only can be provided to every storey.

The provision of single exit staircase must be seen as a relaxation from the two exit staircases requirement. If only one exit staircase is provided, it is important that the smoke-free approach to the single exit staircase is absolutely maintained at all times. For this concern, the cross ventilation openings to the lobby must be maintained and shall not be blocked or obstructed by air-con condensing unit or other structures that may be introduced to keep rainwater away from the lobby.

Figure 9.2.1a.(5)(a) - 1

The travel distances measured from the most remote point (A) in the unit in Figure 9.2.1a.(5)(a) – 1 to its exit door (B) shall not exceed 20m.

Figure 9.2.1a.(5)(a) - 2

If the travel distance from the most remote point (A) in Figure 9.2.1a.(5)(a) – 2 to the unit’s main exit door (C) exceeds 20m, then a second door (B) to the unit is required. The doors shall be located such that the travel distance from any point in that unit to the nearest exit door (B or C) is within 20m. Where a 2^nd exit from a unit is required, it shall not pass through utility or storeroom.

Figure 9.2.1a.(5)(b) : Exit from maisonette unit

The maisonette unit shall not comprise more than 2 storeys and the main exit shall be located at the main storey. If the upper storey exceeds 60m², there shall be at least one exit door from each storey that have direct access to the exit staircase or exit passageway.

In the single exit situation, the travel distance (ABC in Figure 9.2.1a.(5)(b)), measured from the most remote point in the maisonette (point A on the second level), to the main exit door opening to the corridor (point C), shall not exceed 20m.

Figure 9.2.1a.(6) - 1 

Doors B and C in the above figure are the required exits to Apt.1, as both doors are needed to satisfy the internal travel distances from the remote points A and D.  Hence, the travel distance from Apt.1 to the exit staircase shall be measured from its most remote door to the exit staircase, which is CG.

In the case of Apt.4, the travel distance to the exit staircase shall be taken from Door H.

Figure 9.2.1a.(6) - 2

Where two way escape is available from an apartment in a residential block with multiple exit staircases, e.g. Apt. C in the above figure, each of its doors must be within the desired travel distance to their nearest respective exit staircase.

The purpose of providing a smoke-free approach to an exit staircase is to create an effective buffer for venting of smoke and heat so that occupants can access the staircase safely.

Section

Figure 9.2.1a.(7) - 1 : Part section of residential building
with external corridor

Elevation

Figure 9.2.1a.(7) - 2 : Typical layout of cross-ventilated internal corridor - Exit staircase approached from external corridor

Not Acceptable

Figure 9.2.1a.(7) - 3

Acceptable

Figure 9.2.1a.(7) - 4

Corridors or lobbies, which are cross-ventilated, serve as smoke-free approach to exit staircases from residential units. For effective cross ventilation and quick smoke dispersal from these areas, particular attention must be given during design stage of buildings,  to ensure clear wide open unobstructed paths for the passage of the wind currents as shown in Figure 9.2.1a.(7) – 4. Layout in Figure 9.2.1a.(7) – 3 is not desirable, as the wind path is obstructed, creating a situation whereby smoke build up in the lobby area would be retained for prolonged periods by turbulent eddy wind currents.

Not Acceptable

Figure 9.2.1a.(7) - 5 : Ventilation for smoke-free approach to exit staircases - Example of a 20-storey appartment building

Acceptable

Figure 9.2.1a.(7) - 6

The above design layout (Figure 9.2.1a.(7) – 5), is not favourable as ventilation of the corridors and lobbies through the narrow central court or air well, is not effective for such high-rise development. The staircases are sharing ventilation with other areas via the air wells. The central services cores, which also incorporates the exit staircases and lifts, further disrupt or obstruct any possible wind current through that air well space.

For smoke free approach to exit staircases through air well, open vertically to the sky, the air well shall have a minimum width of 6m and a superficial plan area of not less than 93m².

The above layout could be improved by separating the abutting blocks and widening the width of the internal court as shown in Figure 9.2.1a.(7) - 6.

Figure 9.2.1a.(8)(a)

Figure 9.2.1a.(9)

Cross-ventilated exit staircase of residential apartments or maisonettes, shown in above, should be able to prevent any accumulation of smoke and provide the smoke-free condition for occupants to evacuate. The above clause grants a relaxation of the requirement for 3m separation of unprotected openings from exit staircases, required under Cl.2.3.3, and is only applicable to residential buildings.

Cross ventilation for exit staircases of residential apartments or maisonettes serves to address accumulation of smoke and provide a smoke-free condition for occupants to evacuate.

Figure 9.2.1a.(10)(b)

To address smoke-logged situation that may take place in an internal corridor, a suitable means of ventilation shall be provided. In a case of long internal corridor with units entrance fronting, it shall be provided with cross ventilation. Each end of the wall shall not be less than 50% of the superficial area of the end walls.

Figure 9.2.1b.(1)(b)

Section

Figure 9.2.1b.(2) - 1

a. An attic can be added to new or existing buildings under PG I, provided the total number of storeys or levels in the building does not exceed 4, inclusive of basement.

b. The attic can be constructed of timber boardings on timber joists, provided that it is protected to achieve the fire resistance rating required of the elements of structure of the building.

Section

Figure 9.2.1b.(2) - 2

The above should be seen as a relaxation as timber floors are only allowed in buildings under conservation. Owing to the need to create additional living space in existing houses for extended family use, etc. many applications were received to have addition of attic. In all the applications affecting existing buildings, timber floor construction was the norm for ease of construction and the need to consider the dead load affecting the existing structures. The SCDF had considered the problems of many old houses, which could not be easily and cheaply modified to receive RC floor construction for attic. Under Cl.3.15.3, impregnation of timber boardings and joists for the construction of attic is acceptable.

Illustration for Cl 9.2.1b.(3)(a)

Illustration for Cl 9.2.1b.(3)(b)