Part G3 Atrium construction
G3.1 Application of Part
This Part does not apply to an atrium which—
connects only 2 storeys; or
To clarify which atriums must comply with Part G3.
Part G3 does not apply to an atrium if it connects two storeys in a non-sprinkler protected building, or up to three storeys if each of the connected storeys is sprinkler protected and one of those storeys is at a level giving egress to a road or open space.
This provision is consistent with D1.12, which deals with the number of floors that can be connected by a non-required non-fire-isolated stairway, ramp or escalator.
G3.2 Dimensions of atrium well
An atrium well must have a width throughout the well that is able to contain a cylinder having a horizontal diameter of not less than 6 m.
To minimise the risk that radiant heat from a fire will affect people or materials on the other side of an atrium well.
An atrium well is not limited to having a maximum size, nor is there a limitation on its shape, except that it must contain a space throughout which could contain a cylinder with a diameter of 6 metres. This 6 metres is equal to the minimum distance between unprotected openings in external walls of adjoining buildings required by C3.2. This diameter void is intended to reduce the effects of radiant heat from a fire:
- affecting occupants evacuating on the other side of the atrium well; and
- igniting materials on the other side of the atrium well.
G3.3 Separation of atrium by bounding walls
An atrium must be separated from the remainder of the building at each storey by bounding walls set back not more than 3.5 m from the perimeter of the atrium well except in the case of the walls at no more than 3 consecutive storeys if—
To minimise the risk of spread of fire and smoke from or to the atrium or other parts of the building.
G3.3 requires the use of bounding walls, which limit the risk of fire and smoke spreading from the atrium to other parts of the building and other parts of the building to the atrium.
The detailed requirements for bounding walls are explained in the Comments on Clause 2.4 of Specification G3.8.
The bounding wall and 3.5 metre setback requirements do not apply where there are three or less consecutive storeys and:
- one of these storeys is located at the level from which direct egress is provided to a road or open space; and
- the total floor area of these storeys is limited to that specified in Table C2.2 (the floor area referred to in G3.3(b) is that of the three storeys, and not the total floor of the atrium).
Figure G3.2 illustrates the location of an atrium’s bounding walls.
G3.4 Construction of bounding walls
Bounding walls must—
be constructed of fixed toughened safety glass, or wired safety glass in non-combustible frames, with—
the walls and doors protected with wall-wetting systems in accordance with Specification G3.8; and
a fire barrier with an FRL of not less than –/60/30 installed in any ceiling spaces above the wall.
To limit the spread of fire between different parts of a building by way of an atrium.
The walls bounding an atrium are not fire walls as defined in the BCA. Therefore, these walls do not create separate fire compartments within a storey of the building. The bounding walls define the extent of the part of the building regarded by the BCA to be an “atrium”. See Figure G3.2.
G3.4 prescribes two options for construction of bounding walls:
- applies where the bounding walls are constructed of materials with a FRL of 60/60/60; or
- applies where the bounding walls are constructed of fixed toughened or wired safety glass in non-combustible frames.
G3.5 Construction at balconies
If a bounding wall separating an atrium from the remainder of the building is set back from the perimeter of the atrium well, a barrier that is imperforate and non-combustible, and not less than 1 m high must be provided.
To maximise the safety of people who have access around an atrium.
To maximise public safety, a barrier is required at the edge of a balcony to an atrium. The barrier must:
- have no openings and be non-combustible, to act as a shield from heat during a fire; and
- have a height of 1 metre—which is consistent with D2.16.
G3.6 Separation at roof
In an atrium—
the roof must have the FRL prescribed in Table 3 of Specification C1.1; or
the roof structure and membrane must be protected by a sprinkler system (other than a FPAA101D or FPAA101H system) complying with Specification E1.5.
To minimise the risk that the roof of an atrium will not remain in place during a fire.
Clause 3 of Specification G3.8 requires smoke extraction through the roof, or near the top of an atrium—this smoke extraction is required to be by mechanical exhaust or by smoke and heat vents.
It is therefore important that the roof remains in place during a fire and not allow the re-circulation of smoke. To achieve this, G3.6 requires:
- the roof to have the FRL required by Table 3 of Specification C1.1;or
- the roof structure and membrane to be protected by a sprinkler system (other than a FPAA101D or FPAA101H system).
The materials used in the roof must comply with:
G3.7 Means of egress
To require that safe egress is available from an atrium.
Although the building may have an effective height of less than 25 metres, two exits are required from any area within an atrium. This is due to the additional fire hazard associated with atriums.
There may be other parts of the BCA which permit buildings to have only a single exit. G3.7 overrides any such provisions insofar as they relate to atriums.
All other aspects of the means of access and egress from an atrium must comply with Section D.
G3.8 Fire and smoke control systems
Sprinkler systems, smoke control, fire detection and alarm systems, and emergency warning and intercom systems must be installed in compliance with Specification G3.8.
To specify the additional fire and smoke control systems required for an atrium.
Because of the additional fire hazard associated with an atrium, special fire and smoke control measures are required to reduce the likelihood of conditions being reached which could endanger the safety of occupants before they have time to evacuate. These measures are set out in Specification G3.8.