NCC 2022 Volume One - Building Code of Australia Class 2 to 9 buildings
Building class 1a Building class 1b Building class 2 Building class 3 Building class 4 Building class 5 Building class 6 Building class 7a Building class 7b Building class 8 Building class 9a Building class 9b Building class 9c Building class 10a Building class 10b Building class 10c


Building class 1a Building class 1b Building class 2 Building class 3 Building class 4 Building class 5 Building class 6 Building class 7a Building class 7b Building class 8 Building class 9a Building class 9b Building class 9c Building class 10a Building class 10b Building class 10c


Part G4 Construction in alpine areas

Part G4 Construction in alpine areas

Accident potential from combustion heaters: Due to the extreme cold, the use of open-fire places and other heating devices is common. This increases the potential for accidents and the possibility of fire. Sub-zero temperatures: Buildings constructed in alpine areas need special consideration because of sub-zero temperatures. The temperatures can create elements which restrict free movement to and from the building. They can also complicate the role of fire brigades and other emergency services. Alpine areas: Part G4 only applies in “alpine areas”. In NSW, ACT and Victoria this means areas more than 1200 metres above Australian Height Datum (AHD). In Tasmania, it is more than 900 metres above the AHD.

Introduction to this Part

This Part contains additional requirements for buildings constructed in an alpine area to address the potential for snow and ice to obstruct or delay evacuation and fire fighting or cause a hazard by falling on people.


The Objective of this Part is to safeguard occupants in alpine areas from illness or injury from an emergency while evacuating a building.


G4O1 applies to a building constructed in an alpine area.


Protection while evacuating

G4O1 specifies that occupants of buildings in alpine areas must be protected while evacuating in an emergency. The protection measures are only required to assist while the building is being evacuated. The additional measures included in Part G4 are necessary because of the conditions which can exist in alpine areas.

Precedence over other BCA provisions

G4O1’s Application provision clarifies that if there is any contradiction between the requirements in this Part and the rest of the BCA, then the provisions of Part G4 will take precedence.

Functional Statements

A building in an alpine area is to be provided with additional measures in view of the increased difficulties in fire-fighting and maintaining access and means of egress in snow conditions.


G4F1 only applies to a building constructed in an alpine area.

Additional safety measures necessary

G4F1 adds an additional dimension to G4O1 by indicating that additional measures are necessary because of the difficulties faced by fire brigades in gaining quick access to buildings during an emergency and maintaining building access and egress during snow conditions.

Precedence over other BCA provisions

The application provision included as part of G4F1 clarifies that if there is any uncertainty between the requirements in this Part and the rest of the BCA, then the provisions of Part G4 will take precedence.

Performance Requirements

An external doorway from a building in an alpine area must be installed so that opening the door is not obstructed by snow or ice.


G4P1 applies to a building constructed in an alpine area and overrules other Performance Requirements of NCC Volume One.


External doors must continue to operate

G4P1 requires external doors to continue to operate effectively in snow conditions so people can leave in an emergency by the normal egress route (i.e. the doorway).
Such a doorway must not be made inoperable by deposits of snow and ice. Care needs to be taken to avoid locating doorways where:

  • snow falling from adjoining roof areas could affect egress paths; and
  • re-entrant corners of a building increase the potential for snow to be trapped.

Precedence over other BCA provisions

G4P1’s Application provision clarifies that if there is any uncertainty between the requirements of G4P1 and the rest of the BCA, then G4P1 will take precedence.

A building in an alpine area containing external trafficable structures forming part of the means of egress must be constructed so that those structures remain, as far as practicable, useable under snow conditions.


G4P2 applies to a building constructed in an alpine area and overrules other Performance Requirements of NCC Volume One.


External trafficable structures must be usable

Any external structures used as part of an egress route must remain accessible in snow conditions. An external balcony not designed for egress from the building would not need to comply.

To comply with this provision it is necessary to make sure that snow build up is avoided and that the surfaces reduce the potential for people slipping.

Precedence over other BCA provisions

G4P2’s Application provision clarifies that if there is any uncertainty between the requirements of G4P2 and the rest of the BCA, then G4P2 will take precedence.

A building in an alpine area must be constructed so that snow or ice is not shed from the building onto the allotment, any adjoining allotment, road or public space in a location or manner that will—

  1. obstruct a means of egress from any building to a road or open space; or
  2. otherwise endanger people.


G4P3 applies to a building constructed in an alpine area and overrules other Performance Requirements of NCC Volume One.


Adjacent areas — snow or falling ice

Areas adjacent to the building should not be subjected to heavy deposits of built-up snow or falling ice which could harm:

  • people evacuating (i.e. roofs must be designed to avoid depositing snow on egress routes from the building); and
  • people using the area adjacent to the building (i.e. snow from the roof area should not cascade on to public thoroughfares and roads or on to adjoining property in a dangerous manner).

Precedence over other BCA provisions

G4P3’s Application provision clarifies that if there is any uncertainty between the requirements of G4P3 and the rest of the BCA, then G4P3 will take precedence.

A building in an alpine area must have a fire safety system installed to—

  1. facilitate fire-fighting operations; and
  2. alert occupants in the event of an emergency.


G4P4 applies to a building constructed in an alpine area and overrules other Performance Requirements of NCC Volume One.


Installation of fire safety equipment

G4P4(a) requires that a building have equipment to facilitate firefighting operations. With the increased risk of fire development and access problems for fire brigades in alpine areas, it is important that suppression equipment be available to combat a fire in its early stages of development, to possibly prevent the fire reaching an uncontrollable stage.

It is not intended that occupants fight a fire if there is any danger to them. It is essential that occupants be able to evacuate safely before untenable conditions are reached.

Care will need to be taken in design and construction to ensure that water in fire-suppression equipment will not freeze, making the equipment useless.

G4P4(b) requires the installation of a system to alert occupants of an emergency. Where an external alarm is installed, care must be taken that the sub-zero temperatures do not freeze its mechanism.

Precedence over other BCA provisions

G4P4’s Application provision clarifies that if there is any uncertainty between the requirements of G4P4 and the rest of the BCA, then G4P4 will take precedence.

Deemed-to-Satisfy Provisions

(1) Where a Deemed-to-Satisfy Solution is proposed, Performance Requirements G4P1 to G4P4 are satisfied by complying with—

  1. G4D2 to G4D8; and
  2. for a building containing an occupiable outdoor area, Part G6.

(2) Where a Performance Solution is proposed, the relevant Performance Requirements must be determined in accordance with A2G2(3) and A2G4(3) as applicable.

The requirements of G4P1 to G4P4 will be satisfied if compliance is achieved with G4D2 to G4D8 in the case of buildings in alpine areas and for occupiable outdoor areas, Part G6.

(1) The Deemed-to-Satisfy Provisions of this Part apply to any building constructed in an alpine area in addition to other Deemed-to-Satisfy Provisions of NCC Volume One.

(2) Where any Deemed-to-Satisfy Provisions are in conflict, the provisions of this Part take precedence.

To clarify that Part G4 applies only to buildings in alpine areas, and its provisions override any others in the BCA which are in conflict.

Buildings in alpine areas only — G4D2(1)

G4D2(1) indicates that the requirements of Part G4 only apply to buildings constructed in an alpine area. See the definition of alpine area in Schedule 2.

Precedence over other provisions — G4D2(2)

G4D2(2) indicates that the provisions of Part G4 take precedence over any other provisions in the BCA, but only if they are in conflict.

External doors which may be subject to the build-up of snow must—

  1. open inwards or slide; and
  2. if inward opening, be marked “OPEN INWARDS” on the inside face of the door in letters not less than 75 mm high in a colour contrasting with that of the background; and
  3. be constructed so that the threshold is not less than 900 mm above the adjoining surface; and
  4. if it serves a corridor or stairway, be positioned in an alcove or recess with—
    1. no horizontal dimensions of the alcove or recess less than twice the width of the door; and
    2. the door positioned to open against a wall such that the distance from any part of its swing to the nearest point of entry of the stairway or corridor is not less than the width of the door.

To enable people to evacuate a building in an alpine area in an emergency without being impeded by snow and ice.

Doors in non-alpine areas

In most buildings, exit doors must open outwards to assist with evacuation. The outward opening door swings in the direction of people leaving the building. A door opening towards people leaving is considered to be potentially more dangerous because a “crush” may occur, where people pushing against the door prevents it from being opened.

Doors in alpine areas — G4D3(a)and (b)

In alpine conditions, the swing of outward opening doors may be impeded by snow and ice outside. Therefore, the door is allowed to open inwards provided adequate precautions are taken to enable the door to open towards the flow of people.

As external doors in most buildings open outwards, most people will not necessarily be expecting a door to open inwards. Accordingly, a readily-visible and understood sign must alert people to this feature.

Thresholds to required exit doorways — G4D3(c)

Every threshold to a required exit doorway must be located so that snow, etc will not prevent the door from opening. Accordingly, the threshold may need to be:

  • elevated to a point where it is above anticipated snow levels in that area of the building; or
  • protected by an awning or similar enclosure which prevents snow from obstructing the doorway.

Attention should be given to the geometry of the building where the threshold is located. The doorway should not be in a place where the roof will deposit large amounts of snow, or at re-entrant corners where snow drifts may form.

Doorways protected by alcoves or similar

Doorways protected from snow build-up by alcoves, etc are effectively exempt from G4D3, so long as they are clearly not subject to the build up of snow.

Alcoves — G4D3(d)

Where a doorway serves a corridor or stairway, an alcove or recess must be provided to protect against snow build-up. If a design indicates that such an alcove or recess will prevent snow build up, a builder, etc may be able to adopt the approach referenced above, and avoid the necessity for the door to open inwards. See Figure G4D3.

G4D3(d) does not apply where an external doorway opens directly from a room to the outside of the building.

Figure G4.3

Minimum dimensions of alcove or recess at external doorway

Minimum dimensions of alcove or recess at external doorway.

In a Class 2, 3, 5, 6, 7, 8 or 9 building or Class 4 part of a building, a system of emergency lighting must be installed in accordance with the Deemed-to-Satisfy Provisions of Part E4

  1. in every stairway (other than those within a sole-occupancy unit in a Class 2 or 3 building or Class 4 part of a building); and
  2. in every public corridor or the like leading to an exit; and
  3. externally above every doorway opening to a road or open space; and
  4. in any storey of the building if illumination sufficient for safe egress will not be available under conditions of emergency.

To enable people to evacuate a building in an alpine area in an emergency without being impeded by lack of light.

Emergency lighting in buildings in alpine areas

G4D4 requires emergency lighting in all Class 2–9 buildings in alpine areas. Expected delays in emergency personnel arriving on the scene, means emergency lighting is necessary to assist people evacuating.

Emergency lighting provides illumination for exit paths, etc during a power failure (which is a likely scenario in a fire). The lighting must be effective and installed to cover exit paths as nominated.

G4D4 and Part E4

The technical aspects of the installation of emergency lighting must be in accordance with Part E4. However, the location of emergency lights must comply with G4D4, irrespective of any location parameters specified in Part E4.

Lighting in stairways — G4D4(a)

G4D4(a) requires lighting to be provided to every stairway within a building, except within a sole-occupancy unit of a Class 2 or 3 building and the Class 4 part of a building. This is to make sure that common exit routes are still negotiable in an emergency.

Lighting in exit paths— G4D4(b)

G4D4(b) requires lighting in main exit paths. The key description is public corridors, public hallways or the like, inferring that any pathway used as a general or common exit route by occupants must be provided with emergency lighting.

Emergency lighting — G4D4(c)

G4D4(c) requires emergency lighting externally above every doorway opening to a road or open space. This enables occupants to negotiate any obstacles when evacuating in darkness.

G4D4(c) applies only to doorways leading directly or via the allotment land to a public road. Doorways opening on to enclosed courtyards or similar enclosed areas are not required to comply.

Emergency lighting and darkness — G4D4(d)

G4D4(d) is a performance criterion and will require assessment of the building layout to determine the need for emergency lighting in areas other than those specified in G4D4(a), (b) and (c). The aim of G4D4 is to assist people by providing illumination in pathsof travel while evacuating the building.

Where the designer or appropriate authority believes there are problems which may be created due to darkness, then emergency lighting must be installed.

Exit signs — Part E4

Note that while it is not referenced in Part G4, emergency exit signs need to be installed in accordance with Part E4.

External stairways, ramps, access bridges or other trafficable structures serving the building must—

  1. have a floor surface that consists of expanded mesh if it is used as a means of egress; and
  2. have any required barrier designed so that its sides are not less than 75% open; and
  3. for a stairway, have goings (G), risers (R) and slope relationship quantity (2R + G) in accordance with—
    1. Table D3D14; or
    2. Table G4D5; and
  4. for a ramp serving as an exit and not serving as an accessible ramp, have a gradient not steeper than 1:12; and
  5. where a ramp is also serving as an accessible ramp under Part D4, be in accordance with AS 1428.1.
Table G4D5 Alternate stair riser and going dimensions
Riser (R) Going (G) Slope relationship (2R + G)
Max Min Max Min Max Min
150 115 375 355 675 605
Table Notes

Dimensions are in mm.

To enable people to evacuate a building in an alpine area in an emergency without being impeded by steep ramps.

External ramps must not be too steep

G4D5 aims to ensure that egress is not impeded by steep ramps. The maximum slope of 1:12 is less than the 1:8 allowed in Part D3 because of the difficulty associated with negotiating ramps in snow and ice conditions. G4D5(a) acknowledges that if exit ramps are required for access by people with disabilities they must comply with AS 1428.1.

A building must be so constructed that—

  1. if any part of an external wall is more than 3.6 m above the natural ground level — the distance of that part from a boundary other than a road alignment is not less than 2.5 m plus an additional 100 mm for each 300 mm or part thereof by which that part of the wall exceeds a height of 3.6 m; and
  2. if an exit doorway discharges into a court between wings of a building and that area may be used for vehicle access to the building, the distance between wings must be not less than 4 m; and
  3. where an exit doorway discharges opposite a feature that could entrap snow or an embankment that is more than 900 mm above the threshold of the doorway, a distance of not less than 4 m must be provided between the doorway and the feature.

To enable people to evacuate and emergency services to access a building in an alpine area in an emergency without being impeded by snow build-up around the building.

Snow build-up between and around buildings

The design and construction of a building in an alpine area must not aid dangerous levels of snow build-up between and around buildings. This control:

  • assists with egress in an emergency;
  • helps vehicle access around the buildings, both for snow clearing and emergency situations; and
  • minimises the risk of snow or ice falling from the roof on to adjoining lots or egress routes.

G4D6(a) addresses the set-back distance for external walls from the boundary of adjoining allotments. The aim is to make sure that a reasonable distance is created between buildings to reduce the amount of snow build-up between properties. G4D6(a) applies only to the area adjacent to that part of the wall which is more than 3.6 metres in height.

G4D6(b) describes distances between wings of a building where the exit doorway discharges into this area. The external walls of a building should not create an alcove which traps snow, making evacuation difficult.

G4D6(c) deals with the problem of features adjacent to an exit doorway which could trap snow and complicate egress.

The term “barrier” is used to describe the feature which could entrap snow. Because the aim of G4D6(c) is to avoid the problems created by snow drifts, it would be reasonable to interpret “barrier” as including any feature which could hold the snow, including fences, cuttings to roadways, walls of adjacent buildings and the like. See Figure G4D6.

Figure G4D6

Discharge of External Doorways in alpine areas.

Discharge of External Doorways in alpine areas.

(1) Every Class 2, 3, 5, 6, 7, 8 or 9 building must have—

  1. a manually operated fire alarm system with call-points complying with AS 1670.1; and
  2. fire hydrants installed in accordance with E1D2(2); and
  3. fire hose reels installed in accordance with E1D3(2) to (7), except that in a Class 2 or 3 building—
    1. for the purpose of E1D3(2), a sole-occupancy unit is considered to be a fire compartment; and
    2. for the purpose of E1D3(3)(b), a sole-occupancy unit may be served by a single fire hose reel located at the level of egress from that sole-occupancy unit; and
    3. for the purpose of E1D3(6), a fire hose may pass through a doorway in bounding construction referred to in C4D12.

(2) The requirements of (1)(c) do not apply to a Class 8 electricity network substation.

To provide for the installation of adequate fire safety equipment suitable to the conditions experienced in alpine areas.

Fire alarm system — G4D7(1)(a)

G4D7(1)(a) requires a manually-operated, fire-alarm system. This system must be supplemented by call-points to notify the local fire authority. The activation mechanism of the manual call-point may also activate the alarm system. This will provide an additional audible warning to the automatic systems required by Part E2.

Where an external alarm is installed, sub-zero temperatures must not freeze its mechanism.

Hydrants — G4D7(1)(b)

G4D7(1)(b) requires that hydrants be installed in all the nominated buildings in accordance with E1D2(2). A fire hydrant must be operable in sub-zero conditions, and any water in the mains should not freeze.

Hose reels— G4D7(1)(c)

G4D7(1)(c) requires that hose reels be installed in all the nominated buildings in accordance with E1D3, except that E1D3(2), (3)(b) and (6) are modified for Class 2 and 3 buildings.

  • G4D7(1)(c)(i) — Fire hose reels are required to be installed, irrespective of whether fire hydrants are required, if fire compartments exceed 500 m2. For the purpose of a Class 2 or 3 building, a sole-occupancy unit is considered a fire compartment.
  • G4D7(1)(c)(ii) — Generally, fire hose reels are required to be installed on the storey they are to service. In the case of Class 2 or 3 buildings, a concession is provided when a sole-occupancy unit occupies more than one storey if the fire hose reel is located at the level egress from that sole-occupancy unit. There is no limitation on the size or number of storeys within the sole-occupancy unit served by the hose.
  • G4D7(1)(c)(iii) — Doors to sole-occupancy units of Class 2 or 3 buildings may remain open for the hose to pass through. To require a fire hose reel in each sole-occupancy unit could be impractical, therefore fire hose reels are allowed to be placed in a common area and then pass through the entrance door to the unit.

A fire hose reel must be operable in sub-zero conditions, and any water in the mains should not freeze.

Class 4 parts of buildings

G4D7 has not been applied to Class 4 parts of a building. It is extremely unlikely that any of the services and equipment required by G4D7 will be located within a sole-occupancy unit in any residential building. In, for example, Class 2 and Class 3 buildings it is most likely that such services and equipment will be located in common areas.

The requirement for the installation of fire-fighting services and equipment in the non-Class 4 parts of the building within which the Class 4 part is located, will provide for the safety of the occupants of the Class 4 part.

Electricity network substations

G4D7(2) provides an exemption to the requirements for fire hose reels for electricity network substations.

Every Class 2, 3 or 9 building must display a notice clearly marked “FIRE ORDERS” in suitable locations near the main entrance and on each storey, explaining—

  1. the method of operation of the fire alarm system and the location of all call-points; and
  2. the location and methods of operation of all fire-fighting equipment; and
  3. the location of all exits; and
  4. the procedure for evacuation of the building.

To enable occupants to evacuate a building in an alpine area in an emergency without being impeded by lack of knowledge of the fire safety system, egress routes or evacuation procedures.


In Class 2, Class 3 and Class 9 buildingsG4D8 requires that a notice containing fire orders be displayed. They are necessary because there is a high probability that, in alpine areas, the occupants may be residing overnight or for short periods only, and will be unfamiliar with their surroundings.

Fire escape information needs to be displayed prominently near the main entrance and on each storey so that people new to the building can identify escape features, etc. A suitable location would be near the primary stairway. Additional advice on locating these items can be obtained from the appropriate authority or local fire authority.

Information must be conveyed in a clear and simple manner, because of the varying degree of technical understanding of people reading this information.

Class 4 parts of buildings

Class 4 parts of buildings have not been included in the coverage of G4D8 because buildings will not typically be used for short term rental accommodation in alpine areas. Therefore, residents are likely to be aware of safety requirements.