Preventing the spread of fire to Class 1a buildings

There are several ways this separation can be achieved, In the below scenarios we unpack a few basic principles to ensure an appropriate level of protection is delivered and the role of different clauses is understood.

Controlling fire spread

The NCC Performance Requirement H3P1 intends to ensure life safety by avoiding the spread of fire to Class 1a buildings. The Deemed-to-Satisfy provisions require separation of buildings or fire protection. This ensures the distance between them and the materials is suitable.

A fire threat could come from:

• another building other than an associated Class 10 building
• the allotment boundary, other than a boundary adjoining a road or public space.

To correctly apply the provisions, you need to establish the building in question is on the same or a different allotment. This will require the application of one or more Housing Provisions Standard (HPS) clauses:

• 9.2.1 External walls
• 9.2.3 Construction of external walls
• 9.2.4 Class 10a buildings
• 9.2.5 Protection of Class 1 buildings – Class 10a between Class 1 and the allotment boundary
• 9.2.6 Protection of Class 1 buildings – Class 10a between Class 1 and other buildings on allotment
• 9.2.7 Protection of Class 1 buildings – Separation of Class 10a buildings on an allotment
• 9.3.1 Separating walls

Triggers for protection

Method 1: Adequate separation — Buildings on different allotments  

With increased distance, there is a reduction in radiant heat another building will be exposed to. A wall not within 900mm of allotment boundary doesn’t require protection under 9.2.1 of the ABCB Housing Provisions Standard (HPS).

Method 2: Fire walls and separating walls

Where the external wall of the Class 1 building is within 900mm of a boundary or within 1800mm from another building on the same allotment (that is not associated with the building), the wall is required to:

• have an FRL of not less than 60/60/60 when tested from the outside; or
• be of masonry-veneer construction in which the external masonry veneer is not less than 90 mm thick; or
• be of masonry construction not less than 90 mm thick.

Class 10a

While a Class 1a does not require protection from an associated private garage or in its own right, fire protection can be provided to a Class 1a building via a Class 10a building located between a dwelling (including where attached) and a boundary or fire source. This is required where it would otherwise reduce the degree of protection from a fire source offered by distance.

It is common for a Class 10a building wall to provide protection for the Class 1a building to prevent the spread of fire from an allotment boundary. Configurations under clause 9.2.5 of the HPS detail those allowed.

Where a Class 10a building is not sited directly and wholly between the allotment boundary and the Class 1a building, the potential of fire spreading from the allotment boundary to the Class 1a still exists. Therefore, fire separation would be required.

How does subdivision affect fire separation obligations?

In a proposed development where Class 10a's are located between another building and below a Class 1a dwelling such as in the configuration below, the choice to subdivide could have implications for fire separation solutions.

Buildings on different allotments

Providing >900 mm separation from the boundary on allotments which are subdivided to Class 1a dwellings would meet 9.2.1(a). An attached Class 10a sited directly between the Class 1a would lower the protection offered by distance. In this case protection can be provided by a separating wall between the non-appurtenant Class 10a buildings akin to 9.2.5(b) (see Figure 4).

Buildings on the same allotment

Figure 5, shows the same configuration on an allotment that is not subdivided. For dwellings not within 1800mm of another building (of any class) on the same allotment, the external walls of the Class 1a buildings are not required to have protection under 9.2.1(b).

Note the associated Class 10a’s are within 900mm of a different building, but 9.2.7(e) allows the use of a separating wall to the Class 10a to provide protection to the Class 1 in this scenario.

9.2.1 (b) requires where the distance between the buildings is less than 1800mm protection is required. This is measured at right angles from the higher building to the vertical projection of the lower separating wall in accordance with 9.2.2(d) and would include any upper storey wall. The external wall requiring protection must commence either above a separating wall, or from the footing or ground floor slab in accordance with 9.2.3 of the HPS.

What if the choice to subdivide changes?

As explained above, separation distance changes your obligations and the options for how they are met. Subdivision provides for reduced separation distances and more flexibility in design.

Where subdivision did occur, fewer elements could be subject to fire-protection under the same arrangement compared to if the subdivision did not– despite the fire source being the same. 

Where subdivision did not eventuate, a Performance Solution to achieve the NCC Performance Requirements may be achievable where the external upper storey wall of the Class 1a requires protection under 9.2.1(b). Solutions may involve demonstrating compliance with H3V1. 

Alternatively, where fire protection is provided by a wall that did not propose to commence above a separating wall, or commence at a ground floor slab or footing, a Performance Solution could be proposed for the consideration of the relevant authority that addressed:

• the horizontal projection requirements under clause 9.3.4 of the HPS, 
• the risks and implications for beams which support the upper storey wall in the event of a fire.

To find out more, contact HIA Building and Planning Services.

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