Preventing the spread of fire to Class 1a buildings

Occupant life safety is the primary goal of Australian building codes. However, the NCC’s fire separation requirements are often misunderstood. The risk of fire spread demands adequate separation or protection of Class 1a dwellings from fire sources. These are commonly another unrelated building on an allotment, or the allotment boundary. There are several ways this separation can be achieved. Here are 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 requires 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), a 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 located between or attached to a dwelling 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 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 (see Figure 3).

Buildings on the same allotment

The allotment in Figure 4 is not subdivided. Therefore, the external walls of the Class 1a buildings are not required to have protection under 9.2.1(b). This applies to dwellings not within 1800mm. 9.2.7(e) allows the use of a separating wall to the Class 10a to provide protection in this scenario.

What if subdivision is intended?

As explained above, boundary distance changes your obligations and how they need to be met.  Separation of more than 900mm can afford flexibility and the option for an allotment to be subdivided in future.

As demonstrated in Figure 5, when subdivision occurs after occupation a performance solution to achieve the NCC Performance Requirements may be needed. The external upper storey wall of the Class 1a (within 900mm of a future allotment boundary) does not commence above a separating wall or commence at a slab or footing. Solutions to consider include the horizontal projection requirements under clause 9.3.4 of the HPS. You must address the risks and implications for beams which support the upper storey wall in the event of a fire. You also need to consider if the wall at the boundary was a separating wall and assess its ability to provide protection from both sides.

To find out more, contact HIA's Contracts and Compliance team

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