Fire-separating walls in Class 1 buildings

What is a fire-separating wall?

Fire-separating walls (or party walls) are defined under Part 3.7.3 of the NCC as:

• a wall that separates Class 1 dwellings, or
• separating a Class 1 building from a Class 10a building which is not appurtenant to that Class 1 building.

These fire-separating walls must have a Fire Resistance Level (FRL) of not less than 60/60/60 or be of masonry construction of not less than 90 mm thick that:

• commences from the footings or ground slabs, and
• extends:
• to the underside of a non-combustible roof covering, or
• if the building has a combustible roof covering, then the separating wall must extend to not less than 450mm above the roof covering.

Designing a fire-separating wall

A separating wall that extends to the underside of a non-combustible roof covering must not be crossed by timber or other combustible building elements, except for roof battens with dimensions of 75 x 50mm or less, or roof sarking. Any gap between the top of the wall and the underside of the roof covering must be packed with mineral fibre or other suitable fire-resisting material.

Where a building has a masonry veneer external wall, any gap between the separating wall and the external masonry veneer must be:

• not more than 50mm, and
• packed with mineral fibre or other suitable fire-resistant material with the packing arranged to maintain any weatherproofing requirements (details contained in Part 3.3.4 of the NCC, Volume 2).

Eaves, verandahs and similar spaces that are open to the roof space and are common to more than one Class 1 dwelling must be separated by a non-combustible lining. Any service openings in a masonry separating wall must have an FRL of not less than -/60/60.

More details are provided in Clause 3.7.3.3  in relation to electrical wires and cables penetrating a separating wall, including electrical switches, outlets, sockets or the like in a separating wall.

FRL or Fire-Resistance Level is denoted with three figures – for example, in FRL 60/60/60, the first figure denotes a ‘structural adequacy’ period of 60 minutes; the second figure denotes an ‘integrity’ period of 60 minutes; and the third figure denotes an ‘insulation’ period of 60 minutes. A dash indicates that there is no requirement for that criterion such as -/60/- where the criterion is 60 minutes for integrity only. 

To find out more, contact HIA’s Building Services team.

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