BCA-05

Use of Fire Walls under BCA Part C2: Clause C2.7

AUST  The use of fire walls in a design can provide efficiencies however any misunderstanding on the function of a fire wall or an incorrect interpretation can compound compliance issues with the Building code of Australia.

/ WHAT CAN FIRE WALLS BE USED FOR:

  • Create separate fire compartments so that fire compartment configurations for area and volume will comply relative to the required type of construction for the building
  • Create separate buildings
  • To separate different types of construction in a building
  • In class 9a and 9c buildings, fire walls separate patient care areas
  • Fire walls are a prerequisite for the use of horizontal exits
  • To separate sprinklered and un -sprinklered areas of a building

The following is a brief explanation on the correct use of a fire wall.

/ BUILDING CODE OF AUSTRALIA
The use of a fire wall requires considering a number of clauses in the Building Code of Australia. The definitions for a “fire wall” and “fire compartment” are key considerations that require careful application into a design.

/ PART A1: INTERPRETATION
A1.1 Definitions
Fire wall means a wall with an appropriate resistance to the spread of fire that divides a storey or building into “fire compartments”. Fire compartment means:

(a) the total space of a building; or
(b) when referred to in:

(i) the Objective, Functional Statement or Performance Requirements – any part of a building separated from the remainder  by barriers to fire such as walls and / or floors having an appropriate resistance to the spread of fire with any openings adequately protected; or

(ii) the Deemed-to-Satisfy Provisions – any part of a building separated from the remainder by walls and/or floors each having an FRL not less than that required for a fire wall for that type of construction and where all openings in the separating construction are protected in accordance with the Deemed-to-Satisfy Provisions of the relevant Part.

In noting the definitions above, the Building Code of Australia extracts below need to be interpreted and carefully applied to the particular design intent.

/ PART C2: COMPARTMENTATION AND SEPARATION
C2.7 Separation by fire walls

(a) Construction – A fire wall must be constructed in accordance with the following:

(i) The fire wall has the relevant FRL prescribed by Specification C1.1 for each of the adjoining parts, and if these are different, the greater FRL, except where Tables 3.9, 4.2 and 5.2 of Specification C1.1 permit a lower FRL on the carpark side.

(ii) Any openings in a fire wall must not reduce the FRL required by Specification C1.1 for the fire wall, except where permitted by the Deemed-to-Satisfy Provisions of Part C3.

(iii) Building elements, other than roof battens with dimensions of 75 mm x 50mm or less or sarking-type material, must not pass through or cross the fire wall unless the required fire resisting performance of the fire wall is maintained.

(b) Separation of buildings — A part of a building separated from the remainder of the building by a fire wall may be treated as a separate building for the purposes of the Deemed-to-Satisfy Provisions of Sections C, D and E if it is constructed in accordance with (a) and the following:

(i) The fire wall extends through all storeys and spaces in the nature of storeys that are common to that part and any adjoining part of the building.

(ii) The fire wall is carried through to the underside of the roof covering.

(iii) Where the roof of one of the adjoining parts is lower than the roof of the other part, the fire wall extends to the underside of:

(A) the covering of the higher roof, or not less than 6 m above the covering of the lower roof; or
(B) the lower roof if it has an FRL not less than that of the fire wall and no openings closer than 3 m to any wall above the lower roof; or
(C) the lower roof if its covering is non- combustible and the lower part has a sprinkler system complying with Specification E1.5.

(c) Separation of fire compartments — A part of a building separated from the remainder of the building by a fire wall may be treated as a separate fire compartment if it is constructed in accordance with (a) and the fire wall extends to the underside of:

(i) a floor having an FRL required for a fire wall; or

(ii) the roof covering.

C2.8 Separation of classifications in the same storey.

If a building has parts of different classifications located alongside one another in the same storey
(b) the parts must be separated in that storey by a fire wall having:

(i) the higher FRL prescribed in Table 3 or 4; or

(ii) the FRL prescribed in Table 5.

/ FACTORS TO NOTE
A fire wall is not simply any wall having a fire-resistance level (FRL). The purpose and function of the wall must be clear as there is a difference between a “fire wall” and a ‘fire-rated internal wall’ in the Building Code of Australia (BCA). This difference is the purpose and function of the wall. The essential difference between a ‘fire wall’ and an internal fire rated wall is to be found in the higher FRLs sometimes laid down for the former pursuant to the building’s type of construction and the higher requirements specified for protection of any openings either side and through a fire wall. The use of a fire wall to create separate buildings requires very careful thought particularly in relation to building services, ownership, titles, exits and egress, access to fire services and the separation of openings.

The interconnection and use of common services for separate buildings may not be permitted. For example the division of a class 2 building by a fire wall simply to negate providing a fire hydrant when the total floor area exceeds 500m² may not be the correct decision and use of fire walls when all other factors are considered.

In respect to openings, clause C3.3 of the BCA “Separation of external walls and associated openings in different fire compartments” requires the distance between parts of external walls and any openings within them in different fire compartments separated by a fire wall must not be less than that set out in Table C3.3, unless:

(a) those parts of each wall have an FRL not less than 60/60/60; and
(b) any openings protected in accordance with C3.4.

The distances required between openings is a factor of the angle of exposure between the openings. For example, opposite openings must be 6m apart whilst openings at an angle of more than 135 degrees to less than 180 degrees need a 2m separation distance.

The sketch below provides an example of this requirement.

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