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Firewalls

Fire safety is a critical aspect in multi-residential construction. Walls that separate residences are the major element in multi-residential construction relating to fire safety. Recent changes to the Standard Building Regulation (1993) have seen fire safety included as a major aspect that must be checked at the Final Inspection Stage for a Class 1a Building. Incorrect construction or lack of consideration given to separating wall systems can expose building contractors to excessive rectification bills. Even worse, loss of property or life, due to a fire spreading between residences can have serious legal implications for building contractors.

The Building Code of Australia Defines a Class 1a Building as

  • A detached house or
  • One or more attached dwellings, each being a building separated by a fire-resistant wall, including row houses, terrace houses, town houses or villa units. Duplexes and town houses are the most common form of attached dwellings in residential construction that require fire separation between adjoining residences.

Fire separation must achieve compliance with the Performance Requirement of the BCA (compliance with BCA p2.3.1 and be deemed to satisfy BCA P3.7.1.8). The former provision requires that Class 1a Buildings be protected from the spread of fire from adjacent buildings and the allotment boundary other than a boundary adjoining a road or public space. The latter deemed to satisfy provision states that fire separating walls Between Class 1 dwellings must have a continuous fire resistant level (FRL) of not less than 60/60/60 (a grading rate in minutes for structural adequacy/integrity/insulation) and commence at the footings extending to the underside of a non-combustible roof covering across voids in roof spaces between residences and over eaves and verandahs.

This separating wall must not be crossed by timber or any other combustible building elements except for roof battens with dimensions of 75X50mm. Any gaps between the top of the wall and the underside of the roof covering should be packed with mineral fibre or other suitable fire resistant material as recommended by the manufacturer. In the case of combustible roof covers, the fire separating wall should extend 450mm above the combustible material.

Fire Separation Walls

  • Should extend completely to the underside of the roof
  • Mineral fibre should be in place between the wall and to the underside of the roof sheeting
  • Should be fully sealed to the roof with no penetrations
  • Should have no timber penetrations except for roof battens greater than 75X50mm
  • There should be no gap greater than 50mm between the wall and underside of the roof which should be packed with mineral fibre

A Fire Separation Wall is a wall with appropriate resistance to spread of fire that divides a storey or building into a fire compartment

Ceilings Should be Constructed

  • as per the CSR Gyprock Fire and Acoustic Design Guide
  • Of 2 layers of 16mm Gyprock Fyrcheck plasterboard... or
  • Perforated gypsum lath with a normal paper finish... or
  • 12mm fibrous plaster reinforced with 13mm X 13mm X 0.7 galvanised steel wire mesh located not more than 6mm from the exposed face... or
  • Fibre-cement sheeting... or
  • Pre-finished metal sheeting not exceeding 1mm thick... or
  • 12mm cellulose cement flat sheeting

External Walls and Soffits

  • External walls should extend to the underside of the soffit and preferably to the outside by more than 900mm
  • External walls including gables are required to be of masonry-veneer or masonry construction 90mm thick
  • Soffits should have a non-combustible eaves lining
  • Where the external wall does not extend to the underside of the roof, mineral fibre should be included

Building Between Units

  • The garage between the units should be single, walled to the height of the roof space and of non- combustible material
  • The carport between buildings should be more than 2/3 enclosed

Roof Lights Must be

  • non-combustible
  • an aggregate area not more than 20% of roof or part of the roof
  • not less than 900mm from the allotment boundary other than the boundary adjoining a road or other public space
  • 1.800mm apart from any roof light or another building or detached part of the same building

Carports and Boundary Clearances

  • Units should be correctly separated from carports
  • Boundary clearances should be greater than 900mm

Major Issues Involving Fire Separation

  • Binders for trusses being carried through fire separating walls
  • Numerous penetrations being made through separating walls that break down the fire rating
  • Separating walls not being carried through to the underside of the roof sheeting and packed with an appropriate fire resistant material to manufacturer's specifications
  • Gaps not being packed between separating walls and external wall construction
  • Inadequate protection to roof spaces of eaves, verandahs and voids that are common to more than one unit/dwelling

Reason for Firewall Failure

  • Approved plans and specifications which do not provide details of every construction application related to fire separating wall systems
  • Builders not adhering to proper fire separating wall installation requirements
  • Building supervisors not providing adequate information and supervision to installers of fire separating wall systems
  • Installers or trade contractors not possessing an adequate understanding of how to construct a continuous fire separating wall system

Corrective Measures

Proper construction of separating walls starts at the footings and slab. Engineer's details should be closely followed to ensure sufficient support for separating walls, in particular masonry walls. The detail of finishing the top of the wall to the underside of roof coverings is an important aspect and must be complete to fine tolerances.

Close consideration must also be given to construction of separating walls in relation to verandah and eaves overhangs. Another area to be closely checked is the vertical gap between the end of the separating wall and the inner face of external brickwork.

All trades involved in work related to separating walls e.g. electricians and plumbers should be advised that penetrations or chasing into separating walls is not permitted for Class 1a Buildings.

To Ensure Firewalls are Properly Constructed

  • Details on approved plans for construction should be closely followed
  • Proper materials should be employed
  • The designer and building certifier should be closely consulted;
  • All trades involved with work on separating walls should be informed and supervised
  • Inspections should be conducted by a building certifier responsible for approving the building work

Builders should maintain full documentation on fire separating wall design details, manufacturer's recommendations, installation compliance certificates (where applicable) and ensure that they can satisfy compliance with building certifier's requirements.