Construction in Bushfire Zones

The Bushfire Attack Level determines the construction requirements for new buildings and alterations / additions. We will look at these in more detail to give an overview of what to expect during the planning stages. There are also minimal protection measures that should be taken out regardless of the Bushfire Attack Level. The earlier these can be considered in the design phases the less impact they will have on the design and cost outcome.

Minimal Protection Measures

These are easy inclusions that should be made in any building. Most of the minimal protection measures you can undertake are in response to ember attack, which results in 85% of houses lost from bushfire. Ember attack can occur over distances greater than 100 metres from the bush firefront. Any gaps, cracks or areas where embers and fuel can lodge (leaves, twigs, debris) significantly reduces a building’s resistance to bush fire attack.

• General

  Seal all gaps (>3mm) around the house (excluding subfloor) with; appropriate joining strips, flexible silicon based sealant, or mesh with a maximum aperture of 2mm, made from corrosion resistant steel, bronze or aluminium.

• Subfloor

  Removal of combustible materials and keeping areas clear and accessible.

• External Walls

  Install sarking with a flammability index of not more than 5 behind weatherboards or other external cladding when they are being replaced for maintenance or other reasons.

• External Windows

  Install mesh with a maximum apertureof 2mm, made from corrosion resistant steel, bronze or aluminium to all external doors and openable windows

• External Doors

  Install weather strips, draught excluders or draught seals at the base of side-hung doors.

• Roofs

  Seal around roofing and roofpenetrations with a non-combustible material.

  Install sarking with a flammability index of not more than 5 beneath roofing.

  If installed, gutter and valley leaf guards should be non-combustible.

• Vents & Weepholes

  Seal vents and weepholes in external walls with mesh (with an aperture size of 2 mm) of corrosion resistant steel, bronze or aluminium.

BAL Construction Requirements

These protection measures are required by AS3959 - Construction of Buildings in Bushfire-Prone Areas and increase in response to each BAL rating. The following table outlines these requirements;

RESOURCES

AS3959 - Construction of Buildings in Bushfire-Prone Areas

The Australian standard, a copy is available for purchase.

NSW RFS Building Best Practice Guide

A guide to upgrade existing buildings to increase resilience from bush fire attack.