Walls

Guiding principles

Walls are vulnerable to the ignition of external cladding and the ignition of combustible framing and insulation within the wall cavity. Walls can ignite through direct contact with the fire front or from the burning of debris that have built up against or within the wall cavity. When retrofitting, efforts should be made to ensure the wall system is resistant to the inevitable build up of debris.

Walls are also vulnerable to consequential fires. When flames and embers (and radiant heat) reach the house, they can penetrate damaged or dislodged cladding, allowing fire to spread into the wall cavity. Once the wall cavity is burning it is very likely that flames will progress into the roof cavity and into the living areas of the house. Your primary objective for retrofitting wall systems, should be to maintain the integrity of the building’s envelope, by sealing gaps, repairing damage, and replacing combustible materials with non-combustible alternatives.

How to prevent wall cladding ignitions

It is possible to replace combustible cladding with a non-combustible alternative, although in some cases this can be expensive. For situation where where fire exposure is BAL 12.5 or less and funds are a limiting factor consider non-combustible cladding for at least the first 500mm above any horizontal projections where debris can accumulate. Also identify all the combustible elements (wood heaps, cars, shed) around the house that could fuel a consequential fire against the wall. Remove or relocate these hazards or consider installing a barrier between the house and the hazard (see Screen plantings).

How to prevent ignitions within wall cavity

It is common for gaps and cracks to form in the wall cladding over the lifespan of the building. These gaps and cracks  should be sealed as a matter of urgency – when left unrepaired, gaps in the walls surface will provide a point of entry for embers and surface fire which may ignite surrounding materials leading to more extensive damage and the possible destruction of the house. These cavity fires can be difficult to monitor and suppress.

Retrofitting for bushfire protection

The following table contains information on retrofitting a wall system. These measures will provide some protection against most bushfire hazards, however they may not protect against direct flame contact from burning vegetation or consequential fires. If you have identified a source of Consequential fire, consider removing or relocating the source or installing a barrier between the house and the source (see Screen plantings).

The risk of a consequential fire (e.g., the risk of fire spreading from a neighbouring house) is often not economically viable to mitigate. For example, mitigating this risk completely may require drastic changes in building materials and design. As such, it is important to acknowledge the risk of a consequential fire, and include it as a factor in your bushfire survival plan. It is also important to note that even the most well built home is vulnerable to bushfire if there is a weakness or flaw in the buildings design or maintenance. No home is guaranteed to be 100% bushfire safe.

It is common to gaps to form between adjacent buildings systems, such as between windows and the surrounding cladding – although small, this gap is vulnerable to ember and flame entry