Bushfire safety and windows

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Bushfire safety

Devastating bushfires are unfortunately an all too common occurrence across Australia. In response to recent bushfire attacks new building regulations have been introduced to give occupants increased protection until a fire front passes. The new Standard details various construction methods and materials that must be used depending on your home’s level of bushfire risk.

New homes, as well as renovations including garages, carports and verandas that share a common roof with the house, must comply with these new rules. The requirements include changes to the materials used for floors, walls, doors, roofs and windows. The added benefit in using windows that provide good fire safety is that they will often provide increased energy efficient performance as well.

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Bushfire Attack Level

Under the revised building Standard, all new homes and renovations are to be assessed and rated to one of six Bushfire Attack Level (BAL) categories ranging from low to extreme. The BAL levels are based on heat flux exposure thresholds, which measure the amount of energy per square metre of radiant heat exposure. Once the BAL has been determined, specific construction requirements must be followed, ranging from ember protection to direct flame protection.

Your Bushfire Attack Level can be assessed by an architect, building designer, building surveyor or builder. Alternatively, you can assess your property’s BAL rating yourself. Information on BAL assessments is contained within the Australian Standard AS 3959 – 2009 Construction of Buildings in Bushfire Prone Areas.

Once the assessment is completed it will need to be provided to the relevant building surveyor for confirmation. The relevant construction methods of your home’s BAL rating will then need to be included in the design documents lodged for a building permit.

 

The six bushfire attack levels and their predicted risk levels

Bushfire Attack Level (BAL) Description of predicted bushfire attack and levels of exposure Risk
BAL-Low There is insufficient risk to warrant specific construction requirements Very low
BAL-12.5 Ember attack Low
BAL-19 Increasing levels of ember attack and burning debris ignite by windborne embers together with radiant heat exposure of between 12.5 and 19kW/m2 Moderate
BAL-29 Increasing levels of ember attack and burning debris ignited by windborne embers, together with radiant heat exposure of between 19 and 29 kW/m2 High
BAL-40 Increasing levels of ember attack and burning debris ignited by windborne embers together with increasing radiant heat exposure of between 29 and 40 kW/m2, with the increased likelihood of exposure to flames Very high
BAL-FZ (flame zone) Direct exposure to flames from fire front in addition to radiant heat exposure of greater than 40 kW/m2 and ember attack Extreme

 

How this affects windows

Windows are often considered one of the weaker elements of a building. The revised building standard details changes to glazing requirements if your home is located in a Bushfire Attack Level category greater than BAL-Low. The information provided below is a condensed summary of the requirements for windows in bushfire prone areas. For more information on bushfire construction requirements contact your builder or local council.

Bushfire Attack Level (BAL) Window and glazing requirements
BAL-Low Standard window and door products may be used at this level. There are no special requirements.
BAL-12.5 Option 1 

Standard windows completely protected by bushfire shutters

Option 2

Standard windows completely protected by external metal mesh screens

Option 3

All openings must be screened internally or externally with metal screens
Exposed external window hardware to be made from metal
Minimum 4mm Grade A safety glass or glass blocks for all glazing within 400mm of ground
Window frames less than 400mm from the ground or other structure to be made from bushfire-resisting timber, timber with a density of 650kg/m3 or greater, metal or metal-reinforced uPVC.
BAL-19 Option 1 

Standard windows completely protected by bushfire shutters

Option 2

Standard windows completely protected by external metal mesh screens

Option 3

Where annealed glass is used it must be screened externally with metal screens
If 5mm toughened glass is used it must be screened internally or externally with metal screens
Exposed external window hardware to be made from metal
Minimum 5mm toughened safety glass or glass blocks for all glazing within 400mm of ground
Window frames to be made from bushfire-resisting timber, timber with a density of 650kg/m3 or greater, metal or metal-reinforced uPVC
BAL-29 Option 1 

Standard windows completely protected by bushfire shutters

Option 2

Minimum 5mm toughened safety glass used for all windows
Window frames to be made from bushfire resistant timber, metal or metal-reinforced uPVC
Exposed external window hardware to be made from metal
All glass within 400m of the ground or other structure to be screened externally with metal screens
All other openings to be screened internally or externally with metal screens
BAL-40 Option 1 

Standard windows completely protected by bushfire shutters

Option 2

Window frames and hardware to be made from metal
Minimum 5mm toughened glass used for all windows
Openable and fixed windows to be screened externally with metal screens
Hardware that supports the sash in its functioning of opening and closing must be made of metal
Seals to be made from silicone or material with a flammability index no greater than 5
BAL-FZ Option 1 

Standard windows completely protected by bushfire shutters

Option 2

Openable and fixed windows to be screened and either the window system has a Fire Resistance Level of at least 30 minutes or it has been tested to comply with Australian Standard AS 1530.8.2
Please note, the summary provided herein is for quick reference purposes only and does not contain the full requirements as described in the Standard. Please refer directly to the standard for full requirements.
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