BAL Ratings Explained
Bushfire Attack Level Ratings Explained

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Bushfire Attack Level (BAL) ratings dictate both the construction methods and materials used in bushfire prone areas. The purpose of BAL ratings is to help prevent bushfires from destroying buildings and spreading to other areas. Each BAL rating is assumed to carry the same risks as the previous rating, as well as additional risks.

When it comes to insulation for BAL rated buildings, it is important to consider into the design products that are ‘fit for purpose’.

To adhere to this consideration, Knauf Insulation recommends the use of non-combustible products that are tested and pass the requirements of AS 1530.1. Although not required by AS 3959 - Construction of Buildings in Bushfire Prone Areas (the Standard), non-combustible insulation will provide increased protection against ember attack.

The Standard mainly relies on sarking with a low flammability index to protect against ember attack however, sarking can be damaged (rips, holes etc.) during construction or operational phase of its lifetime. The damage can lead to a void in your ember defence system.

Non-combustible insulation is an extremely effective building material to protect against ember attack. Non-combustible insulation is inert to fire and has a very tight meshing of fibres, this means if embers land on the insulation they simply burn out without melting or disrupting the material. Under sustained ember attack, it is possible for some sarking materials that are made from polypropylene, paper or other plastic materials to become damaged and potentially cease to function.    

The main considerations regarding insulation for BAL ratings as per AS 3959 are:

  • Exposed external wall components comprise of non-combustible materials
  • Roof covering to be a non-combustible material, and fully sarked, and;
  • have any gaps that are greater than 3mm filled with non-combustible material.

All of Knauf Insulation’s glasswool products are tested and successfully deemed non-combustible to the requirements of AS 1530.1 and the table below summarises all of the different BAL zones and the recommended insulation product for each application.

  Knauf Insulation recommended products
BAL RatingDescriptionRoof (directly under roof lining)Wall (external wall)Ceiling (on ceiling lining)
BAL 12.5 - 40The main performance criteria for BAL 12.5 - BAL 40 is mitigating the risk of spread of flame, which is predominantly generated through airborne embers. Knauf Insulation recommends the use of non-combustible insulation products for use in BAL zones 12.5 - 40.Knauf Insulation Space Blanket® R1.3 x 55mmEarthwool® Wall insulation R2.0 – R2.7SHDEarthwool® Ceiling insulation R4.0-R6.0
BAL FZBAL FZ zones are very high risk and require specific fire rated level (FRL) systems be constructed. These systems require sign off from fire engineers and building certifiers prior to construction.Knauf Insulation Space Blanket® R1.8 is commonly used as a component of BAL FZ systems x 75mmEarthwool® SoundShield R2.5HD and R2.7SHD are commonly used as a component of BAL FZ systemsEarthwool® Ceiling insulation R4.0 – R6.0 are commonly used as a component of BAL FZ systems

Please note: the building certifier should approve all products suggested by Knauf Insulation in the above table prior to purchase and/or installation to ensure the products are fit for purpose and that they will contribute to the required performance (insulation alone will not achieve all the requirements of AS 3959).

Additional details on BAL ratings are available on the New South Wales Rural Fire Service website.

Knauf Insulation Recommended Products

Space Blanket®


Earthwool® Wall batt

Earthwool® Ceiling batt