Bushfire & BAL

How a property gets its BAL, and why in NSW that method is free to read

Applies in NSW the assessment method; the construction requirements that follow are national

We have reported that AS 3959 costs $286.63 to read, and that every compliance claim on a bushfire shutter points at it. That is true of the construction requirements. It is not true of the step before them. In NSW the method that decides which BAL a property gets is set out in a document the Rural Fire Service publishes free, and it says so in terms: it This Appendix replaces Section 2 of AS 3959 for NSW purposes.

24 August 2026 · Planning for Bush Fire Protection 2019, read 24 August 2026

What a BAL is actually measuring

The Rural Fire Service defines it as A means of measuring the severity of a building's potential exposure to ember attack, radiant heat and direct flame contact. The point worth holding onto is that a BAL is a measure of exposure, not of a building. It describes what the site can throw at a structure, and only then does it become a construction question: in the National Construction Code the BAL is used as the basis for establishing the requirements for construction to improve protection of building elements.

So the sequence runs one way. Assess the site, get a level, then build to what that level demands. A shutter is not BAL-40 rated in the abstract; it is offered as a way of meeting what BAL-40 requires of a window opening.

The bit that is free, and the bit that is not

This is the split that is worth knowing before you pay for anything. Appendix 1 of Planning for Bush Fire Protection 2019 states that The following methodology must be used to determine BALs and appropriate APZs, and that This Appendix replaces Section 2 of AS 3959 for the NSW clauses of both volumes of the National Construction Code.

Section 2 of AS 3959 is the standard's own method for determining a BAL. In NSW it is displaced. The method that actually applies sits in a document you can download from the RFS without paying, without an account and without a licence limiting you to one device.

Where each part of the process is published, in NSW

Step	Governing text	Cost to read
Determining the BAL for a site	Appendix 1, Planning for Bush Fire Protection 2019 (NSW RFS)	Free
What construction the BAL then requires	AS 3959	$286.63, one user, one device

For a window business this is a practical distinction rather than a technicality. Checking whether an assessment looks right, or understanding why a job came back BAL-29 rather than BAL-19, does not require buying the standard. Specifying compliant construction still does.

What the assessment looks at

The methodology is a site assessment, and its inputs are the land rather than the house. It begins by identifying vegetation: Identify all the vegetation formations for each aspect of the development within 140 metres, using the Keith (2004) vegetation classification, and that includes vegetation beyond the site boundaries as well as on it. Your neighbour's bush counts.

Then slope enters, and the combination rule is the one that surprises people. The combination of vegetation and slope that yields the worst case scenario shall be used. Where formations are mixed, the vegetation formation providing the greater hazard shall be used for the purpose of assessment.

That is a deliberately conservative design. An assessment does not average the aspects around a house or take the typical case; it takes the worst combination available and rates to that. Which is why a property with one bad aspect can carry a high BAL that looks disproportionate to someone standing in the driveway looking the other way.

What this page does not tell you

It does not tell you what BAL-29 or BAL-40 requires of a shutter, a screen or a window assembly, because those requirements are in AS 3959 and that text is licensed. We have not reproduced any of it and will not. It also describes NSW: the assessment methodology in Appendix 1 is stated to be the acceptable-solutions method applicable in NSW, and other states run their own planning arrangements, so do not carry this across a border.

And it is not a substitute for an assessment. A BAL for a specific property is determined by a qualified assessor against the actual site, not from a general description of the method.

How we made this

Read from Planning for Bush Fire Protection 2019, published by the NSW Rural Fire Service and downloaded free from the RFS website on 24 August 2026.

The document is typeset in two columns, and text extraction interleaves the columns mid-sentence. Every quoted phrase above is a short passage we confirmed reads contiguously in the source. We have deliberately quoted in fragments rather than stitching together a longer sentence the extraction cannot support, which is why some quotations here are shorter than they would otherwise be.

AS 3959 itself was not used. It is a licensed document, nothing in it is reproduced or paraphrased here, and the $286.63 figure comes from our own earlier reporting on the Standards Australia store rather than from the standard.

Sources

NSW Rural Fire Service, Planning for Bush Fire Protection 2019 (PDF, read 24 August 2026): the glossary definition of Bush Fire Attack Level as a means of measuring the severity of a building's potential exposure to ember attack, radiant heat and direct flame contact, and that in the NCC the BAL is used as the basis for establishing construction requirements; Appendix 1, Site Assessment Methodology, including that the methodology must be used to determine BALs and appropriate Asset Protection Zones, that it is the acceptable solutions methodology applicable in NSW, and that the Appendix replaces Section 2 of AS 3959 for the purposes of the NSW clauses of Volumes One and Two of the National Construction Code; and the assessment steps covering identification of vegetation formations within 140 metres per Keith (2004) including vegetation outside the site boundaries, the use of the formation providing the greater hazard where formations are mixed, and the rule that the combination of vegetation and slope yielding the worst case scenario shall be used.

Spotted an error in this explainer? Request a correction and we will check it against the RFS document and log the outcome here.