Fire performance is not one number. A specification can name non-combustibility, a Group number, a flammability index, a spread of flame index, a bushfire attack level or a fire resistance level, and they are different tests measuring different things. Some belong to the product, some belong to the tested system, and confusing the two is what gets a substitution rejected on site.
In short
- Non-combustibility is a material property. An FRL belongs to a tested system.
- A Group number to AS 5637.1 is about lining fire hazard, not about the batt behind it.
- BAL to AS 3959-2018 is a site condition, and the rating applies to the installed detail.
- Matching the R-value proves nothing about any of these.
- Ask which document the specification wants, then ask us for that document.
This is the part of a commercial specification that most often catches suppliers out, because everything else on the page is a number you can match and this is a set of documents you either have or do not.
Fire performance is not one number
When a specification says the insulation has to have "the right fire rating", it is usually pointing at one of these, and they are not interchangeable.
| What it is called | What it measures | Belongs to |
|---|---|---|
| Non-combustibility | Whether the material burns at all | The material |
| Group number, AS 5637.1 | Fire hazard of a wall or ceiling lining | The lining material |
| Flammability index | How readily the material supports flame | The material |
| Spread of flame, ignitability, heat evolved, smoke developed indices | Behaviour in the AS 1530.3 test | The material |
| Bushfire attack level, AS 3959-2018 | Exposure at the site, and what the construction must resist | The site, then the installed detail |
| Fire resistance level | How long an element resists fire, in minutes | The tested system |
Two products can both be described as "fire rated" and satisfy none of the same requirements. That is why the first question is always which document the specification is asking for.
Product property or system rating
This distinction decides who can answer the question, and it is the one worth internalising.
Product properties travel with the material. Non-combustibility, flammability index, the AS 1530.3 indices and a Group number are all determined by testing the product, and they appear on a datasheet.
System ratings belong to an assembly. A fire resistance level applies to a wall or floor as built, with a specific lining, framing, fixing pattern and insulation. Change any of those and you are outside the tested system, and the rating does not follow the batt.
Our own product notes say it plainly for the party wall products: fire performance belongs to the tested system rather than to the material on its own, so work from the specification for the wall and confirm the product suits it.
The practical rule: if the specification names an FRL, ask for the system. If it names a Group number or non-combustibility, ask for the product datasheet.
The indices, in plain English
AS 1530.3 produces a set of index numbers, and specifications quote them directly. Lower is better in every case.
- Ignitability index. How readily the material ignites.
- Spread of flame index. How far flame travels across the surface.
- Heat evolved index. How much heat the material contributes.
- Smoke developed index. How much smoke it produces.
A real example from our range makes the numbers concrete. Trade Select FireSark records a flammability index of 1, with ignitability, spread of flame and heat evolved indices all 0 and smoke developed at 2. Those four figures together are what a bushfire or non-combustible construction specification is looking for, not a single "fire rating".
Compare that with Trade Select ThermalBreak 7, which is Group 1 to AS 5637.1 with a Low flammability classification and suitability for all bushfire attack levels. Different product, different set of numbers, both legitimately described as having fire performance.
Group numbers
Group numbers come from AS 5637.1 and they classify the fire hazard of wall and ceiling linings, from Group 1 as the best performing through to Group 4.
Two things about them regularly cause confusion.
First, a Group number applies to the material that is exposed in the room, which is the lining. Insulation behind a lining is not usually the thing being classified, which is why some insulation products carry a Group number and many do not, and why the absence of one is not automatically a problem.
Second, where a specification does name a Group number for a product you are supplying, meeting the R-value is irrelevant to it. A product with the right R-value and no Group classification can be rejected, and that is a documentation problem rather than a performance one.
Our Kingspan Kooltherm K10 G2 and K10W soffit boards are an example of a product that carries the classification: NCC Group 2 to AS 5637.1, spread of flame index 0, smoke development 3 or lower, and FM 4880 approval for thicknesses 25 to 119 mm.
Bushfire attack level
BAL is different in kind from the others. It is not a property of a product at all, it is an assessment of the exposure at the site under AS 3959-2018, from BAL-LOW through to BAL-FZ, Flame Zone.
The site rating then drives what the construction has to resist, and products are described as suitable for particular levels when installed to specification. Two consequences follow.
Flame Zone is a different problem from the levels below it. At BAL-FZ the design is no longer about radiant heat alone, it is about direct flame contact and ember entry at the vulnerable edges of the building. That is why there are products made specifically for the detail rather than for the plane: our Fireseal FZ roof batts are cut 1200 x 115 mm to pack the roof edge, and are rated for continuous service to 650 °C.
The rating applies to the installed system. A membrane suitable for all BALs in a detail that does not match the specification is not delivering the rating. Several Bradford Thermoseal products are suitable for BAL 12.5 through to Flame Zone when installed to specification, and that qualifier is doing real work.
If your site is BAL rated, work from the bushfire report and the specification for the detail, and get independent advice before locking a sarking into a BAL design.
Non-combustible, and what it excludes
Where a specification calls for non-combustible material, it is asking for a specific material property and the choice narrows immediately.
In practice, that pushes you toward stone wool and glasswool. In the Bradford range the glasswool Gold products are the ones quoted as non-combustible, and stone wool is non-combustible by nature, which is why it turns up in party wall joints and Flame Zone details rather than as general insulation.
It equally rules things out. Polyester does the same thermal job at the same R-value and is the easier material to handle, but it is not the one carrying a non-combustibility claim, so it is not the substitution to make on a job that names one. Our comparison of insulation materials works through the trade-offs.
Note also that FireSark is described as non-combustible in both its components, the fibreglass fabric and the aluminium foil, and meets the Deemed-to-Satisfy provisions for non-combustible construction. That is a stronger claim than fire retardant, and the two phrases are not synonyms.
Getting a substitution approved
Substitutions are normal on commercial work. What gets approved is a request that shows the alternative meets every property the specification named, not just the thermal one.
- List what the specification actually asks for. R-value, and then each fire property separately.
- Show the specified product and the alternative side by side, property by property.
- Attach the documents. Product datasheet, evidence of compliance with AS/NZS 4859.1 for the thermal claim, and the relevant fire test report or classification.
- Say what it does to the Total R-value calculation, if anything.
- Where a system rating is involved, produce the system, not the product.
If you send us the specification we will tell you which products in our range carry the documentation it names, and where they do not, we will say so rather than hoping nobody checks.
What goes wrong
- Treating "fire rated" as one thing. Ask which test and which number.
- Substituting on R-value alone. The fire property is a separate requirement.
- Quoting a system rating as a product property. An FRL does not follow the batt into a different wall.
- Assuming a BAL rating covers any detail. It applies when installed to specification.
- Confusing fire retardant with non-combustible. Different claims, different evidence.
- Leaving the documentation to handover. The certifier will want it, and finding it late is how deliveries get rejected.
We supply it and we install it
AWBM carries non-combustible stone wool, glasswool, phenolic board and bushfire rated sarking across Victoria and New South Wales, and we install batts, wall wrap and sarking. Send the specification and we will tell you which products carry the fire documentation it names, then quote it supplied, or supplied and installed where it is batt, wrap or sarking work.
Or browse commercial insulation, building membrane and wall insulation.
Frequently asked questions
What does fire rated insulation actually mean?
It depends which test the specification is naming. It could mean non-combustible, a Group number to AS 5637.1, a set of AS 1530.3 indices, suitability for a bushfire attack level, or a fire resistance level for a system. They are different requirements and they are not interchangeable.
What is a Group number?
A classification under AS 5637.1 for the fire hazard of wall and ceiling linings, from Group 1 as the best performing. It applies to the material exposed in the room, which is usually the lining rather than the insulation behind it.
Is non-combustible the same as fire retardant?
No. Non-combustible is a material property meaning it does not burn, and it is what a specification asks for when it wants that assurance. Fire retardant is a different and weaker claim. Check which one the specification uses.
Which insulation is non-combustible?
Stone wool is non-combustible by nature, and in the Bradford range the glasswool Gold products are the ones quoted as non-combustible. Polyester does the same thermal job but is not the material carrying that claim.
Does a fire resistance level apply to the insulation?
Not on its own. An FRL belongs to the tested system, with its specific lining, framing, fixings and insulation. Change part of the system and the rating does not carry over.
What does BAL mean for insulation?
Bushfire attack level is an assessment of the site under AS 3959-2018, and it drives what the construction must resist. Products are described as suitable for particular levels when installed to specification, so the detail matters as much as the product.
What is different about BAL Flame Zone?
At Flame Zone the design problem is direct flame contact and ember entry rather than radiant heat alone, which is why products exist for specific details such as packing the roof edge, rated for continuous service at high temperature.
Can I substitute a product with the same R-value?
Only if it also meets every fire property the specification named. A product with the right R-value and no Group classification or no non-combustibility claim can be rejected, and that is a documentation issue rather than a performance one.
Can AWBM supply the fire documentation?
Yes. Send the specification and we will identify which products in our range carry the classifications and test reports it names, and tell you plainly where they do not.
Sources
- AS 5637.1, Determination of fire hazard properties, for the Group number classification
- AS 1530.3, Simultaneous determination of ignitability, flame propagation, heat release and smoke release
- AS 3959-2018, Construction of buildings in bushfire-prone areas
- AS/NZS 4200.1:2017, Pliable building membranes and underlays, for duty ratings
- AS/NZS 4859.1, Thermal insulation materials for buildings, for declared R-values
- NCC 2022 Volume One, Section J and the Deemed-to-Satisfy provisions for non-combustible construction
- Fire indices, classifications and BAL suitability from the Ametalin, CSR Bradford and Kingspan product data for the products listed above
General information, not a fire engineering opinion. Fire resistance levels and bushfire compliance belong to tested systems and to designs assessed for the specific site, so work from your project's fire and bushfire documentation and confirm any substitution with the fire engineer or certifier before ordering.