Unless you are building or renovating a home in a bushfire prone area, combustibility of building materials may not necessarily be front of mind.
Yet, in the wake of the catastrophic 2019-2020 bushfire season that burnt 18.6 million hectares, destroyed 5,900 buildings and killed 34 people, many are asking how we build safer and more resilient homes.
As well as bushfires, the disastrous effects of combustible cladding and other building materials have prompted several governments around the world, including Australia, to include non-combustible provisions for certain construction types in certain applications.
The fact is though, when it comes to designing out fire risk, be it for bushfire resilience or high rise apartments, the requirements under the National Construction Code (NCC) are considered by many to be “skin-deep”. It is still possible to install combustible materials in certain applications, which leaves residents exposed to unnecessary fire risk and their homes less resilient.
Photograph: Shutterstock
While the NCC sets out non-combustible Deemed-to-Satisfy provisions for internal and external walls in all Type A and Type B construction types, they fall short for ceilings and other construction types where the risk of ignition and fire spread remains prevalent.
In this post, we maintain that choosing a non-combustible insulation material, such as Earthwool®, should be a requirement for all construction types, not just Type A and Type B, and for ceiling applications, not just internal and external walls to ensure fire risk is kept at a minimum.
Designing out fire risk using the fire triangle principle
There are three elements required to ignite and maintain a fire: heat, fuel and oxygen. Removing any one of these will likely extinguish a fire or mitigate the risk of ignition in the first instance.
What direction does fire spread?
Fire commonly travels vertically however its direction of spread is largely determined by the orientation of its fuel source.
Fire burns vertically due to the upward fuel orientation, however fire can also burn in horizontal and adjacent directions when a fuel source is present. In the instance of a match, the fire will spread faster due to the continual heat in direct contact with the fuel, however, the match will still burn when held horizontally, or in other orientations.
Figure 1 depicts the intensity of the flame for each orientation of an ignited match.
Figure 1: Fuel orientation and its effect on flame spread
Current National Construction Code non-combustibility requirements
The National Construction Code of Australia (NCC 2019, Vol.1, C1.9) details external wall requirements for commercial buildings based on the building class and the height of the building in storeys. This is used to determine the Type of construction as either Type A, Type B, or Type C to be assigned to the building in order to determine the Deemed to Satisfy (DtS) requirements of the NCC. Both Type A and Type B construction require non-combusitble external walls using components tested in accordance to AS 1530.1. However, Type C buildings currently allow combustible components (including insulation materials) to be permitted for use. Taller buildings, especially those with higher risk occupants, require stringent fire performance requirements due to the length of time it takes to reach safety at the ground level.
As shown in Table 1, Type A construction is for projects three storeys and greater, while Type B construction is for projects two to three storeys. Such projects include apartments (Class 2), office buildings (Class 5), hospitals (Class 9a), public assembly buildings such as tertiary buildings (Class 9b), and aged care buildings (Class 9c).
Table 1: Commercial building classifications and construction types
In accordance with the NCC, both Type A and Type B construction projects require external walls and common walls to be constructed using non-combustible materials, including insulation materials. Manufacturers are required to be compliant with non-combustibility standard AS 1530.1, particularly for external wall applications.
It is critical for all stakeholders of a project to be conscious of products fire performance, as liability does not solely fall upon the fire engineer. For example, after the Lacrosse building fire in Melbourne in 2014, legal proceedings found that despite the fire igniting from a resident’s un-extinguished cigarette, the choice and installation of unsuitable materials was also to blame. The court ordered that damages be shared between the fire engineer (39%), building surveyor (33%), the architect (25%), and the resident (3%)1.
Regulatory requirements for walls to include non-combustible building elements effectively remove a fuel source for potential fires and is a great example of the fire triangle principle in action. Without a fuel source such as flammable or non-regulatory construction materials, heat sources such as cigarettes are far less likely to cause a fire to ignite and spread. However, risk can be mitigated further by applying this non-combustible requirement to additional applications such as soffits, and roofs where the risk of ignition is still prevalent.
Alternatively, performance solutions are a method that enables the use of combustible materials in Type A and Type B project types. This method is a combination of system tests and professional evaluations of suitability, However, risk is retained due to site conditions which often make it difficult to install products to the same standard of the that during the system test.
The 2014 fire at the Lacrosse tower in Melbourne’s Docklands spread across the facade in a matter of minutes.
Photograph: Gregory Badrock/Metropolitan Fire Brigade
What about roof and soffit applications?
Materials that are combustible currently use a Group number test, in accordance with AS 5637.1, to comply with the building standards of Australia. This standard involves a full room corner burn test with insulation materials installed to both the walls and ceiling of a rectangular test rig.
A common inconsistency associated with AS 5637.1 testing is that the time allowed (20 minutes) for the initial Group number test will rarely equate in comparison to real-life situations allowing highly combustible products to be approved and installed. Ultimately, testing designed to determine a products combustibility should continue until the product fails, as building fires are rarely extinguished before 20 minutes.
While the room corner burn is an effective test to determine the smoke development of a product when exposed to an open source of fire, it does allow manufacturers to engineer materials to meet minimum standards rather than mitigate the risk entirely. An example of this is foam insulant manufacturers increasing the thickness of the foil facing. This extends the time it takes for flame in the full room burn test to make contact with the combustible bulk insulation component of the foam insulation panels. This is of great concern because specific installation guidelines must be strictly adhered to in order to meet compliance. The continued use of combustible materials in soffits therefore retains the fuel source element of the fire triangle, which in turn creates greater risk for the likelihood of fire occurrence in comparison to installing non-combustible products.
Knauf Insulation products that are engineered for use in soffits and roof applications have been rigorously tested in accordance with AS 5637.1 (as required by the NCC 2019) and have received a Group 1, the highest possible Group rating.
Knauf Insulation products that are engineered for use in soffits and roof applications have been rigorously tested in accordance with AS 5637.1 (as required by NCC 2019) and have received a Group 1, the highest possible Group rating.
The following Knauf Insulation products have undergone further testing and achieved an additional “non-combustible” performance rating in accordance with AS 1530.1:
Combustible vs. Non-combustible
To demonstrate the effectiveness of Knauf Insulation non-combustible products, Table 2 compares the performance of SprayWool Thermal and Acoustic with PIR (Polyisocyanurate) Panels.
Table 2: Comparison of Group 1 testing to AS 5637.1
In the SprayWool image, the product is shown to produce far less smoke in comparison to the PIR product, and the lower intensity of the flame is clearly visible. This demonstrates that the non-combustible product’s performance greatly exceeds that achieved by foil faced foam insulant boards, when used in soffit and roof applications.
Currently in Australia there are multiple applications where a product with a Group 2 rating or higher can be used. This not only amplifies the risk of fire occurring in the first instance, but also adds potential hazards for emergency services when entering buildings in the unfortunate event of a fire. Selecting a Group 1 and non-combustible product will effectively design out the risk of fire at the earliest stage of the project.
You can download a printable version of this Technical Bulletin here, or to learn more, please visit our section on non-combustible insulation solutions.
*1 Dunstan, J., 2021. Fire engineer, architect and surveyor wear $5.7m of damages from flammable cladding blaze. [online] Abc.net.au. Available at: https://www.abc.net.au/news/2019-02-28/lacrosse-apartment-owners-win-5.7-million-cladding-fire-damages/10857060 [Accessed 1 July 2021].