What is the definition of a non-combustible wall?

Non-combustible as defined by the BCA means:

  • Applied to a material – not deemed combustible as determined by AS 1530.1 – Combustibility Tests for Materials; and
  • Applied to construction or part of a building – constructed wholly of materials that are not deemed combustible.

However, the term ‘wall’ is not defined in the BCA. When a term is not specifically defined in the Code, the common usage governs. The following definitions are from the Macquarie dictionary:

  • Wall – an upright work or structure of stone, brick or similar material, serving for enclosure, division, support, protection etc., as one of the upright enclosing sides of a building; or anything which resembles or suggests a wall.

Why are non-combustible walls required?

The BCA stipulates critical elements of a building to be non-combustible, so that in the event of a fire, the failure of these components or elements will not cause or allow, for example, the building to collapse, escaping residents to be trapped, or the fire to travel to other buildings or to other sections of the same building, which are on an adjacent level or otherwise separated.

What materials are regarded as non-combustible by the NCC?

NCC 2019 Part C1.9 (e) lists materials that can be regarded as non-combustible. Note that some of these materials have combustible components:

  1. Plasterboard.
  2. Perforated gypsum lath with a normal paper finish.
  3. Fibrous-plaster sheet.
  4. Fibre-reinforced cement sheeting.
  5. Pre-finished metal sheeting having a combustible surface finish not exceeding 1mm thickness and where the Spread-of-Flame Index of the product is not greater than 0.
  6. Sarking-type materials that do not exceed 1mm in thickness and have a Flammability Index not greater than 5.
  7. Bonded laminated materials where—
    1. each lamina, including any core, is non-combustible; and
    2. each adhesive layer does not exceed 1mm in thickness and the total thickness of the adhesive layers does not exceed 2mm; and
    3. the Spread-of-Flame Index and the Smoke-Developed Index of the bonded laminated material as a whole do not exceed 0 and 3 respectively.

What constitutes a non-combustible wall, or what elements must be non-combustible?

The best source to refer to here is the ABCB Advisory Note on ‘Fire performance of external walls and cladding’ dated 3/2/2020.

Note that all ABCB Advisory Notes are full of disclaimers and exclusions of liability, but nevertheless the following is stated on page 3 and 4:

“A building element is considered to be part of an external wall if it is integral (i.e. is not ancillary) to the construction of the wall. For example, the following elements are considered to be part of an external wall:

  • Facade covering (e.g. render and external cladding)
  • Framing
  • Insulation
  • Sarking
  • Spandrels
  • Internal lining (e.g. plasterboard) of an external wall.

In most instances, a curtain wall system would be considered to be an external wall, and a render system would be considered an integral part of an external wall.

Minor elements commonly attached to an internal lining of an external wall, such as skirting boards and cornices, would not be considered a part of the wall because they are not integral to the wall.”

So far, so good, but due to the complexity of modern designs and construction methods, this is not sufficiently clear for determining a permissible attachment, or what is not constituted part of a non-combustible wall.

When is an attachment to a non-combustible wall not regarded as part of the wall?

The next clue we have is the BCA definition of Ancillary element, which is “an element that is secondary to and not an integral part of another element to which it is attached.”

CSIRO, in their publication Fire safety guideline for external walls dated 18.4.2016, applies the following reasoning to determine when a building element should be assessed as an external wall (or integral part of external wall) or an attachment:

  • If the cladding/lining/other item is removed and the remaining structure no longer functions suitably as an external wall (e.g., the remaining structure has no fire resistance level, is unable to prevent the penetration of water, is unable to resist wind loads or in certain applications cannot meet acoustic requirements), then it is considered an integral part of the external wall.
  • If the cladding/lining/other item is removed and the remaining wall still functions as an external wall then it can be regarded as an attachment.

What can be fixed to a non-combustible wall?

Thus, attachments to a non-combustible wall are allowed. What is still not clear is whether these can be of combustible materials, e.g. timber, or not.

We need to refer again to the ABCB Advisory Note on “Fire performance of external walls and cladding” dated 3/2/2020. On page 4 and 5 it clearly states:

“1.3.2 Permitted ancillary elements

C1.14(a) permits any ancillary element that is non-combustible, as determined by testing in accordance with AS 1530.1, to be fixed, installed or attached to the internal parts (i.e. within) or external face of an external wall required to be non-combustible.

The ancillary elements listed in C1.14(b) to (m), even though combustible, can also be fixed, installed or attached to an external wall required to be non-combustible, provided they comply with any specified limitations or conditions. Some of these limitations or conditions are explained in sections 1.3.3 and 1.3.4 below.

1.3.3 Combustible signs

1.3.4 Combustible awnings, sunshades, canopies, blinds and shading hoods”

More detailed requirements are then listed in the case of 1.3.3 and 1.3.4.

This article helpfully clarifies the following:

“There are minor building and decorative elements often fixed or attached to an internal lining, such as:

  • skirting boards
  • cornices
  • architraves
  • power points, and
  • switches

These elements do not function as the internal lining, nor are they integral parts of the internal lining or the wall. As such, by virtue of not being a part of the wall, they are not subject to the requirements of C1.9(a)(i) to be non-combustible when installed as part of the internal lining to an external wall.”

Unfortunately for us, though, there is no definition of minor in the BCA, so we are still dealing with a subjective interpretation.

There is an argument that the concern relates to items on the outside of a building, as it is well known the issues relating to fires spreading up the outside of a building due to combustible cladding as happened at Grenfell Tower and in other fires.

Thus, some fire engineers will allow the use of combustible attachments on the inside face of a non-combustible wall, if they meet the definition of an ancillary element or attachment, and meet the usual requirements of C1.10 relating to internal linings.

However, there is no statement given whatever to say that these restrictions apply only to attachments to the external face of a non-combustible wall; rather, the opposite has been stated.

Supawood recommends the following, which you would need to do on a project-by-project basis:

1. Ask your building certifier or surveyor if he will allow combustible attachments to non-combustible walls in your building. He may want full details of each attachment and assess each one separately.

2. If your building certifier or surveyor does not allow the attachment, you have two options:

a. Specify a non-combustible equivalent e.g. Supawood non-combustible linings made of aluminium.

b. Advise your client he may wish to add an attachment himself e.g., a pinboard after he has received Occupation Certification.