Sarking and membranes are permitted in non-combustible facade assemblies under the NCC, provided they meet the specific concession criteria in C2D10(6)(f): the material must be less than 1mm thick and have a Flammability Index of not more than 5 when tested to AS 1530.2. This allows compliant polymer-based membranes to sit within an otherwise fully non-combustible wall assembly without triggering a Performance Solution.
That is the short answer. The detail - and the practical considerations around it - is worth understanding properly, because sarking and membrane selection is one of the areas where facade assemblies get tripped up during certification review.
Why Is There an Apparent Conflict?
For Type A and Type B construction under the NCC, external wall assemblies are generally required to be constructed from non-combustible materials. The Deemed-to-Satisfy provisions in C2D10 set out what materials are acceptable and what concessions apply.
Sarking and membranes - the flexible sheet materials installed behind rainscreen cladding for waterproofing, air sealing, and vapour management - are almost universally polymer-based. Polyethylene, polypropylene, and similar polymers are the standard substrate for building wraps and wall membranes across the Australian market. These materials are combustible. They will not pass AS 1530.1.
This creates what appears to be a contradiction: the wall assembly must be non-combustible, but the membrane that protects it from moisture is inherently combustible. Removing the membrane to resolve the contradiction is not a practical option - the membrane serves functions that are critical to the long-term performance of the wall.
The NCC anticipated this. The concession in C2D10(6)(f) exists specifically to address it.
What Does C2D10(6)(f) Actually Say?
The concession permits “sarking-type material” within a non-combustible external wall assembly where the material is:
- Less than 1mm thick, and
- Has a Flammability Index of not more than 5 when tested to AS 1530.2.
Both criteria must be met. A membrane that satisfies one but not the other falls outside the concession.
AS 1530.2 is the standard for measuring the Flammability Index of materials. It assesses how a material behaves when exposed to a radiant heat source - specifically, how readily it ignites and how far flame spreads across its surface. A Flammability Index of 5 or less indicates a material that, while technically combustible, presents very limited fire contribution.
The practical effect of this concession is significant. It means that a compliant sarking or membrane can be incorporated into a non-combustible facade assembly under the DtS pathway without requiring a Performance Solution. The assembly remains DtS-compliant. The compliance documentation remains straightforward.
What Does the Full Non-Combustible Assembly Look Like?
The C2D10(6)(f) concession for sarking does not stand alone. It works within the context of the complete wall assembly, where every other component must also satisfy the non-combustibility requirements.
In a typical rainscreen facade assembly using aluminium cladding, this means:
Cladding panels - interloQ interlocking rainscreen panels and element13 solid aluminium panels are both tested to AS 1530.1 by CSIRO and confirmed as non-combustible. The aluminium cladding is the outer skin of the assembly and the first line of weather defence.
Insulation - must be non-combustible. Mineral wool, glass wool, and stone wool all satisfy AS 1530.1. Polystyrene (EPS, XPS) and polyurethane foam insulation boards do not. This is a common specification error - selecting an insulation product based on thermal performance without checking its combustibility classification. If the insulation is combustible, the assembly does not comply via DtS, regardless of the cladding or membrane selection.
Subframe, brackets, and fixings - aluminium, steel, and stainless steel are non-combustible. Timber battens are not. The subframe connects the cladding to the structure and sits within the ventilated cavity, so it must satisfy the same non-combustibility requirements as the rest of the assembly.
Sarking/membrane - permitted to be combustible under the C2D10(6)(f) concession, provided it meets both the thickness and Flammability Index criteria.
The assembly compliance is only as strong as its weakest component. Every element needs to be checked, not just the cladding.
What Functions Does the Membrane Serve?
The membrane behind rainscreen cladding is not optional. It performs three functions that are fundamental to the wall assembly’s performance over the life of the building.
Secondary waterproofing. The rainscreen principle accepts that some water will penetrate the outer cladding skin - through joints, laps, and pressure differentials. The membrane provides the secondary line of defence, directing that water downward and outward through the drainage cavity before it can reach the substrate or insulation.
Air barrier. The membrane reduces uncontrolled air leakage through the wall assembly. This matters for both energy performance (Section J of the NCC) and occupant comfort. An air-leaky wall assembly undermines insulation performance regardless of the R-value of the insulation itself.
Vapour management. Depending on the climate zone and wall construction, the membrane may need to manage vapour diffusion - allowing moisture vapour to migrate outward while preventing bulk water from penetrating inward. Getting this wrong can lead to interstitial condensation within the wall, which causes long-term damage to substrates and framing that is invisible from either side.
Removing the membrane to simplify the combustibility question would compromise all three functions. It is not a viable approach.
How Do You Select a Compliant Membrane?
Not all building wraps and wall membranes on the Australian market meet the C2D10(6)(f) criteria. Specifiers must verify two things from the membrane manufacturer’s documentation:
Flammability Index to AS 1530.2. The manufacturer’s test report must show an FI result of 5 or less. This is a specific test result, not a general fire rating or classification. Ask for the AS 1530.2 test report - not a brochure claim, not a general fire performance statement, but the actual test report with the FI value.
Thickness under 1mm. Most standard building wraps fall well under this threshold, but it needs to be confirmed rather than assumed. Some self-adhered or multi-layer membrane products may approach or exceed 1mm. If the product is 1mm or thicker, it falls outside the concession entirely.
Major membrane manufacturers in Australia produce products that meet both criteria, and many specifically market their products as NCC-compliant for use in non-combustible assemblies. But verification is essential. The responsibility for confirming compliance sits with the specifier, and the certifier will expect to see the evidence.
What Are the Common Mistakes?
Several recurring issues come up on projects where sarking and membrane compliance is questioned during certification.
Specifying a membrane without checking the FI value. The most common error. A membrane is selected based on waterproofing performance, brand familiarity, or installer preference - and nobody checks whether it meets the C2D10(6)(f) Flammability Index requirement until the certifier asks for the documentation.
Not requesting the AS 1530.2 test report. Product data sheets sometimes reference fire performance in general terms without stating the specific FI value to AS 1530.2. General statements are not sufficient for certification. The test report is the evidence.
Using a membrane thicker than 1mm. Less common with standard building wraps, but relevant for self-adhered membranes, liquid-applied membranes, or multi-layer products. If the product exceeds 1mm, the DtS concession does not apply, and the project either needs a different product or a Performance Solution.
Incomplete installation. Even a compliant membrane must be installed correctly to function. Laps must be adequate - typically 150mm minimum, though manufacturer specifications may require more. Penetrations for services, brackets, and fixings must be sealed. The membrane must be continuous across the wall face and turned into window and door openings to maintain the weatherproofing line. Gaps and unsealed penetrations compromise the drainage function and may create moisture paths that bypass the membrane entirely.
What Should Certifiers Ask For?
For certifiers reviewing a non-combustible facade assembly that includes a sarking or membrane layer, the documentation checklist is straightforward:
- The membrane manufacturer’s AS 1530.2 test report showing a Flammability Index of 5 or less.
- Confirmation of the membrane thickness (less than 1mm).
- The cladding AS 1530.1 test report confirming non-combustibility (for Valmond & Gibson systems: CSIRO reports FNC12595 for interloQ, FNC12545 for element13).
- Insulation AS 1530.1 test report or classification.
- Confirmation that the subframe, brackets, and fixings are non-combustible (aluminium, steel, or stainless steel).
This documentation should form part of the facade compliance pack submitted for the project. Where all components are covered, the assembly satisfies DtS via C2D10 without requiring a Performance Solution.
Where Does Valmond & Gibson Sit in This?
Our compliance documentation covers the cladding system - the aluminium panels, the fixing methodology, and the structural and weather performance of the installed system. AS 1530.1 reports, weather testing to AS/NZS 4284, structural calculations, and coating warranties are all part of the standard compliance pack we provide for every project.
The membrane selection is typically specified by the architect or facade engineer as part of the broader wall assembly design. The certifier verifies compliance of each component. Valmond & Gibson can advise on typical compatible assemblies and confirm which membrane products we have seen used successfully alongside our systems, but the membrane specification responsibility sits with the design team.
This is a deliberate boundary. The membrane interacts with the substrate, the insulation, the climate zone, and the vapour profile of the wall - all factors that are specific to the project and the design intent. The right membrane for a coastal high-rise in Brisbane is not necessarily the right membrane for an inland institutional building in Canberra. The design team is best placed to make that call.
The Key Takeaway
The NCC provides a clear, workable pathway for including sarking and membranes in non-combustible facade assemblies. The C2D10(6)(f) concession is not obscure or ambiguous - it is a specific provision designed for exactly this situation. The requirements are straightforward: under 1mm thick, Flammability Index of 5 or less to AS 1530.2.
The practical discipline is in verifying compliance at specification stage - not at certification review, when a non-compliant membrane selection can cause delay and cost. Check the test data early, include it in the compliance pack, and the sarking question resolves itself.
Need compliance documentation for an upcoming facade project? Our team can provide full testing reports and compliance packs for any V&G system. Talk to our team.
Related Reading
- Cavity Barriers in Facade Systems: When Does the NCC Require Them?
- Non-Combustible vs Fire Retardant: The NCC Distinction
- Ventilated Facade Design: Principles and Performance
- Flashing and Waterproofing at Cladding Junctions
Last updated: 4 April 2026