Sarking and Building Wrap Requirements for Walls and Roofs

What This Requirement Covers

This requirement covers the use of pliable sarking-type materials, building paper and building wraps installed as weatherproofing, vapour control and incidental thermal layers on external walls and under roof coverings in buildings regulated by the National Construction Code (NCC) in Australia. It explains why these materials are regulated (weather-tightness, condensation control, fire hazard properties and integration with insulation), where they must be located in the wall or roof assembly, the relevant performance and deemed-to-satisfy provisions, and the standards that sarking and building wrap products must meet. It applies to designers, builders, installers, building surveyors/certifiers and homeowners involved in the design, specification and construction of external envelope systems for Classes 1 to 10 buildings under the NCC.

Sarking and building wrap requirements exist to reduce the risk of water penetration, control vapour transport and condensation, contribute to the thermal performance of the building envelope when used with insulation, and manage fire hazard properties of pliable membranes. Correct selection and installation affects durability of cladding, compliance with thermal and condensation provisions in the NCC, and fire safety requirements that sometimes differ by building class and by state or territory variations.

Key Requirements

1. Applicable NCC provisions: Sarking-type materials and building membranes are required to comply with AS 4200.1 and be installed in accordance with AS 4200.2, as specified in NCC Volume One, F3D3 and related clauses. The NCC also sets fire hazard and vapour permeance requirements where these materials are placed on the exterior side of the primary insulation layer (see Verification Methods and Deemed-to-Satisfy provisions cited below). Cite: NCC Volume One, F3D3; F8P1 (Verification/Deemed-to-Satisfy provisions).
2. Material standard: Sarking-type material used for weatherproofing of roofs and walls must comply with AS 4200.1 (Pliable building membranes and underlays, Part 1: Materials) and be installed in accordance with AS 4200.2 (Installation). Cite: NCC Volume One, F3D3; F8P1.
3. Location relative to insulation: Where a pliable building membrane, sarking-type material or insulation layer is installed on the exterior side of the primary insulation layer of an external wall it must have a minimum vapour permeance as required by the NCC (see F8P1). Cite: NCC Volume One, F8P1.
4. Vapour permeance and condensation control: The NCC requires membranes on the exterior side of the primary insulation to have a vapour permeance not less than a specified value in the Verification/Deemed-to-Satisfy methods (refer to F8P1 and the corresponding Verification Methods in NCC Volume One for the exact numerical vapour permeance requirements applicable to the situation). Cite: NCC Volume One, F8P1.
5. Fire hazard properties: For Class 10 buildings, sarking-type materials used in roofs must have a Flammability Index not greater than 5, as stated in NCC Volume Two (Housing Provisions). Sarking and pliable membranes are subject to the NCC fire hazard provisions and Specification C or the relevant Specification for fire hazard properties where required (see NCC Volume One Specification 14 and relevant Housing Provisions). Cite: NCC Volume Two H3D3 (and related Housing Provisions); NCC Volume One Specification 14.
6. Roof coverings and sarking: Roof coverings must comply with the applicable roof material standards (for example AS 1562.1 for metal sheet roofing, AS 2049 for roof tiles), and where sarking is used as an underlay it must comply with AS 4200 series and the roof manufacturer/flashings/installation details required by NCC Volume One, F3D2-F3D3 and NCC Volume Two figures (for example H1D7 shows sarking position in typical roof sections). Cite: NCC Volume One F3D2-F3D3; NCC Volume Two H1D7.
7. Wind and fixings: Where sarking is part of the roof/wall system, relevant wind classification and fixing requirements follow the roof/cladding standards such as AS 1562.1, AS 4040 family for openings testing and AS 1684 for timber-framed structures where applicable. Designers must ensure sarking and underlays do not compromise required resistance to wind-driven rain and wind loads specified elsewhere in the NCC and referenced Australian Standards. Cite: AS 1562.1; AS 1684 (where framing or fixings are referenced in NCC clauses).
8. Other referenced standards: Use of sarking and building wraps interfaces with other NCC requirements and Australian Standards such as AS 2047 for windows and water penetration resistance, AS 4254.1 for flexible ductwork where applicable, and fire-related requirements in Specification 14. Cite: NCC Volume One F3D4; Volume Two H3D3; NCC Volume One Specification 14.

Residential vs Commercial

1. Residential (Class 1 and 10) buildings: The NCC Housing Provisions (NCC Volume Two) include specific deemed-to-satisfy provisions addressing sarking, underlays and vapour/condensation control for houses, townhouses and associated Class 10 structures. For Class 10 roof sarking, the requirement that roof sarking have a Flammability Index not greater than 5 applies. Installation in housing is commonly specified to AS 4200.2 and activation of condensation risk mitigation is typically done by placing the wrap on the exterior side of the primary insulation as required by NCC Volume Two/Housing Provisions. Cite: NCC Volume Two H3D3; AS 4200.2.
2. Commercial (Class 2 to 9) buildings: NCC Volume One contains the performance and deemed-to-satisfy provisions that apply to multi-unit residential buildings and non-residential buildings. The same requirement to use sarking that complies with AS 4200.1 and install it in accordance with AS 4200.2 applies, but additional fire hazard, smoke and durability considerations are often stricter for higher class buildings (for example Specification 14 and clauses addressing fire hazard properties and where sarking may be exempted from some fire hazard rules). Designers must also confirm compliance with building classification specific FRLs, sprinkler provisions and state schedules where fire performance is affected. Cite: NCC Volume One F3D3; Specification 14.

Exceptions and Exemptions

1. Materials explicitly listed in the NCC as exempt from particular fire hazard requirements (for example plaster, cement render, concrete and certain other assemblies) are excluded from some Specification 14 controls - consult NCC Volume One Specification 14 for the complete list and any conditions. Cite: NCC Volume One Specification 14.
2. Where a pliable membrane is used internally, or not located on the exterior side of the primary insulation, different vapour permeance rules apply - the vapour permeance requirement in F8P1 applies specifically when the membrane is exterior to the primary insulation layer. Cite: NCC Volume One, F8P1.
3. Alternative solutions are permitted under the NCC where a performance solution can demonstrate equivalence to the performance requirements. This could include proprietary membranes with test evidence for water penetration, vapour control and fire hazard properties or system solutions (flashing, drainage planes, integrated cavity systems) proven by test or expert judgement. Cite: NCC Volume One (Performance Requirements and Verification Methods).

State and Territory Variations

1. The NCC is national, but each state and territory may include specific schedules that modify or add to national provisions. For example, Victoria, Queensland and others include state schedules in NCC Volume One Schedules 4-12 that may alter requirements for cladding, fire hazard treatments or the way verification is demonstrated. Always check the relevant state schedule in NCC 2022 Volume One (Schedules 4-12) for local amendments. Cite: NCC Volume One, Schedules 4-12.
2. Some jurisdictions have heightened controls on external wall cladding and combustible materials following major cladding safety reviews; these can affect acceptance of certain sarking or wrap products when used in conjunction with external cladding systems on higher buildings. Check your state schedule and any recent ministerial directions or codes of practice. Cite: NCC Volume One - State Schedules (Schedules 4-12).

Practical Compliance Tips

1. Specify compliant products - Only use sarking and building wrap products with documented compliance to AS 4200.1 and installation instructions matching AS 4200.2; retain manufacturer data sheets and test reports on site.
2. Place membranes correctly - Install the membrane on the exterior side of the primary insulation where required by NCC Volume One, F8P1, and ensure vapour permeance meets the value required for the assembly to avoid condensation issues.
3. Check fire properties - For Class 10 roofs ensure roof sarking has Flammability Index ≤ 5 as required in NCC Volume Two H3D3; for other classes review Specification 14 exemptions and required fire hazard tests in NCC Volume One.
4. Integrate flashings and junctions - Water penetration problems usually occur at junctions. Coordinate sarking with window flashings (AS 2047), eaves, penetrations and cladding to provide a continuous drainage plane and comply with NCC Volume One F3D3 and F3D4.
5. Follow installation standard - Install to AS 4200.2 and the roof/cladding manufacturer’s instructions; improper fixings, laps and sealing are common noncompliance issues.
6. Record and provide evidence - Keep documentation showing product compliance, installation instructions and on-site photos; certifiers commonly request this evidence during assessment against NCC Volume One and Volume Two requirements.
7. Check state schedules and project class - Before specifying membrane types confirm any state schedule amendments in NCC Volume One Schedules 4-12 and verify applicable fire and performance requirements for the building class (Class 1-10) and building height.

References (selective)

1. NCC 2022 Volume One - Building Code of Australia: F3D2, F3D3, F8P1, Specification 14 and state schedules (Schedules 4-12).
2. NCC 2022 Volume Two - Housing Provisions: H1D7 (typical roof section), H3D3 (Flammability Index for Class 10 sarking) and related deem-to-satisfy provisions.
3. AS 4200.1 and AS 4200.2 - Pliable building membranes and underlays (materials and installation).
4. AS 1562.1, AS 2049, AS 2047, AS 1684 and AS 4254.1 where these standards interface with roofing, cladding and ductwork requirements.

Note: This article summarises the key NCC references and standards affecting sarking and building wraps. For a project-specific compliance determination, consult the full NCC clauses and tables cited above and any applicable state schedule, or engage a registered building certifier or specialist if uncertainty remains.