What This Requirement Covers
Balcony and podium waterproofing requirements set out the minimum design, materials and installation standards to prevent water ingress from horizontal external surfaces (balconies, terraces, podiums, roof terraces and similar) into the building fabric and spaces below. These requirements exist to protect structural elements, finishes and occupiable spaces from moisture damage, mould, corrosion and deterioration, and to ensure safe, durable performance of waterproofing systems over the expected service life.
The rules apply to designers, builders, certifiers and building owners responsible for new construction, alterations and repairs where a horizontal external surface is located above an internal space or otherwise requires a continuous waterproofing system. They cover what membranes may be used, how exposed joints and drainage must be detailed, acceptable substrates and fall/pitch, and referencing mandatory Australian Standards for materials and installation.
Key Requirements
- Mandatory membrane compliance: A waterproofing membrane for a roof, balcony, podium or similar horizontal surface must consist of materials complying with AS 4654.1 and be designed and installed in accordance with AS 4654.2, as required by NCC Volume One, F1D5 - External waterproofing membranes and NCC Volume Two, H2D8 - External waterproofing (NCC 2022).
- Where it applies: External waterproofing requirements apply to flat roofs, roof terraces, balconies and terraces located above internal spaces unless specifically exempted (see Exceptions). Refer to NCC Volume Two, H2D8 and NCC Volume One, F1D3-F1D5.
- Exposed joint protection: Exposed joints in a drainage surface must be protected in accordance with Section 2.9 of AS 4654.2 and must not be located beneath or run through planter boxes or water features (NCC Volume One, F1D4). Where exposed joints are subject to excessive movement (greater than 10 mm), additional measures such as a hob of minimum height 50 mm formed within the structural substrate and a discontinuous membrane are recommended (NCC Volume One, F1D4 explanatory information).
- Step-down requirements for concrete slabs: Balconies or terraces in some cases are not required to have membrane waterproofing if the structural concrete slab has a minimum step-down (recess) of 50 mm below the internal floor level, or where a suspended slab’s subfloor is not used and also has a 50 mm step-down (NCC Volume Two, H2D8(2)(b)(i)-(ii)).
- Drainage design: Stormwater drainage must be designed and constructed in accordance with AS/NZS 3500.3 (NCC Volume One, F1D3). Adequate falls to outlets and appropriate number/size of outlets are expected as per AS 4654.2 guidance.
- Materials and detailing: Membrane materials and associated components must comply with AS 4654.1 (material properties, compatibility and testing) and be installed and detailed per AS 4654.2 (substrate preparation, priming, laps, terminations, flashings, penetration details and protection layers).
- Exposed joint location guidance: Where possible locate exposed joints at a ridge or high point of the substrate to minimise water ingress risk (NCC Volume One, F1D4 explanatory information).
- Application to non-roof coverings: F1D3 to F1D5 exclusions exist for balconies where the flooring is timber/perforated decking or located directly above ground (NCC Volume One, F1D3-F1D5).
- References to other Standards and provisions: Typical related standards and guidance include AS 4654.1, AS 4654.2, AS 3740 (waterproofing wet areas - applicable where balconies connect to wet areas), and AS/NZS 3500.3 (stormwater drainage). Also consider ABCB Housing Provisions (Part 7.4) where referenced by state schedules for certain Class 1/10 situations (NCC Volume Two, H2D6 explanatory information).
Residential vs Commercial
- Residential (Class 1 and 10 as covered in NCC Volume Two):
- External waterproofing requirements in NCC Volume Two, H2D8 require membranes complying with AS 4654.1 and installed per AS 4654.2 where balconies or terraces are above internal spaces. However, balconies with timber or perforated decking or those directly above ground are excluded from F1D3-F1D5 application in NCC Volume One and H2D8 explanatory text. A concrete slab with a 50 mm step-down below internal floor level may also be excluded from membrane requirements (NCC Volume Two, H2D8(2)(b)(i)).
- The ABCB Housing Provisions may be referenced by certain states for gutter/downpipe sizing and roof drainage design for Class 1/10 buildings (NCC Volume Two, H2D6 explanatory info).
- Commercial / Multi-residential (Class 2-9 governed by NCC Volume One):
- More prescriptive application of F1D3-F1D5 applies for balconies, podiums and similar surfaces above internal spaces. Membranes must comply with AS 4654.1 and be installed per AS 4654.2 (NCC Volume One, F1D5). Exposed joints must be protected per Section 2.9 of AS 4654.2 and not run under planter boxes (NCC Volume One, F1D4).
- Podium decks that form part of fire-separation or other structural systems may require coordinated detailing with structural and fire engineering requirements. Always check relevant FRLs and structural design standards when waterproofing interfaces with fire or structural elements.
Exceptions and Exemptions
- No external membrane required where the flooring is timber decking or other perforated flooring or where the surface is directly above ground (NCC Volume One, F1D3-F1D5 exceptions).
- A concrete slab with a minimum 50 mm step-down below internal floor level can be treated as excluded from membrane requirements (NCC Volume Two, H2D8(2)(b)(i)).
- A suspended concrete slab whose subfloor is not used for habitable or non-habitable purposes and which has a 50 mm step-down below internal floor level may be exempt (NCC Volume Two, H2D8(2)(b)(ii)).
- Performance Solutions: Where a design does not meet the deemed-to-satisfy provisions, a Performance Solution using the NCC A2/A2G pathway may be submitted, demonstrating equivalence or superior performance. Where alternative materials or systems are proposed, evidence should reference test data, manufacturer instructions and Accredited Practitioner design where required (NCC Volume Two, H2D8 explanatory info).
State and Territory Variations
- The NCC requires states and territories to include schedules that may modify national provisions. For example, Victoria’s schedule gives detail on acceptable guttering/downpipe options and may allow ABCB Housing Provisions alternatives for Class 1/10 buildings (NCC Volume Two, H2D6(1) - VIC H2D6(1) and VIC H2D6(3)).
- Queensland, NSW, WA, SA, TAS, ACT and NT may each have specific clarifications or additional requirements in their NCC schedules affecting roofing, drainage or podium treatment. Users must check the relevant state schedule in NCC 2022 Volume One (Schedules 4-12) for jurisdictional modifications as required by the NCC schedule notes.
- Note: State schedules can alter acceptable documents, referenced standards or add local requirements for stormwater runoff sizing, planter detailing, or maintenance access. Always verify against the applicable state schedule in the NCC 2022 Volume One.
Practical Compliance Tips
- Follow AS 4654.1 and AS 4654.2 exactly - these are the primary standards for material selection and detailing; manufacturer instructions should align with these Standards.
- Provide adequate falls to outlets and multiple outlets where required; ponding is a common cause of membrane failure. Check AS 4654.2 guidance and AS/NZS 3500.3 for drainage design.
- Protect exposed joints: avoid locating construction or movement joints under planters or water features; if unavoidable, use the Section 2.9 details in AS 4654.2 and consider a 50 mm hob where movement exceeds 10 mm (NCC Volume One, F1D4).
- Coordinate trades early: slab formation, screeds, membranes, flashings, balustrade connections and drainage must be coordinated to avoid cutting or penetrating membranes later.
- Select compatible materials: check chemical compatibility between primers, adhesives, membranes and coatings per AS 4654.1 to avoid premature degradation.
- Document performance evidence for alternative systems: if using a proprietary system or proposing a Performance Solution, compile test data, durability evidence and installer accreditation to support compliance with the NCC.
- Allow access for inspection and maintenance: detail fall heads, outlets and access points so future maintenance is practical; poorly maintained outlets are a frequent cause of leaks.
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