Bathroom Renovation Waterproofing and Compliance

What This Requirement Covers

Bathroom waterproofing requirements in the National Construction Code (NCC) and related Australian Standards set minimum measures to prevent water penetration into building elements, protect structural fabric and finishes, and maintain occupant amenity in wet areas. They exist because persistent moisture ingress causes rapid deterioration of substrates, mold growth, hygiene problems and structural damage that can be costly or unsafe. These rules apply to designers, builders, certifiers and homeowners undertaking new work, alterations or renovations to bathrooms, showers, laundries, WC rooms and similar wet areas.

Requirements are expressed as a mix of Performance Requirements in NCC Volume One and Volume Two, Deemed-to-Satisfy provisions, and referenced Standards (notably AS 3740 and AS 4654). The ABCB Housing Provisions in the NCC Volume Two set out specific wet-area detailing for Class 1 and 10 buildings. Compliance affects choice of materials, membrane systems, substrate preparation, junction and penetration treatments, and finished heights of waterproofing.

Key Requirements

1. Applicability: Applies to wet areas in buildings as set out in NCC Volume One and Volume Two - see F2D2, F2P1 and related provisions for Classes 2, 3 and Class 4 parts; ABCB Housing Provisions Part 10.2 applies for Class 1 and 10 buildings. (NCC Volume One, F2D2 and F2P2; NCC Volume Two; ABCB Housing Provisions 10.2)
2. Standards referenced: Waterproofing must comply with AS 3740 (Waterproofing of domestic wet areas) for floors and walls in wet areas and, where external waterproofing or roof terraces/balconies are involved, AS 4654 Parts 1 and 2 (Waterproofing membranes for external above-ground use) as referenced in NCC Volume Two H2D8. (NCC Volume One F2D2; NCC Volume Two H2D8)
3. Minimum wall waterproofing height in showers: For shower areas with a hob, step-down or level threshold, walls must be waterproof to a height of not less than 1800 mm above the floor substrate. Wall junctions and joints within the shower must be waterproof at least 40 mm either side of the junction. The shower floor must be waterproof, including the hob or step. (ABCB Housing Provisions 10.2.2; NCC Volume Two Part 10.2 Wet area waterproofing)
4. Shower bases (preformed): A preformed shower base must also meet wall waterproofing heights and junction requirements, except the requirement for the floor substrate waterproofing of a site-formed base is not applicable. (ABCB Housing Provisions 10.2.2)
5. Vessel proximity to walls: Where a bath or similar vessel is within 75 mm of a wall, walls must be water resistant to a height of not less than 150 mm above the vessel for the extent of that vessel; tap/spout penetrations and wall junctions must be waterproof. (NCC Volume One S26C5)
6. Handheld bidet spray (WC): For WCs with a handheld bidet spray, walls within a 1500 mm radius of the connection must be waterproof to a height of not less than 150 mm above the floor substrate, and water resistant to 1200 mm above finished floor level; wall/floor junctions and penetrations within that radius must be waterproof. (NCC Volume One S26C5(3))
7. Wall/floor junctions and penetrations: Where floors and walls are required to be waterproof or water resistant, all wall/floor junctions and penetrations (plumbing, taps, mixers, wastes) must be appropriately sealed and waterproofed. (NCC Volume One F2P2; F2D2; ABCB Housing Provisions 10.2)
8. Laundries and WCs: Laundries and WCs (other than those with bidet sprays) require a water resistant floor, waterproof wall/floor junctions and waterproof penetrations where those surfaces are required to be waterproof. (NCC Volume One S26C5)
9. Floor wastes: Where a floor waste is required by the NCC, the bathroom/laundry must have a waterproof floor, waterproof wall/floor junctions and waterproof penetrations through the floor. (NCC Volume One S26C6)
10. Deemed-to-Satisfy vs Performance Solutions: For Class 2 and 3 buildings (and Class 4 parts) F2D2(1) requires building elements in wet areas to be waterproof or water resistant in accordance with Specification 26 and to comply with AS 3740. Where a Performance Solution is proposed, it must meet the Performance Requirements via A2G2/A2G4. (NCC Volume One F2D2)
11. Materials and system design: External or podium waterproofing must reference AS 4654.1 and AS 4654.2 for materials and installation. Internal wet-area membranes and substrate prep should follow AS 3740. (NCC Volume Two H2D8; ABCB Housing Provisions 10.2)
12. Measurement units and thresholds: Heights are given in mm (e.g., 1800 mm, 150 mm, 1200 mm, 1500 mm radius); proximity thresholds in mm (e.g., 75 mm); these are explicit in ABCB Housing Provisions and NCC clauses noted above.

Residential vs Commercial

1. Residential (Class 1 and 10, plus housing parts of Class 2/3 where Housing Provisions apply): The ABCB Housing Provisions (Part 10.2) give detailed Deemed-to-Satisfy wet-area waterproofing requirements-e.g., 1800 mm wall waterproofing height for showers, 40 mm junction waterproofing extent, and other prescriptive measures intended for domestic bathrooms and laundries. Compliance with AS 3740 is mandatory where specified. (ABCB Housing Provisions 10.2; AS 3740)
2. Commercial and multi-residential (Class 2 to 9): NCC Volume One F2 series sets Performance Requirements that building elements in wet areas must be protected from water penetration. For Class 2 and 3 buildings and Class 4 parts, F2D2 requires compliance with AS 3740 and Specification 26. In some commercial settings (Class 5-9), additional durability, higher traffic or chemical exposure considerations may require more robust membranes, alternative details or specialist systems referenced or beyond AS 3740. External wet areas, balconies and terraces must reference AS 4654. (NCC Volume One F2D2; H2D8)

Exceptions and Exemptions

1. Performance Solutions: Where a Deemed-to-Satisfy solution cannot reasonably be applied, a Performance Solution may be adopted, provided it demonstrates equivalent safety and performance under A2G2/A2G4 processes in the NCC. This can allow alternate membrane systems or detailing when evidence and testing justify the solution. (NCC Volume One A2G2/A2G4)
2. Preformed shower bases: A preformed shower base may be used but must still meet wall waterproofing and junction requirements; the requirement that the floor substrate be waterproof (site-formed base) is not applicable to preformed bases. (ABCB Housing Provisions 10.2.2)
3. Specific product/system approvals: Proprietary membranes or systems tested and certified to relevant Standards may be accepted in lieu of other prescriptive details when supported by manufacturer instructions, test evidence and product warranties as part of a Performance Solution or accepted Deemed-to-Satisfy solution per NCC procedures.

State and Territory Variations

1. NCC state schedules: Each state and territory may include a schedule in the NCC that modifies or adds requirements. Users must check the relevant state schedule in NCC 2022 Volume One (Schedules 4-12) for local amendments. For example, some jurisdictions have amplified requirements for balconies, waterproofing inspections or certification. (NCC Volume One - State schedules reference)
2. Local council and plumbing regulations: States may have separate plumbing codes or local regulations that affect waterproofing and drainage (for example, Queensland and New South Wales have specific building authority controls and inspection regimes). Always verify against your state schedule and local council requirements. (NCC Volume One - check state schedules)
3. Housing Provisions applicability: The ABCB Housing Provisions are tailored for Class 1 and 10 and inform many domestic requirements, but where state variations exist they will be listed in the applicable schedule-consult the NCC state schedule and local authority. (ABCB Housing Provisions Part 10.2)

Practical Compliance Tips

1. Follow AS 3740 in full: Use AS 3740 as the primary prescriptive guide for domestic wet-area membrane selection, substrate preparation, membrane application and protection; many NCC Deemed-to-Satisfy clauses require compliance with AS 3740.
2. Observe height and extent dimensions exactly: Install wall waterproofing at showers to 1800 mm above the floor substrate and ensure 40 mm waterproofing beyond internal joints - inaccurate heights are a common noncompliance at inspections. (ABCB Housing Provisions 10.2.2)
3. Seal penetrations and junctions first: Treat all pipe penetrations, mixer fixings, spout penetrations and wall/floor junctions with appropriate waterproofing collars, bonded reinforcement and sealants before tiling or lining. (NCC Volume One F2D2; AS 3740)
4. Use compatible systems and manufacturer instructions: Membrane, adhesive and tile systems must be compatible and installed strictly to the manufacturer’s instructions and tested systems in accordance with AS 3740 and, for external areas, AS 4654. Keep product data and installation records for certification. (NCC Volume Two H2D8; AS 4654)
5. Inspect under-lining before finishes: Arrange certifier or inspector checks of the membrane and junctions before covering (prior to tiling or linings). Photographic records and sign-off reduce disputes at handover.
6. Consider fall and floor waste location: Ensure adequate fall to the floor waste and that floors with required wastes have fully waterproof floors and wall/floor junctions as specified by the NCC. Incorrect falls or misplaced wastes are frequent retrofit failures. (NCC Volume One S26C6)
7. Account for special fittings: If a handheld bidet spray is fitted, waterproof walls and junctions within a 1500 mm radius to the heights specified to prevent spray-related water damage. (NCC Volume One S26C5(3))

References cited inline: NCC 2022 Volume One - F2D2, F2P1, S26C5, S26C6; NCC 2022 Volume Two - H2D8; ABCB Housing Provisions 10.2 (Wet area waterproofing); AS 3740 (Waterproofing of domestic wet areas); AS 4654.1 and AS 4654.2 (external waterproofing membranes).

Note: State or territory schedules in NCC 2022 Volume One may modify these provisions; always verify requirements against the relevant state schedule and consult a registered building certifier for complex or borderline cases.