Wet Areas

Poor wet area design or installation can compromise safety, comfort and convenience for building users, and lead to significant structural damage.

Statutory requirements

The design and installation of wet areas must comply with NZBC clause E3 Internal moisture.

The objectives of clause E3 are that wet areas must:

  • safeguard against illness, injury and loss of amenity from the accumulation of moisture
  • protect adjacent household units from water damage.

The objectives require that:

  • spaces have adequate thermal resistance, ventilation and space temperature
  • any overflow must be disposed of appropriately
  • surfaces are impervious and easy to clean.

The Acceptable Solution E3/AS1 provides a means of meeting clause E3 Internal moisture requirements.

E3/AS1 contains comparatively little information at the moment, however, so means of compliance with clause E3 will often be through use of Alternative Solutions.

Other Building Code clauses that may be applicable to wet areas are summarised in the following table (see http://www.building.govt.nz/building-code-compliance/).

Clause VM/AS Relevance to wet areas
B1 Structure B1/AS1 Cites NZS 4223.3:2016 Glazing in buildings – Part 3: Human Impact Safety Requirements. This Standard gives minimum requirements for glazing where it could be subject to human impact, aiming to reduce the risk of personal injury.
B2 Durability B2/VM1 Cites evaluation of durability by taking into account:
• in-service history
• laboratory testing
• performance of similar materials.
  B2/AS1 Specifies the durability requirements of building elements based on the difficulty to detect or access problems, or replace them.
C Protection from Fire C/AS1 Part 7: Prevention of fire occurring.
F2 Hazardous building materials F2/AS1 Cites NZS 4223 Part 3 Human impact safety requirements with modifications. Applies to glazed panels and glazing in windows and doors.
G1 Personal hygiene G1/AS1 Sets the numbers of sanitary fixtures to be provided for residential and non-residential buildings. Specifies:
• methods of sanitary towel disposal
• fixture construction and installation
• location of sanitary fixtures
• sanitary fixture requirements for people with disabilities.
G2 Laundering G2/AS1 Specifies laundry requirements for various defined uses.
G4 Ventilation G4/VM1 Specifies methods of:
• measuring ventilation rates
• demonstrating air purity.
  G4/AS1 Sets rules for and limitations on natural ventilation using opening windows. Includes kitchen and bathroom extractor fans as a compliant way to ventilate bathrooms and kitchens.
G5 Interior environment G5/AS1 Specifies methods of providing the heating requirements for habitable spaces, bathrooms and recreation rooms of retirement homes and early childhood centres.
G6 Airborne and impact sound G6/VM1 Specifies the performance requirements for airborne and impact sound transmission between abutting occupancies.
  G6/AS1 Specifies acceptable building element assemblies for minimising sound transmission.
G7 Natural light G7/VM1 Cites NZS 6703:1984 Code of practice for interior lighting design, Appendix A as a method of assessing illumination.
  G7/AS1 Specifies rules for obtaining a satisfactory illuminance level in habitable rooms, but excludes bathroom, laundries and so on, for which there are no special requirements.
G8 Artificial light G8/AS1 To provide a minimum illuminance of 20 lux per square metre of floor area to enable safe movement.
G9 Electricity G9/VM1 Cites AS/NZS 3000, NZECP 34, NZECP 36 and NZECP 54 as methods of verifying compliance.
G9 Electricity G9/AS1 Cites NZECP 51 as an acceptable solution for dwellings.
Sets rules for light switches and socket outlets for use by people with disabilities.
G12 Water supplies G12/VM1 Cites AS/NZS 3500.1 and AS/NZS 3500.4 as a means of compliance.
  G12/AS1 Specifies rules for piped water supply systems.
G13 Foul water G13/VM1 Cites BS EN 12056.2 as a means of compliance.
  G13/AS1 Sets out rules for sanitary plumbing for buildings up to three levels.
G13 Foul water G13/AS3 “Cites AS/NZS 3500.2 (as modified by paragraph 2.0.2 of G13/AS3) as an Acceptable Solution for plumbing and drainage”
H1 Energy efficiency H1/VM1 Specifies methods of determining the insulation requirements using:
• NZS 4218:2009 Thermal insulation – Housing and small building
• building performance index for housing
• NZS 4243.1:2007 Energy efficiency – Large buildings – Building thermal envelope section 4.4
Specifies a method for determining the required minimum R-values for all building envelope components including glazing.

While not cited in Building Code compliance documents, AS 3740-2010 Waterproofing of domestic wet areas is a reference standard for the waterproofing of wet areas.

Any glazing that is within 2 m of the floor in bathrooms and spa rooms must be safety glass, under NZS 4223.3:2016 Glazing in buildings Part 3: Human impact safety requirements.

AS/NZS 4858:2004 Wet area membranes is another key document.

There are also specific legal requirements around wet area ventilation etc. that apply just to rental houses. You can find out more about them in the Healthy homes standards here.


Updated: 8 March 2021