Wet Areas

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

Wet area design

Wet areas should be designed to be safe, accessible, comfortable and convenient for users – and to be durable and meet all relevant Code requirements.

On this page:

  • Health and safety
  • Lighting
  • Comfort
  • Preventing fungal growth
  • Preventing damage to structure and finishes.

Wet areas must be designed to meet statutory requirements, including the requirements of Building Code clause E3 Internal Moisture, which aims to safeguard building users against illness, injury and loss of amenity, and to protect the rest of the building from water damage.

Key sustainable building considerations affecting wet areas include efficient use of  Energy and Water, and assuring the performance and durability of the structure and finishes by preventing water damage.

Health and safety

Of the many potential safety problems with wet areas, the most obvious is the risk of slips and falls if floors (or other surfaces such as bathtubs or shower trays) become slippery when wet. This is a risk especially for people 65 and over (one in six New Zealanders):

  • ACC said in 2021 that each year it accepts around 155,000 claims for falls and fracture-related injuries among New Zealanders aged 65 years or over.
  • Less than half of those who survive a hip fracture will walk unaided again.
  • Around 10-20% of people who sustain a hip fracture will be admitted to a care home in the year after fracture.

The potential harm from a fall is heightened if there are sharp edges in the area that might injure a person who falls, or if there is glass that might shatter if someone falls against it. To reduce these risks:

  • select a textured floor finish or floor finish with a slip resistance coefficient of 0.4 maximum when wet – Table 2 of D1/AS1 gives details of flooring materials and finishes with acceptable slip resistance. (Also see BRANZ Bulletin BU 626 Slip resistance of floors)
  • avoid using a highly reflective floor finish
  • select a shower and/or bath with a textured/slip-resistant surface and a level base
  • install grab rails in and beside the shower cubicle and bath area
  • avoid sharp edges that may injure people if they fall
  • specify grade A safety glass in accordance with NZS 4223.3:2016 Glazing in buildings - Part 3: Human impact safety requirements. This Standard requires grade A safety glass in framed and unframed shower doors, screens and bath enclosures, and all glazing less than 2.0 m from the floor.

If a person falls across the door to a wet area, this may prevent others from getting in to provide help. To reduce this risk, specify a bathroom lockset that allows emergency access, and if possible install an outward opening door or a door with lift-off hinges.

Other potential safety risks include:

  • scalding, if the temperature at hot water outlet is too high – Building Code clause G12 Water supplies requires that Hot water supply be designed and installed to protect users from scalding; see Hot water supply for details
  • risk of electrical faults from incorrectly wired or used appliances – to minimise this risk: ensure that bathroom heaters and heated towel rails are permanently wired; locate power outlets (for shaving) a safe distance from the bath, basin and shower; and in kitchens and laundries specify an adequate number of power outlets so there is no need for messy cords and multi-boxes.


Wet areas must be adequately lit, both for safety reasons and for the convenience of building users. Lighting must comply with the requirements of Building Code clauses G7 Natural light and G8 Artificial light.

For natural lighting, G7/VM1 provides a method for assessing illumination and G7/AS1 specifies rules for obtaining satisfactory lighting levels; however, these don’t apply to any bathroom, laundry, toilet ‘or other space of a specialized nature occupied neither frequently nor for extended periods’. Acceptable Solution G8/AS1 provides a means of compliance for artificial lighting.

Wet area light fittings should be located so they:

  • illuminate work surfaces without creating shadows (kitchen bench, vanity top)
  • provide light in front of mirrors to illuminate the user (bathrooms).

Light fittings should be durable in a damp environment and not allow moist air to pass into concealed spaces (such as a skillion floor or inter-floor spaces).


Wet areas, particularly bathrooms, should not be uncomfortable or unpleasant spaces to use. Conditions that that will compromise occupant comfort include:

Preventing fungal growth

Condensation, which provides the environment for the fungal growth, can be minimised by maintaining an appropriate balance between temperature and ventilation. Insulation helps further by maintaining the internal temperature at a suitable level. See Managing temperature and condensation for details. G4/AS1 requires extractor fans to ventilate bathrooms and kitchens. The extractor fans must exhaust the air to the outside.

Preventing damage to structure and finishes

Water damage can cause:

  • rot to timber wall and floor framing
  • rust in steel fixings
  • deterioration or disintegration of wall linings, flooring (especially particleboard) and cabinetry (especially MDF)
  • paint to peel
  • water to pool in the subfloor.

Water damage may be caused by design issues such as inappropriate material selection, or poor design of junctions and wall penetrations.

Damage may also be caused by faults in installation or use, such as:

  • poor construction of plumbing, particularly at junctions and penetrations
  • failure of waterproofing membranes
  • overflowing or spillage from baths, showers and other fixtures
  • no floor drain
  • leaks
  • blockages in WC pans and water traps.

To reduce the risks of water damage, specify suitable substrates, impervious finishes and/or waterproofing (see Wet area flooring and floor finishes, Wet area wall structure, and Wet area wall and ceiling linings and finishes).

Also take steps to manage water overflow and splashing.

As noted above, all wet areas must comply with Buildin/equires that water overflow is disposed of appropriately and that surfaces are impervious and easy to clean.


Updated: 26 August 2022