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 flooring and floor finishes

A wide range of wet area flooring and floor finishes is available, each with pros and cons

On this page:

  • Code requirements
  • Timber strip and overlay flooring
  • Reconstituted wood boards
  • Plywood
  • Compressed sheet (fibre-cement)
  • Vinyl
  • Terrazzo, concrete and cement plaster
  • Ceramic and stone tiles
  • Timber treatment
  • Waterproof membrane
  • Substrate preparation
  • Sheet rubber

Code requirements

In accordance with NZBC clause E3 Internal moisture, finished floors within wet areas must be impervious, maintain the integrity of the system and use materials and finishes suitable for wet areas.

Flooring materials that are not impervious may provide the substrate for an impervious floor finish while, with appropriate treatment, other flooring materials provide the floor finish.

Acceptable Solution E3/AS1 lists suitable finishes for wet areas as:

  • waterproof sheet material (such as PVC) with sealed joints and sealed or coved at edges  
  • ceramic or stone tiles with 6% maximum water absorption and waterproof grouted joints  
  • a slab-on-grade concrete slab floor with a steel trowel or polished finish.

    E3/AS1 makes the comment that other floor finishes may also satisfy performance requirements, but they are outside the scope of the Acceptable Solution. This means that they must be consented as an Alternative Solution. 

    See the Quick reference guide for wet area floor finishes. While the main criteria for selecting a wet area floor finish must be its performance and durability, also consider the sustainability of the materials used. See Material use for more detail.

    Timber strip and overlay flooring

    Timber is susceptible to moisture damage so it must have an applied waterproof coating when used as wet area flooring. Normal movement in the boards of timber strip flooring and overlay flooring may lead to the joints between the boards opening up and cracking the applied finish, which can allow water to enter the timber. Therefore, BRANZ does not recommend timber strip or overlay flooring in areas subject to water splash or wet cleaning.

    Vinyl composite strip flooring

    An alternative to timber strip flooring with a broadly similar appearance is vinyl strip flooring. Planks can be made of materials such as recycled wood and bamboo dust in virgin PVC. The planks are waterproof and suitable for wet area flooring.

    Reconstituted wood boards (particleboard, strand boards)

    Although a commonly-used flooring material, untreated particleboard can be easily damaged by moisture. When used in wet areas it should be treated to H3.1. In water-splash areas (around baths and vanities) it must be protected by waterproof sheet material with sealed joints, or a waterproof membrane. In shower areas it must be protected with a waterproof membrane system specified for use with timber panel flooring. Installing a floor waste is recommended.


    Plywood provides a very rigid substrate for other finishes but is not usually used as finished flooring. As it can be treated to H3, giving it good resilience to water damage, it may be used in situations where access and maintenance of a particleboard floor is not practical. When used as the finished flooring, it must have an applied waterproof coating. Note that, because of the solvents used in the treatment, LOSP treated material is not suitable for use with applied waterproofing membranes used under tiles and a number of other impervious finishes – use CCA-treated plywood instead.

    Compressed sheet (fibre-cement)

    Compressed sheet is not used as finished flooring, but it provides a stable substrate for floor finishes. Although less susceptible to moisture damage than timber or timber-based products, it is not an impervious material.


    Vinyl is an impervious, water-resistant material that is ideal as a wet area floor finish. It is also suitable for use in showers. It is available in sheet and tile form but only sheet vinyl is permitted under E3/AS1. Vinyl must be laid with heat or solvent-welded joints to be fully watertight. It must be laid over a rigid substrate such as concrete, particleboard, plywood or compressed sheet, as cracking may occur if there is substrate movement, and it should be coved up walls and the front panels and toe spaces of built-in fittings. A profiled surface should be selected, as it can be slippery when wet.

    Terrazzo, concrete and cement plaster

    Wet areas finished in terrazzo, concrete or cement plaster require a steel trowelled surface finish or a surface that has been ground and polished to be impervious. These floor finishes may require surface profiling to give slip resistance to the floor.

    Ceramic and stone tiles

    Ceramic and stone tiles are popular finishes for wet areas and for showers in particular. They must have 6% maximum water absorption, and glazed tiles should have glazed edges. A tiled finish requires:

    • a firm, stable, rigid substrate such as concrete, plywood or fibre-cement sheet
    • a waterproof membrane laid underneath the tiles in accordance with AS/NZS 4858:2004 Wet area membranes – a membrane is required behind all tiles within the shower and recommended for all bathroom laundry and kitchen tiled floors, as cement-based grout joints are not waterproof
    • a fall of 1:50 to the waste outlet in showers
    • flexible (mould inhibiting sealant) movement joints at the floor/wall and wall/wall junctions.

    Although tiles may have an impervious finish, if they are not installed correctly, the joints and substrate may not be waterproof.

    See Good Practice Guide: Tiling for more information.

    Timber treatment

    Treatment levels for timber and timber-based materials used under tiles in wet areas where the waterproofing membrane cannot easily be inspected or maintained should be:

    • H1.2 for timber floor joists and wall framing around showers
    • H3 (CCA treated) for plywood.

    Waterproof membrane

    Substrates must be protected by:

    • a waterproof applied coating such as liquid applied acrylic or polymer coating, glass-fibre reinforced resin, water- or solvent-borne polyurethane, cementitious two-part coating, or peel and stick modified asphalt/bitumen sheet membrane
    • an impervious finish such as vinyl sheet.

    A new Acceptable Solution for internal wet area membranes was introduced on 5 November 2020. The Acceptable Solution references the membrane manufacturers’ Code of Practice for Internal Wet-area Membrane Systems with a few amendments. Membranes installed in accordance with sections 1–4 of the Code of Practice (as modified by the Acceptable Solution) will comply with Building Code clauses E3.3.2 – E3.3.6.

    BRANZ recommends that waterproofing membranes should be:

    • continuous under floor-mounted vanity units, baths and shower trays and extend at least 150 mm up the adjoining walls when walls are not waterproofed
    • under all tiling in areas subject to regular water splash
    • sealed around penetrations so there is no path for water to migrate to adjacent spaces.
    Enclosed tiled shower

    Enclosed tiled shower – minimum extent of waterproof membrane

    Unenclosed tiled shower 
    Unenclosed tiled shower

    Unenclosed tiled shower – minimum extent of waterproof membrane

    Bath with shower over 
    Bath with shower over

    Bath with shower over – minimum extent of waterproof membrane under tiled surfaces


    Bath – minimum extent of waterproof membrane under tiled surfaces


    Tiling and recommended waterproof membrane to vanity units

    Substrate preparation

    Before placing the membrane, the substrate must be clean and have a moisture content of:

    • concrete or mortar - 75% or less RH
    • plywood - 20% or less moisture content.

    Waterproof membranes must be installed according to manufacturers’ instructions. Membrane manufacturers often require their systems to be installed/applied by specialist or licensed applicators.

    Waterproof membrane failures occur because there is:

    • a lack of curing
    • insufficient thickness of the membrane (liquid)
    • incorrect membrane selected
    • dilution of liquid-applied membrane
    • no reinforcing
    • poor installation
    • damage from subtrades
    • incompatible adhesive
    • underfloor heating that is too hot or incompatible with the membrane
    • water migration around the edge of the membrane.

    Sheet rubber

    Sheet rubber is an impervious material and generally u/acturers’ recommendations should be checked for suitability of use. It must be laid over a rigid substrate. Joints must be heat-welded to be fully impervious, and it should be coved up walls and front panels and toe spaces of built-in fittings. It should be continuous if laid under floor-mounted fittings such as vanity units, baths and shower trays.

    Epoxy and resin-based finishes

    Although not common in domestic wet areas, epoxy and resin-based waterproof coatings are an option to provide an impervious surface. These finishes can be applied to most substrates. They should be applied before floor-mounted fittings such as vanity units, baths and shower trays are installed.

    More information

    BRANZ Good Practice Guide: Tiling


    Updated: 09 November 2020