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
  • Particleboard
  • Plywood
  • Compressed sheet (fibre-cement)
  • Vinyl
  • Terrazzo, concrete and cement plaster
  • Ceramic and stone tiles
  • Timber treatment
  • Waterproof membrane
  • Substrate preparation
  • Cork tiles
  • Sheet rubber
  • Linoleum

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:

  • timber and timber-based materials, such as timber strip and overlay flooring, particleboard or plywood, if they are sealed with a waterproof applied coating
  • compressed sheet (fibre-cement) used as a substrate
  • waterproof sheet material such as vinyl
  • terrazzo, concrete or cement plaster with steel trowel or polished finish
  • ceramic and stone tiles with 6% maximum absorption (joints must be waterproof and bedding material specified as suitable for wet area use)
  • cork tile or sheet with a waterproof coating and sealed joints.

Floor finishes that may be suitable for wet areas but are not listed in E3/AS1 (so must be consented as an Alternative Solution) include:

  • synthetic or natural rubber sheet with welded seams
  • linoleum (not suitable for use in showers)
  • epoxy-based coating systems
  • polyester resins with mineral aggregate
  • polyurethane-based systems.

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.

Particleboard

Although a commonly used flooring material, particleboard is very easily damaged by moisture. Its use as a wet area floor substrate is permitted under E3/AS1, but it must have an applied waterproof coating. Where it is considered the coating may be not well maintained (e.g. it is not easily accessible and therefore maintenance unlikely to be carried out), an alternative floor substrate should be selected.

Plywood

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

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.

 
Wall/floor detail

Coved vinyl

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.
 
Tile flooring

Coved tile flooring

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.

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

Bath – minimum extent of waterproof membrane under tiled surfaces

 
Tiling

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.

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.

Cork tiles

Cork tiles are permitted in splash zones under E3/AS1 when finished with a waterproof applied coating, but are not suitable where there is continual wetting (e.g. showers). They must be laid over a rigid substrate and, if installed under floor-mounted fittings such as vanity units, baths and shower trays, should be finished with a continuous, impervious coating.

Sheet rubber

Sheet rubber is an impervious material and generally unaffected by water. Manufacturers’ 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.

Linoleum

Linoleum is a resilient, non-toxic flooring material that contains wood in the form of fine sawdust. It is not susceptible to damage from oils or organic solvents (making it suitable for use in kitchens), but will deteriorate if subjected to continual wetting, particularly if water gets underneath it. It is therefore not recommended in wet areas such as showers but may be used in splash zones. It should be coved up walls and front panels and toe spaces of built-in fittings. Unless it has a textured finish, it may be slippery when wet.

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

www.dbh.govt.nz

BRANZ Good Practice Guide: Tiling

 

Updated: 16 April 2014