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Waterproofing Behind Wet Area Tiles

Effective waterproofing is vital for tiled showers & splashbacks & is highly important to keep bathrooms, laundries, & kitchens generally in good condition.  Too often, poor waterproofing results in failures, leaks & costly repairs.  Even if you don’t do the job yourself, it is still important to know how far waterproofing should go.


Water escaping from a shower & from around a bath, basin or the like can remain unnoticed for long periods & cause serious damage.  Properly detailed & installed waterproofing is essential behind tiled surfaces with cement based grouts because tiling is not inherently waterproof, & failure of tiled surfaces is a common problem in New Zealand.


Building Code clause E3 Internal Moisture requires buildings to be constructed to avoid fungal growth on linings, water overflowing to adjoining units & moisture damage to building elements.  Acceptable Solution E3/AS1 does not specifically define a wet area, but uses the terms ‘subject to watersplash’ & ‘showers’ when defining wet area requirements.


Considering the risk of water damage, there are two types of areas:

  • Those subject to frequent & heavy wetting, such as showers & open shower surrounds, & splash areas around baths & basins.
  • Those subject to regular intermittent wetting, such as floors in bathrooms, kitchens & laundries & the walls behind baths, basins & tubs. Tiled entries also fall into this category when people enter the house during heavy rain.
  • For both these types of areas, BRANZ recommends tiles be installed over a waterproofing system except where the substrate is steel-trowelled or polished concrete.  (In E3/AS1, a waterproofing membrane is required for tiled shower enclosures where tiles are laid over an absorbent substrate such as fibre-cement or water-resistant plasterboard).


As good practice for tile finishes, BRANZ recommends the installation of a waterproofing membrane:

  • in bathrooms, kitchens & laundries, to all absorbent floor substrates.
  • in an open shower, to all wall tiles within 1.5 m of a fixed showerhead plus the length of the flexible shower hose – waterproofing should go to the ceiling where the showerhead is removable.
  • in an open shower over a bath, to all wall tiles as above or the length of the bath plus 300 mm for a fixed showerhead.
  • in an enclosed shower, to all floor & wall tiles – waterproofing should go to the ceiling where a removable showerhead is installed.
  • for baths, waterproofing should extend at least 300 mm above & beyond the top of the side & ends of the bath.
  • for basins, waterproofing should go at least 150 mm above & past the hand basin.


For more information, see BRANZ Bulletin 518 Wet area tile waterproofing.

Article source – BRANZ Builder’s Mate Publication, Issue 60.