Gradient falls in wet area floors

Drainage

​The primary consideration regarding a wet area floor is to ensure that the water drains adequately. The trend to large format tiles brings the added complication of obtaining a floor fall to a single waste outlet and to avoid tile lippage in the process. AS 3740 – 2010 - Waterproofing of domestic wet areas, is a ‘deemed to comply’ standard to the Building Code of Australia.

​The primary consideration of this standard, for falls in floor finishes, is to ensure water does not remain on the finished floor in a manner that can adversely affect the health or amenity of the occupants or deteriorate building elements.

Control of water in shower areas is critical. There are two types of showers defined in AS3740, an enclosed shower where water spread is controlled within the shower area. An unenclosed shower where water is not confined within the screened area, residual water is controlled by installing a water-stop that protrudes above the floor level under the base of the screen. Water in unenclosed showers is also controlled by laying tiles to appropriate falls.

Residual Water

​AS 3740 – 2010 also states that water should not pond on the floor, with the exception of residual water remaining due to surface tension. In regards to residual water, it should be noted that no amount of slope would see all the water runoff. Consider the angle of a car windscreen, water still beads there, it even beads on vertical window glass, so complete and immediate run off is unrealistic.

Puddle flanges must be flush with the mebrane or recessed without any lippage, preventing water or moisture from draining. 

Flooding

The scope of AS 3740 2010 states that ‘The Standard does not cover situations where flooding of the wet areas occurs through overflowing of vessels and showers or plumbing failures’. As such flooding of floors cannot be considered when assessing the effectiveness of the drainage of floors.

Factors affecting falls

The following factors can affect fall ratios:

• Finished height requirements at doorways;
• Height of fixtures or fittings;
• Dimensions of tiles used;
• Area of the floor to be drained; and
• Requirements of persons with disabilities.

Floor falls

The Housing Provisions have changed to require that surface finishes grade to every drain waste (that is any hole in the floor) in a wet area.

Where a floor waste is installed:

(a) the minimum continuous fall of a floor plane to the waste must be 1:80; and
(b) the maximum continuous fall of a floor plane to the waste must be 1:50. (Part 10.2.12 ABCB Housing Provisions)
This applies regardless of whether the floor waste was required to be installed as a requirement of NCC 2022, or if the floor waste was installed voluntarily.

Performance Requirement H4D2 for Wet Areas allows compliance through AS 3740 or Part 10.2 of the ABCB Housing Provisions. However, even if you choose AS 3740 as a pathway you will still have to meet the requirements of 10.2.1 to 10.2.6 and 10.2.12 of the ABCB Housing Provisions.

The old interpretation that a floor waste gully fixture trap (usually centre of the wet area floor) is not a drain waste, is now obsolete because of the new wording.