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.

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

For bathroom floors, the recommended minimum fall to the waste shall be 1:100 (10mm per 1m). For shower areas with a vertical separation between the shower area and the wet area, such as a shower screen, hob, set-down or water stop, the fall to the waste shall be 1:100.

For all other shower areas the recommended fall shall be a minimum of 1:80 (12.5mm over 1m). Where falls flatter than 1:100 are proposed, the effectiveness of the floor drainage should be confirmed to ensure that water does not remain on the finished floor in a manner that can adversely affect the health and amenity of the building occupants or deteriorate building elements. In other words, the water must drain away, with the exception of residual water.
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In all cases, tiles may require diagonal cutting in the area around the waste to achieve the required falls, sufficient drainage and to ensure lipping is kept within the guidelines of AS 3958.1.

Credit: Australian Tile Council