Floor wastes in bathrooms when are they required

Two of the most common questions HIA receives on waterproofing are ‘when do you need to install a floor waste?’ and ‘does it require fall in the floor to the waste?’ There is much anecdotal evidence out there in relation to this, but what are the facts?

There are two primary documents in relation to wet areas construction:

• National Construction Code (NCC)
• AS 3740 – Waterproofing of domestic wet areas.

Both contain information on materials and methods required in relation to waterproofing bathrooms and wet areas such as WCs and laundries.

The NCC has two parts: Volume 1 for Class 2 - 9 buildings and Volume 2 ‘Housing Provisions’ for Class 1 and 10 buildings.

NCC Volume 2 references or ‘calls up’ AS 3740 as an NCC primary referenced document. AS 3740 contains the detailed waterproofing of wet area provisions for Class 1 buildings (houses). NCC Volume 1 also applies AS 3740 to certain classes of commercial buildings.

There are several things to consider in determining if a floor waste needs to be installed.

You also need to consider the requirements and options available for sanitary drainage under the Plumbing Code of Australia (PCA) and AS/NZS 3500.2.

Class 2, 3 or Class 4 part of a building 

For apartment buildings (Class 2 buildings), hotels, motels and boarding houses (Class 3 buildings), and residential parts of commercial buildings (Class 4 parts of a buildings), NCC Volume One requires a floor waste be installed in bathrooms and laundries if a bathroom or laundry is situated at any level above a sole-occupancy unit or a public space. A public space in a building would include areas such as public foyers and reception areas.

In these circumstances the floor to the room is required to be waterproof and the floor graded to the floor waste to permit drainage of the water. The required fall of the floor, the waterproofing requirements of the floor and the installation details of the floor waste are specified in the NCC.

The intent of this provision is to provide protection from flooding to an adjoining separate unit or a public area.

NCC Volume One Also requires installation of a floor waste in any room containing a urinal in a Class 2-9 building.

Class 1 buildings 

Class 1 buildings ‘require’ a floor waste be provided within the shower area. This is indicated in both the NCC and AS 3740.

The NCC defines a shower area as the area affected by water from a shower, including a shower over a bath and for a shower area that is - 

• Enclosed - the area enclosed by walls or screens including hinged or sliding doors that contain the spread of water to within that space; or
• Unenclosed - the area where, under normal use, water from the shower hose is not contained within the shower area.

The required fall of the floor, the waterproofing requirements of the floor and the installation of the floor waste are specified in the NCC.

For the area outside of the shower area an additional floor waste is not ‘required’ to be provided, nor is one ‘required’ to be provided in other wet areas such as in a laundry or in a WC. For an unenclosed shower, the floor outside the shower can be graded to the shower waste.

For a shower over a bath that is ‘unenclosed’ the NCC and AS 3740 ‘requires’ an additional floor waste be provided (see Figure 1). In this case, 'unenclosed' means the shower over bath is not provided with a minimum 900 mm wide screen for the open side of the bath that contains the water within the bath.

It should be noted that these requirements are the minimum requirements only. A designer or builder may choose to install an additional floor waste (i.e. in addition to the one in the shower area) or provide one to the floor in a laundry or WC voluntarily. In this case the floor must fall to the waste.

Plumbing and drainage requirements for bathrooms and wet areas

Plumbing & drainage requirements for all classes of buildings are set out in Plumbing Code of Australia (PCA). In turn the PCA references the AS/NZS 3500 suite of standards for the detailed technical requirements for plumbing & drainage installations.

Specifically, AS/NZS 3500.2 sets out the sanitary plumbing and drainage requirements and these requirements are replicated in AS 3500.5 (Housing Installations).

AS/NZS 3500.2 contains several provisions relating to the installation of floor waste gullies in bathrooms as part of the installation of certain waste fixtures such as baths, basins, showers, laundry tubs etc.

However, it should be noted that AS/NZS 3500.2 does not prescribe that a floor waste gully must be installed, rather it is listed as an option as part of the installation of the waste fixture(s). For example a bidet can be installed with a trap and waste pipe or with an untrapped waste pipe to a floor waste gully.

Floor wastes in shower areas

An individual shower must be fitted with a DN80 (minimum) grate or channel grate that discharges via:

• An untrapped DN40 waste pipe to a floor waste gully; or
• A trap and wasste pipe no smaller than DN40

Clause 13.3.6 of AS/NZS 3500.2 states if a fixture trap is not accessible the grate shall be removable. This applies to the shower trap.

Drainage options for bathtubs

For bath installations, AS/NZS 3500.2 contains a few options:

• The bath discharges by an untrapped DN40 waste pipe to a floor waste gully, or
• The bath is provided with an accessible trap and waste pipe no smaller than DN40.

Where a floor waste gully is used:

• It must be within the same room as the fixture served.
• It must be within 1200mm of the fixture outlet (2500mm if your plumbing design allows it to be a submerged inlet gully).
• The floor waste gully must have minimum DN80 riser, a removable grate, and achieve the minimum height from water seal to floor level per AS/NZS 3500.2 Table 4.5.7.7.
• The floor waste gully may be integrated with the shower waste (Figure 2).
• The floor must fall to the floor waste gully at a grade between 1:80 and 1:50

Drainage via an accessible trap:

• Accessible means capable of being reached, but may first require removal of an access panel, cover, door or similar obstruction.
• If you are required to cut or break a wall, ceiling, tiled or waterproof element, it is not accessible.

It is relatively simple to achieve an accessible trap in a house with a suspended floor, or in an upstairs bathroom. This can be via a snap vent or other access panel.

In a slab-on-ground, designing an accessible trap under a bath is more difficult. An accessible trap may still be possible via:

• A bath with enough room underneath to fit a DN40 trap and waste pipe. This would typically require at least 180mm clearance from the floor level.
• Clawfoot baths may have enough room underneath for a DN40 trap.
• Freestanding baths on plinths or pedestals could be another option, if the plinth or pedestal has an access port that is appropriately waterproofed, or removal of the bath is readily achievable by non-destructive means.
• It may also be possible to access beneath a trapped bath via a port in a wall to an adjoining room (e.g. hidden in a wardrobe).

Falls to floor wastes

HIA is aware that there are some differing views as to whether a floor is required to be graded to the floor waste:

• where required by the NCC; or
• an additional floor waste is provided voluntarily i.e. it is not required by the regulations to be provided; or
• a floor waste gully is installed as part of a plumbing and drainage installation of a waste fixture(s).

NCC 2022 has been amended to more explicitly require that a floor be graded to the floor waste and meet other compliance requirements where a floor waste is installed. The requirement to provide a continuous fall in the plane of the floor is prescribed in the NCC. ABCB Housing Provision Standard Clause 10.2.12 and F2D4 of NCC Volume One.

The NCC now specifies that where a floor waste is installed, be it to meet a mandatory requirement of NCC or installed voluntarily, that the floor must fall to that floor waste meeting prescribed grades that being a maximum fall of 1:50 and minimum fall 1:80.

Performance Solutions and State and Territory variations

If you wish to use an alternative arrangement to either achieve the drainage requirements of the PCA or the fall in the floor under the BCA, it is possible to develop a Performance Solution. These will need to go through approval process required in your jurisdiction.

F2V1 of NCC Volume One also allows the BCA's overflow requirements to be achieved by verification that the capacity of installed overflow devices exceeds the flow rate of the source, under a simple Performance Solution for bathrooms, laundries and the like Class 2,3 or 4 parts.

As some states maintain variations to the NCC which alter options for compliance in some circumstances, it is also important to check with your local authority or administration for any specific State or Territory provisions in relation to the installation of floor wastes that may override the NCC or Australian Standards provisions.

To find out more, contact HIA's Building Services team.

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