To grade, or not to grade

Image of shower drain

Have you ever wondered whether the floor surrounding a floor waste is required by the NCC to be graded to that floor waste in all circumstances?

While not likely to be a dinner party conversation topic, this question has been occupying the minds of some NCC users. So earlier this year at a joint meeting of the ABCB’s Building Codes Committee and Plumbing Code Committee considered it.

When are floor wastes required?

Floor wastes are only required by the Deemed-to-Satisfy Provisions of the NCCin prescribed situations:

  • In a shower area, as part of the AS 3740 wet area waterproofing requirements (Volume One F1.7 & Volume Two
  • In a room containing a urinal (Volume One F1.7 & AS 3500.2 through Volume Three Part C2).
  • In a Class 2, 3 or Class 4 part of a building, where a bathroom or laundry is located above a sole occupancy unit or public space (Volume One F1.11).

In the above situations, the floor is required by the NCC to be graded to the floor waste to prevent water overflow from penetrating to other occupancies or public spaces in the same building.

A floor waste will also form part of a floor waste gully in circumstances where that gully may be required by the PCA Deemed-to-Satisfy Provisions (AS 3500.2 through Volume Three Part C2). As the purpose of providing a floor waste gully in these circumstances is to ensure the proper functioning of the sanitary drainage system rather than preventing overflow from penetrating other occupancies or spaces, the floor is not required by the NCC to be graded to these floor wastes.

Floor wastes not required by the NCC

Floor wastes may also be installed even though they are not required by the NCC, for example, outside the shower area in a residential bathroom. As there is no requirement in the NCC to control overflows in these circumstances, it follows that there is also no requirement in the NCC to drain the floor to these floor wastes.

Of course, even though the NCC may not require floors to be graded to some floor wastes, there is nothing that prevents this being done if desired, but in those circumstances it should be understood it is not a regulated requirement under the NCC.


[1] The national BCA provisions for waterproofing of wet areas are subject to variation in South Australia by virtue of SA 3 (Volume Two) and SA F1.11 (Volume One).

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