https://www.houzz.com.au/discussions/bathroom-wet-area-back-to-wall-or-built-in-bath-advice-please-dsvw-vd~5591192?n=23

WA might have different rules, but his is OK in NSW

I'm in Perth. To my knowledge this is not correct. If the fall of the tiling is laid correctly and waste installed correctly there is no reason why you can't have a hob less shower. They are every where in WA. Are you in an apartment?

Have looked further into this. Please see the attached information. https://www.commerce.wa.gov.au/sites/default/files/atoms/files/technical_note_overflow_relief_gullies_august_2017_0.pdf
Your plumber may be correct, depending on the site you are building on, with its connections to drainage.

Hi Dreamer and thanks for your reply.

It is something to do with the ORG and the 150mm. We’re told ours doesn’t comply. Seems a landscaper built up the height to allow for a raised garden bed. Now we’d have to remove all that so I caved and have agreed to the hob but hope we don’t regret it if an Elderly parent needs to move in.

I'm sure it will be okay. If elderly parent moves in, then just install good hand rails. All the best.