Can you use 40mm pipe for a shower drain?

[dinjang007]

I am planning on renovating my 2nd bathroom and are hoping to move the shower to where the vanity currently is. My current vanity drainpipe is 40mm and shower drainpipe is 50mm. My question is, is it worth smashing the concrete slab to change the current 40mm pipe (vanity pipe) to the recommended 50mm or I can still use 40mm pipe for shower drain? 

As I have a tight budget for this renovation, I am trying to do this work myself.

Thanks in advance!

[MitchellMc]

Welcome to the Bunnings Workshop community @dinjang007. It's brilliant to have you join us, and many thanks for your question about bathroom plumbing.

There are regulations that apply to the size of pipe from the shower waste through the slab. I believe the minimum size allowed is typically 50mm. However, I understand that the 50mm is then required to be connected to a minimum pipe size of 65mm under the slab. That's where you'll come unstuck, as your 40mm pipe will probably continue at that diameter once under the slab.

You'll obviously need to have a plumber complete all this work, and I would suggest your best bet is to speak with a few to find out what options they can suggest.

Please let me know if you have any questions.

Mitchell

[SensibleHill]

Hi this is basically what we did, put the shower where the bath was and the plumber said the drain hole was required to be larger for the shower. We paid them to do the concrete removal, drain pipes, reverse flow valve and the water piping for about $3k. 

https://www.workshop.bunnings.com.au/t5/Bathroom-and-Laundry/How-much-bathroom-floor-demolition-rest...

It was much easier for me to leave them to do the concrete, because they could get the right tools and location. For our slab it turned out to be quite thin where the bath had been, about 6cm, and next to the wall where the shower was it increased to like 20cm, with rebar through.