# Forum Home Renovation Plumbing  Shower Floor Waste Pipe Sizing

## gpaulid

Hi, looking for some advise. We are renovating a house with 3 bathrooms. The plumber has been in and did most of the initial work. In the upstairs main bathroom (for the kids) he has used a 50mm diametre pipe for the shower waste. I have had 3 waterproofers in for quotes and one said that I need a larger diametre pipe for the shower ideally. I am not sure what the standard dictate. Need to correct if needed now before the plaster comes in to finish off ceiling below this bathroom.  
For one of the other ground floor bathrooms the pipe seems to be over 90mm in diametre (on concrete slab). In the ensuite (concrete slab) looks like the drain is 100cm but the pipe within goes down to 50mm. 
Can anyone advise? Thanks in advance.

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## Oldsaltoz

Not a real problem in that a 50 mm drain will keep up with a showers output, you need to know what size pipe is under the floor, but, don't let this get to you, there are thousands of upper floor showers with 50 mm flanges. 
Hope this helps, 
Good luck.  :Smilie:  
PS both mine are 50 mm and no problems in 15 years.

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## heavytrevy

50mm is fine,make sure u fit a 50/80 grate .

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## wonderplumb

50mm is OK but the grate needs to be a minimum of 80mm

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## Oldsaltoz

Both mine still have the 50 mm grate from 15 years ago.

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## gpaulid

Thanks to all who replied.

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## jacdav069

Looks like gpaulid got his answer so I will ask a similar question.
We are planning on renovating our ensuite later in the year, and are hoping to move the shower to where the vanity currently is. My question is, is it worth smashing the concrete slab to change the current 40mm pipe to the recommended 50mm. 
Cheers Dave..

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## reno909

Yes it will need to be changed

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## jacdav069

I just noticed the bath in our bathroom has a 40mm plug, so I presume a 40mm waste pipe. If the bath has 40mm maybe I can get away with 40mm for the shower waste pipe size. Surely the 40mm pipe could handle the flow from a single shower head. 
I have done this once before when we changed a bedroom to a bathroom, not a nice job at all! What do the professionals advise? 
Cheers Dave

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## heavytrevy

50mm with a 50mm grate is the old standard.
nowadays is 50mm pipe with a 80mm grate. 
40mm is to small

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## sydneytom

the bath waste is run in 40mm to limit the flow of water through it when the plug is pulled, this prevents water seals in nearby traps from being sucked out due to the reduced amount of water gushing past. i've always preferred running a 100mm shower drain then using what they call a pot gully to reduce down to 50mm. it's just a regular gully or trap with a 100mm inlet and a 50mm outlet, that way it enables you to reach down with your hand and clean it out if it ever blocks, which they often do as a result of dodgy tilers dumping grout and mud down them! but a 50mm drain is still fine to use and legal.                                                                                                                          regards tom

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## wonderplumb

The idea of a 40mm waste on baths these days is to stop that horrid sucking noise they used to make, and of course to stop it sucking it's own seal.
As tom said use a 4"x2'' pot under the shower, this also stops a draught coming up out of the waste while you're in the shower.

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