Minimum Toilet Soil Pipe Diameter

[MortarThePoint]

I know using a macerator you can get the pipe diameter down to an incredible 22mm [link]. But macerators can be noising and go wrong as well as being costly. What is the minimum diameter pipe that can be used for a toilet waste without a macerator?

[Conor]

Wouldn't go less than the standard 110mm. Many toilets have 90mm pan connectors but you do t see 90mm soil pipes.

[MortarThePoint]

53 minutes ago, Conor said:

Wouldn't go less than the standard 110mm. Many toilets have 90mm pan connectors but you do t see 90mm soil pipes.

 

I know it's not ideal, but I need to work out a smaller size if I can. I see in Part H the paragraph below. Am I to understand from that it's OK to have a 75mm waste pipe from an <=80mm outlet toilet:

 

https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/442889/BR_PDF_AD_H_2015.pdf

[Temp]

I would also avoid going smaller. 

 

I think the next standard size down from 110mm is 82mm but I would only use if no alternative. I'd also keep the 82mm section as simple and short as possible. Make sure it can be rodded. 

 

Perhaps if you explain the situation we can think of a better solution?

[Mr Punter]

110mm is standard and cheap, fittings are easy to come by and easy to clear / rod.  Why do you want smaller?

[Mike]

2 hours ago, MortarThePoint said:

Am I to understand from that it's OK to have a 75mm waste pipe from an <=80mm outlet toilet:

1.28 is referring to the vertical stack, not the connection to the WC.

 

The part between the WC and the stack is the 'branch connection'. So the rule at 1.15 applies and for an 80mm outlet toilet you either need a minimum 80mm or 75mm pipe. But, as Temp says, in practice you're limited by what's on the market. And I too would stick to 110mm - unblocking drains isn't my idea of fun.

 

[MortarThePoint]

8 hours ago, Temp said:

Perhaps if you explain the situation we can think of a better solution?

 

8 hours ago, Mr Punter said:

Why do you want smaller?

 

I want to send the pipe through a couple of truss bottom chords (222mm) and the truss designer has said 115mm hole too large but 80mm would be Ok 

[Russell griffiths]

3 hours ago, MortarThePoint said:

 

 

I want to send the pipe through a couple of truss bottom chords (222mm) and the truss designer has said 115mm hole too large but 80mm would be Ok 

Tell the truss designers to design in a steel reinforcement plate. 

222mm deep 750 long with a 110mm hole in them, glued and bolted both sides. 

 

He probably thinks you just just want to blast a big hole in his bottom cord, everything is doable as long as you then don’t nit pick his reinforcement design, by then saying the metal is too expensive. 

 

Do a sketch of your proposal and send send it over to them. 

[MikeSharp01]

4 minutes ago, Russell griffiths said:

Tell the truss designers to design in a steel reinforcement plate. 

222mm deep 750 long with a 110mm hole in them, glued and bolted both sides. 

+1 to that with steel you can reduce the bottom cord to 6mm thick provided the load is spread back to the rest of the beam correctly and the whole lot is fixed to the structure properly.

[Temp]

+2

 

I've seen it done with simple angle irons bolted top and bottom but best get it designed.  From google images...

 

[MortarThePoint]

On 24/08/2023 at 13:40, Temp said:

+2

 

I've seen it done with simple angle irons bolted top and bottom but best get it designed.  From google images...

 

 

One of those (the middle one I think) can be shipped from the US now. The one on the right is just for i-Joists.

Looks to be the way to achieve a bigger pipe.

[Russell griffiths]

1 hour ago, MortarThePoint said:

 

One of those (the middle one I think) can be shipped from the US now. The one on the right is just for i-Joists.

Looks to be the way to achieve a bigger pipe.

But you still need it to go via the truss designer, none of us know what your trusses are holding up. 

[Gus Potter]

On 23/08/2023 at 18:07, MortarThePoint said:

What is the minimum diameter pipe that can be used for a toilet waste without a macerator?

Extracts from BS EN 12056 - 2:2000

 

For a WC the pipe diameter hinges on the outlet size.. which kind of makes sense..

 

 

[Gus Potter]

On 24/08/2023 at 06:07, MortarThePoint said:

I want to send the pipe through a couple of truss bottom chords (222mm) and the truss designer has said 115mm hole too large but 80mm would be Ok

Can you bridle around the area like you would do a stairwell, now you don't need to hole the bottom truss chords?  Maybe you need to double up the bottom chords or make the trusses if Engineered with a thicker flange or if standard trusses make these out of a thicker (not deeper) timber. That may make the problem go away and give you much more play vertically and horizontally when you actually install the WC.