110mm soil pipe vs 225mm metal web joists

[Oz07]

Has anyone successfully ran any length of soil pipe perpendicular in pozi joists? Im thinking each cord being around 45mm gives you 135mm between so 25mm. Maybe gives you room for a couple of metres of fall at 1:80 if you can specify the metal webs to give you room. Just considering the design of something and which way to run joists. I've also seen jobs where the joists stop short of the wall by a couple of hundred mm and sit on a trimmer like a staircase. Maybe there's even some obscure pipe size you can use for waste like 90mm od?

[Nickfromwales]

13 minutes ago, Oz07 said:

Has anyone successfully ran any length of soil pipe perpendicular in pozi joists? Im thinking each cord being around 45mm gives you 135mm between so 25mm. Maybe gives you room for a couple of metres of fall at 1:80 if you can specify the metal webs to give you room. Just considering the design of something and which way to run joists. I've also seen jobs where the joists stop short of the wall by a couple of hundred mm and sit on a trimmer like a staircase. Maybe there's even some obscure pipe size you can use for waste like 90mm od?

I do this on nearly every project, and never been an issue.

 

BCO's tend to not really give 2 hoots about the drainage after you're above ground btw, with the last BCO stating to me "if it blocks they won't ring me they'll ring you". They just ask about access, air admittance, and after that they switch off.

 

What distance do you need to travel between chords? 5m to 6m is easily doable as the flush velocity helps a lot, and 1:100 is fine as long as it's kept as a straight run. If there's need for change of direction to align with the voids, then do that at the WC end.

 

A pic or plan would help.

[Mr Punter]

You could use 82mm soil pipe to gain an extra 28mm.  Plenty of fittings available.

 

https://plasticsuppliesdirect.co.uk/soil-vent-systems/82mm-push-fit-soil-vent-pipe.html?p=2

[saveasteading]

1 hour ago, Nickfromwales said:

1:100 is fine as long as it's

But I'd be very precise and use lots of ties to the joists: wire or straps, so that it keeps the slope and doesn't ever sag. Maybe lay a timber under it where possible.

[Oz07]

Interesting. Just at very early planning stage so nothing concrete yet. I think the wall hung wcs have that 82mm soil pipe from memory? Can you come out of a normal wc pan into 82mm without problems?

 

So my option is smaller waste or less fall. Max run would be 4m, prob a bit less. I'll have to remember to feed waste pipe in when putting joists on. I did it last time with a 2" pipe and small joists centres saved having to try thread it in after. 

[G and J]

I’m sure our geberit cisterns have a 90mm bend connector thingy which then pushes into a 110mm to 90mm reducer.  
 

Early in the process I’d planned a soil pipe through posijoists but realised it was just too difficult to actually fit so I replanned to avoid the need.