Vertical section in 110mm soil branch pipe?

[Rob98]

I'm planning a DIY 1st floor bathroom refit, and ideally want to move the position of the toilet by about 50cm further away from the vertical soil pipe than the existing toilet. I'm aware that anything much more than like-for-like replacement is likely to need building control approval, but if it's not possible to move the toilet I just need to change the plans at this stage rather than waste their time!

Current Setup

:

The current horizontal run is 150cm to the vertical downpipe outside the building. Unfortunately the floorboards run in the wrong direction. The existing installation deals with this with a vertical drop from the toilet straight through the floor, and then a horizontal 150cm run along the ceiling of the room below (boxed in) until it exits through the external wall. As best as I can measure it this section falls at exactly 18mm/m, and I can't lower the far end (it exits just above a lintel).

What I want:

I can't extend the pipe any further to the left in the room below the bathroom as there isn't the space for the 18mm/m fall without notching the underside of the joists (by 9mm - probably makes no real mechanical difference, but against the rules!). Can I extend the soil pipe horizontally within the bathroom? This would mean 50cm of downwards slope, 30cm vertical, then another 150cm horizontal. I guess if I used standard 92.5 bends for this I might get blockages at the bottom of the vertical section, but is it doable with swept bends of some sort (like the underground one at the bottom of the vertical soil stack)? Any other ideas?

Thanks

Edited to fix image links

 

[oldbutnotdead]

Any reason you can't go straight out through the external wall behind the loo then across to the stack externally? That would get my vote- only 1 bend, easy access for rodding, you could lose the boxing in the room below, winner winner chicken dinner

 

[Rob98]

I'd love to, but the wall behind the loo isn't external. The nearest external wall to the loo is the one on the right of the picture 2m away. The room below is a garage so boxing not a particular problem, and can put a rodding access point in there too if needs be.

 

[oldbutnotdead]

Ah, can see your sketches now. Can you not run along the wall behind the loo to outside, then into the stack? Tbh, your original sketch would probably work anyway, bonus is the garage being below so access for rodding isn't an issue. The new downward bend can be standard 92.5, the existing across bend works now so should work in the future

 

[dilalio]

It'll be fine. Just extend it. I've had to go dead level before a fall, many times before and not had an issue. Just put an access branch in to cover yourself (in sh!t if it ever gets blocked )

 

[Rob98]

Thank you both. Right along the wall also doesn't work because it would cross the entrance to the room. I'll go with my original plan then.