Waste and soil pipe route in new bathroom

15 Jul 2017
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United Kingdom
Hi everyone,

I'm renovating an old stone cottage in Scotland, which involves installing a new bathroom on the ground floor, with new underground drainage, soil stack etc. I have architect's drawings for the building warrant, with an approximate drainage route, but I'm trying to find out the best approach for the toilet, bath and sink drainage. I've tried to attach the drawing.

I've made a hole just under floor level through the external wall for a 110mm pipe that will branch into the new SVP. Is it possible to connect the toilet, sink and bath to the 110mm pipe indoors, or should I be looking at running separate pipes for greywater to the soil stack? I was thinking that the 110mm could run as far as the bath, and the shower/bath drainage could drop into it at this point.




  • New bathroom drawing.pdf
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The bath needs it's own connection to the soil, or it will draw water out of the trap on the shower/basin
Why are you running the SVP indoors if it ends up outdoors lower down?
Hi, I've added another drawing showing a cross section that will hopefully make things clearer. The SVP is external. A 110mm soil pipe will run from the toilet and connect to the SVP. I'm trying to figure out what the best approach for the bath and basin is however. I don't think I can connect to the SVP below the access branch, as it's too close to the invert. Is it possible for the basin and bath to connect indoors to the soil pipe, before it reaches the SVP, so there is only one pipe going through the wall meeting the SVP? Or should I go for a different approach?

Also, I'm guessing I might need a vent higher up (the red line), but perhaps there is another approach, such as an AAV or anti-syphon device.



  • bathroom drainage cross section.jpg
    bathroom drainage cross section.jpg
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The soil level is just higher than the branch connection to the SVP at the moment. The spigot outlet from the toilet will be above the soil level; the soil level is about level with the floorboards indoors (which isn't ideal for damp etc).

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