New Soil Pipe Routing Problem

20 Mar 2006
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United Kingdom
Exisiting underground soil pipe runs from rear of property (bungalow) and connects to an inspection chamber at driveway entrance where it connects to the main sewer, this run is approx 26 m. As the bathroom is being moved and an extension built in the near future, a new soil pipe will have to run round the opposite side of the property, a slightly shorter run at 22 m.

Obviously the depth underground of this new pipe is governed by the connection point at the aforementioned last inspection chamber, but this is not that deep, approx 500 mm below ground level to the bottom of the pipe. Now with the required minimum fall of 25 mm /m the connection point at the new bathroom works out at only 330 mm (centre of toilet outlet to bottom of soil pipe), but the regs state a minimum vertical drop of 450 mm.

So, which is more important the correct minimum fall of 25 mm /m, or this vertical distance of 450 mm, as I can’t make it work with both. Obviously the existing route works just fine, and that’s a longer distance. For info, this new soil pipe will only serve one toilet, basin, bath and shower, all of which are on the ground floor.

Also, with such a short drop from toilet outlet to soil pipe, how crucial is it to use a long radius ‘rest bend’ at the base of the stack?

Many thanks.
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Interesting one , that... and I am of the opinion that the bend @ the bottom and the distance are for stacks of more than 1 storey. You could check with your Build Control Officer- also you could go as low as 1:80 with plastic underground drain pipe- it will work . Just my opinions ;)
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1:40 is the correct fall of a 100mm pipe and you can go less but be careful not to get any bumps in the run which is easily done if not familiar with laying plastic drains(assuming youre usint plastic).never heard of a 450mm min drop but i only hear about BR changes when i come across them as im a one man band.

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