Annex drainage under concrete slab

[BenGillyHills]

Hi All, I have been discussing previous iterations of this in another section but I’m posting here with a clean slate so that previous discussions do not over-complicate.

 

I’m building an annex close to my house on our farm/smallholding. The drains will connect into existing septic tank.

 

The drains from the bathroom cannot take the shortest route to exit the building due to lack of space outside, so I am having to bring the pipe under the slab to the closest poss exit location.

 

I’ve worked on several iterations of this, learning the conventions as I go. I am hoping someone who is knowledgeable on drainage can tell me if this is acceptable?

 

I’m fairly sure the configuration of HWB and Shower using Y junctions going into the main WC run is ok.

 

Also, the length of pipe running out of the building diagonally is less than 2m.

 

The potential issues I can see are:

 

- The change of direction at the first inspection chamber is more acute than 90°.

 

- The 45° long radius bend just before exiting the building.

 

- Exiting the building diagonally.

 

Given the restrictions of the site does anyone think a sympathetic BCO would accept this? Or better still, tell me this is all fine?

[Russell griffiths]

I’m not understanding your problems in your other posts. 
can you summarise 

is your concrete foundation too high in that it is stopping you exiting the building in a better location

will you not be bringing up the land around the building to cover any pipes

you want to bring the pipes out where you have a step in the footings so I’m assuming the above. 
the pipes can exit anywhere and lay on top of the footing, as long as you lintel over them there’s not a problem. 
what am I missing. 

[BenGillyHills]

2 hours ago, Russell griffiths said:

I’m not understanding your problems in your other posts. 
can you summarise 

is your concrete foundation too high in that it is stopping you exiting the building in a better location

will you not be bringing up the land around the building to cover any pipes

you want to bring the pipes out where you have a step in the footings so I’m assuming the above. 
the pipes can exit anywhere and lay on top of the footing, as long as you lintel over them there’s not a problem. 
what am I missing. 

@Russell griffiths Yes you’re right in what you say. The foundations are too high.

 

Also on the right hand side of the building when looking at plan, the passage is too narrow for inspection chambers.

 

The pipe could in theory exit along the bottom wall closer to the bathroom (under the service room) but when resting on the footing with clearance and a drop, it would be encased in the slab. to keep the pipe under the slab I would probably need x2 more courses of trench blocks (100x300x450) increasing the finished floor height, thresholds and outside ground level by 200mm+. As you say the ground outside will probably come up a bit anyway but an additional 200mm increase inside and out is a significant cost in materials, time and labour.
 

So perhaps my BCO is the only person to make a call on this (he’s away until next week) or perhaps what is detailed in my latest diagram is simply not compliant and a non-starter.

Edited Friday at 15:25 by BenGillyHills