Depth of foul drains under raft

[lizzieuk1]

We're prepping to dig foundation and drainage out and wondering about depths for the (approx 5m) run that is going to be under the insulated raft and how low to set the foot for the main stack which exits straight out. 

Any idea what that depth needs to be? Is it 600mm below the mot 1?

 

Also, how far out from the edge of the raft do the drains need to run - I'm reading 1m min is the part H requirement if pipe is below foundation but, as our raft is only 450mm into the ground makes interpreting the regs a bit tricky as, pretty much any drain will be below the raft level.  I'm not sure if it's interpreted the same as obv the weight is spread over the raft rather than down through strip foundations so, does this make a difference?

 

Or, do I just ask BC?!

[Nickfromwales]

On the current MBC project I'm consulting on, we have soil pipes in the 150mm MOT1 layer directly under the 50mm sand blinding, and some others like comms and landscape power are lower to avoid these. I designed all this ahead of MBC's arrival, making sure there were the least number of services crossing over/under each other.

 

As you're under a raft, there is no minimum depth THB, but for power and water you do need to drop down towards the periphery to comply with the 750-900mm that these authorities will mandate.

[Gone West]

@lizzieuk1 Our insulated raft sat on 250mm compacted type1 with 50mm granite fines on top. The insulation was 300mm thick. The inspection chamber was around 3m from the edge of the raft. The pictures show before and after sub-base was laid.