Does a horizontal soil pipe have to run within/below the floor slab?

[LJD1974]

We have a new soil pipe entering the house with the top of the pipe sitting at the same level as the where the top of the slab will sit. To maintain the correct fall along 3m to the WC, it would have to rise by 75mm, which eats into a 100mm insulation layer (before 50mm screed goes on top) and doesn't sound great to me, and I'm also concerned about the possible water noises coming up through.
What are the rules around soil pipes? Should they sit entirely within/below the slab? Thanks!

 

[Hugh Jaleak]

I've always been told they need to be encased in concrete to protect the pipe. If need be, bring it up through the floor earlier in the run, then do the last section to the pan above the floor, going into a Stub Stack.

Pipework above floor level can be boxed in, the concern is if too shallow below the floor, it is very susceptible to damage.