Underslab drains, lintels

[WWilts]

Do the underslab drains go best in the hardcore layer or the ground beneath, or partly in each? Maximum distance 11m to get the drain out of the footprint.

 

Would you use one concrete lintel for each leaf of cavity wall or one wide lintel spanning both leaves?

[tonyshouse]

Two lintels, 100mm of concrete seems a bit thin to me, 50mm sand has been discussed before but I have seen it percolate into the hardcore leaving a void so never use it , drain in or below the hardcore is best 

[PeterW]

Your stack rest bends will dictate the initial depth as will Part H as there is a minimum depth between WC outlet and the bottom of the bend. 

[WWilts]

1 hour ago, PeterW said:

Part H as there is a minimum depth between WC outlet and the bottom of the bend. 

1.3m max?

[tonyshouse]

600 in my book  and if no one looking 500 too 

Edited July 15, 2021 by tonyshouse

[PeterW]

7 hours ago, WWilts said:

1.3m max?

That’s a direct connection distance you’re referring to. 
 

This is the min which is 450mm

 

 

[WWilts]

39 minutes ago, PeterW said:

This is the min which is 450mm

Understood now, thanks.

 

How about connecting a sink or shower drain into the underslab WC drain (after the invert)? Is that allowed?

[PeterW]

Just now, WWilts said:

Understood now, thanks.

 

How about connecting a sink or shower drain into the underslab WC drain (after the invert)? Is that allowed?

Yes but needs planning - you ideally want to go into the side and with the flow, not tee it into the top. 
 

Has this not all been done for your building regs drawings by the architect or AT..??

[WWilts]

Private BC inspector.
Builder & groundworks subcontractor have considerable leeway in rearranging sanitaryware and underground drainage.

BC will ensure compliance with regulations.

Just trying to understand the pros and cons of options/alternatives.