Putting in a downstairs toilet - crivens!!!

[billybookcase]

I was going to put a toilet "under the stairs", take the soil pipe through the wall and join it into the existing soil stack, near ground level.

I just read a post on another forum that says:

"If vent (stench) pipe is actually a soil pipe, with existing WC connection above, a ground level branch will probably be in contravention of the building regulations H1, which prohibit branches within a certain distance of drain invert."

Is this true, and what is a drain invert?

 

[hi-spec plumbing heating]

http://pdf.hunterplastics.co.uk/pdf/underground/ugt5.pdf

read page 2

 

[billybookcase]

Thanks Hi-spec, how do I know where the invert is if it's under concrete?
Is there a "standard depth" that they are set under the ground level?