Hey guys,

I’m after some advice on the typical clearance required for WC waste pipe installations.

I’m working on a project with a 125mm thick floor slab, with a lattice of ground beams below the slab. A WC with a 100ø PVC waste sitting over one of the ground beams is shown in the sketch attached/below.

 Currently the structural engineer has allowed 300mm from the top of the floor slab to the top of the ground beam (the measurement labelled ? on the sketch). This allows 175mm clearance within the ground between the floor slab and the ground beam.

•   What is the recommended minimum length of straight vertical pipe from the bottom of the WC to the top of the 88° Bend (female & female socket ends)? Or does it not matter?
•   Is it better to have the entirety of the 88° Bend below the slab?
o   Similarly, are there any reasons to avoid casting a portion of the socket end of the 88° Bend within the slab?
•   What is the recommended clearance above ground beams like this? Is 50mm adequate?

Can you please also offer advice for whether your answers will apply to 40ø, 50ø, & 65ø wastes penetrating similar slabs.

Thanks for the help!

Robbie Peacocke
Hydraulic Engineer
Powell Fenwick

Linkback: https://www.plumbers.nz/ask-plumbers-trade/43/wc-drainage-through-slab/2090/