110mm soil pipe going through raft foundation help please

[Martin17]

Hi guys I’m new on here and looking for some help!…..we’re right at the start of a self build and looking to do the majority of work ourselves!….question I have it, we have to have a raft foundation, we have 3 soil stacks going into the building in corners of the build…..for the life of my I can’t find anything to clearly show pipe work running from affl to underground…..I have bought lengths of 110mm waste pipe and a few long 87.5 bends, will this be enough to get me out of the raft?……do I need to connect a pipe into the 87.5 and both ends….1 coming right up. Through the slab and the other going underground……can the sockets be buried into concrete with only pipe coming through the slab or does the top sockeg of the 87.5 bend need to be above affl?…..sorry for the long drawn out question! Thanks in advance!

[Jenki]

Generally soil pipes use rest bends.  (A long radius with a foot). Gives the pipe extra support, I've seen people use long radius bends, but might be worth checking with BC.

The pipes usually extend  above FFL and capped to stop concrete entering the system. It's also a good idea to pressure test all this before the pour. ( In Scotland they will insist on the test.)

 

 

[Conor]

Before you do anything, find out the required inverts of the pipes so you can set them at the right depth. For this you need to know the invert at the connection point at the main sewer / septic tank and calculate back so you have the correct falls. Your ground workers should be able to do this. At this stage you just want the pipes coming out of the raft and no more, or else they just get damaged. For the pipes inside, have them terminate just above the FFL. Whether you need extra pipes on the bends depends on the depth of the pipe and thickness of your raft.

Edited November 24, 2022 by Conor

[Temp]

Will anything need to connect into these stacks just above the ffl? Plan ahead as the availability and height of branches can be limiting. Don't really want a shower tray on a 1ft high plinth.

 

 

 

[Nickfromwales]

We can advise, but you absolutely MUST get this answered by your BCO!!

If you don’t, on your head be it. 
Your paying for the privilege, so use that to your advantage, and ask all these questions directly, noting the answers. Saves doing things twice, at 4 times the price. 
Consider where these rise, as sticking them in the corners is what we did 30 years ago. I design the slabs for my clients and out the rising foul water pipes where I want them, deleting long horizontal runs and certainly zero boxing in etc. 
Don’t rush this, take some time and give it some thought. Do you want a sunken shower tray / wet room former on the ground floor? If so, you’ll need a shuttered out section of slab, and a dedicated FW riser, sunken, to take the waste from it.

 

Measure 3 or 4 times, cut once. 👍

[saveasteading]

Pipes should not be encased in concrete, but have either a gap or a protective layer around them (usually polystyrene so it can crush). Then when the building moves it doesn't break the pipe. This is in the buildong regulations.

Your designer should be giving you all the detail.

Maybe your groundworker is great and can read a drawing and do sums....but you can't count on it as many have had no training and simply go downhill using a spirit level with the bubble out of the lines. Your design mighg require more precision than that.