Toilet & shower drainage

[rob_m]

I'm putting in a new groundfloor bathroom (toilet, shower and basin) in the middle of the house. I'm planning to run in a new 100mm waste pipe from an existing manhole by chopping a trench across one of the bedroom floors.

I have some questions I'm hoping someone can help me with.

1. Is there any minimum depth the waste pipe has to be under the bedroom floor?

2. I think the shower/basin waste and toilet connector would have to discharge into a stub stack in the new bathroom with an air admittance valve. How high does the stub stack have to be?

3. Can the shower/basin waste and toilet waste enter the stub stack at the same level (providing they are not directly opposing)?

 

[ChrisR]

1 no
2 above the flood level
3 at a pinch.

Slope in the pipe should be 1 in 40.

 

[rob_m]

Thanks ChrisR.

Before I reach for the pickaxe does "flood level" = the overtopping level of the highest attached item (in this case, the hand basin)?

 

[kevplumb]

yes

 

[felix]

Flood level is the LOWEST open rim, probably the shower tray in your case. Imagine that the new stub stack is blocked below ground. Where will water first start pouring out onto the floor?

As for joining in at the same level, you can get soil pipe Tee junctions with entry points for small pipes on either side. You cut out the plastic in one of these and solvent weld an adapter into the hole.

 

[htgeng]

Thanks ChrisR.

Before I reach for the pickaxe does "flood level" = the overtopping level of the highest attached item (in this case, the hand basin)?

woah! before you start reaching for your pickaxe you need to call your building control office and tell them what you propose to do. They will send someone to check it out and give you the forms to fill in

 

[felix]

Htgeng has a point. One of the things a building inspector will check is something you possibly haven't considered. By digging a trench across a concrete floor you are likely to breach your damp proof membrane. Also, contrary to previous advice, common sense dictates that there is a minimum depth for your pipe. You don't want it so close to the surface that somebody puts a chair leg through it!

If it was mine, I'd want it running entirely below the concrete slab - and I'm not too sure how I'd go about repairing the DPM afterwards. Come to think of it, I'd probably ask a builder!

While I'm on, I've had a second thought about that flood level business. Although flood water will escape from the shower tray first, its pipe is too small to take toilet waste. If you flush a toilet into a blocked drain you don't want it trying to come out through your air valve. Better to take flood level to be the toilet bowl rim. You'll still have to clean up the floor but the valve will stay dry.

 

[kevplumb]

yow do talk some cack
on occasions felix

 

[htgeng]

yow do talk some cack
on occasions felix

cack can't come up a shower waste? I've seen it happen and it wasn't pretty! ewww