running a 2nd wc soil pipe into existing wc horizontal run ?

[lee37]

i am looking at fitting an en suite wc in an upstairs bedroom and my vertical soil pipe is a real pig to get at , even using a slip fitting i dont think i can tap into it . I can however easily tap into a horizontal run that comes from another wc downstairs, it would go something like , original wc , into- 92.5 bend , almost straight into a swept T ( connecting to new soil run ) then around 30cm later straight into the soil stack .
Would i get problems with waste coming into the lower downstairs wc that i am tapping into ?

 

[lee37]

just been looking at fittings online and it looks like i'd be best using a y peice instead of a swept T , just adding a 45 degree coupler to that to get a better aim at the drain ??!!

 

[lee37]

also if it would work would it contravene building regs ??

 

[danlightbulb]

You might have a problem with trap syphonage of your downstairs wc. This is due to the suction of the water pouring down from upstairs.

 

[lee37]

what if i add an air admittance valve to the downstairs wc ?

the soil going into it from the new loo will also carry a basin and shower waste , would that affect anything over just the wc ?

i think i may be able to tap into the vertical stack now , just means a lot of plaster board and wall removal , with some swearing also !! so obviously i would prefer to go into the horizontal run , it would enter only about a foot away from the vertical stack with the downstairs wc a further foot behind it . if that helps visualise the situation , thanks for reply , keep them coming !

 

[danlightbulb]

I would think the basin and shower waste would be minimal compared to the rush of water you get with a toilet.

I'm not sure about the practicalities of what you are proposing, someone else may advise, but I would be worried about the following:

1. Trap syphonage (not sure about air admittance valve)
2. Hydraulics (could water come out your downstairs toilet?)
3. Downstream blockage would definately cause toilet water to come out downstairs.

Water will always find the easiest path, but if the pressure head of water is high and the back pressure invoked in the soil pipework from the high flow is high then water may come out downstairs.

 

[lee37]

thanks dan , i think i will take the hard option and get it going straight into the vertical stack .. i'm sure the extra work will be time well spent if the other option failed ..