Lowering a soil stack connection

[SuzieJarvis]

Hi all,
First post here, so please bear with me.....

I am about to start ripping out the en-suite and totally refitting it. One of the key issues is getting the correct fall from the new shower waste to the soil stack. The existing shower tray has been jacked up by around 150mm, but I would like to install the new tray as low as possible.

If I have understood correctly, the fall on the waste should be around 20mm to 25mm per linear metre of waste pipe run? If so, I may need to lower the connection into the soil stack... The stack will be relatively easily accessible in the en-suite, as I will be removing riser and wall lining panels, floor boards, etc. However, the riser containing the stack then continues through my living room (yeah, great!) and as the living room has recently been redecorated I am loathe to break into the riser there.

Is it quite simple to lower the conncestion into the soil stack? Obviously the WC pipe connects at the same point, but could I cap off the existing shower waste/stack connection and connect a new one a bit lower down without buggering up the WC connection?

Until I get the floor up I won't know the waste pipe layout for sure, but it would appear from the builders plans that the pipe runs diagonally through the floor void! Not sure how this would work with minor obstructions like joists in the way... IF the soil stack is diagonally opposite the shower outlet, should I be running the new waste around the wall above floor level?

I know, I know... so many questions... But if anyone is still with me (and awake) any advice would be greatfully received.

Many thanks, SJ

 

[Bahco]

Best to have the shower tray 6 ins high so that you can access the trap for cleaning.
If you bury the trap in the floor you may need to cut into the downstairs ceilinhhg one day to get at it.

Leave it be and use existing connection.

 

[Richard C]

If I have understood correctly, the fall on the waste should be around 20mm to 25mm per linear metre of waste pipe run?

fall is 18-90mm/m; maximum unvented waste run is 3m for 40mm, 4m for 50mm then you need to fit either an air admittance valve or self venting trap.

Is it quite simple to lower the conncestion into the soil stack? Obviously the WC pipe connects at the same point, but could I cap off the existing shower waste/stack connection and connect a new one a bit lower down without b*****r up the WC connection?

You can do that or cut a lump out of the stack (the exiting waste connection) & fit a new waste boss collar; the existing waste run should have a separate connection to the stack, not sure I’ve got you but are you saying it’s combined with the w/c? Not sure why it would bugger the w/c connection!

Until I get the floor up I won't know the waste pipe layout for sure, but it would appear from the builders plans that the pipe runs diagonally through the floor void! Not sure how this would work with minor obstructions like joists in the way...

Do not be tempted to cut the joists to run the waste pipe unless it’s already been done

IF the soil stack is diagonally opposite the shower outlet, should I be running the new waste around the wall above floor level?

You may have a problem getting enough fall to do that, unless you jack the shower up even higher; it doesn’t look particularly nice either. It’s usually less noticeable to drop through the ceiling with the run & box in there but it depends on layout.