I too want to add a WC to the en-suite which is next door to the bathroom. So, if you were looking through the bathroom door at the back of the house the vented soil stack is in the right hand corner, I want to run about 1.2m of 4" under the floor (the 8" joists run the right way) to a T which connects to the bathroom WC and then about 800mm of 4" to a swept elbow for the ensuite WC just the other side of the wall. As both pans will be dropping vertically down into the 4" soil it never occurred to me that there could be an issue until I read the other post! Are there any issues? Cheers!
Well I wouldn't have a clue how to do that Dave! Anyway I'm doing the job on Weds so if it doesn't work and I go bankrupt I'll be sure to let you all know!!
If your running the two pipes into one stack as separate pipes then it shouldn't be a problem, the other post I think your talking about was two wcs on one pipe that went to the stack, in that case a AAV needs to be fitted to stop vacuum suction emptying the trap on one of the wcs when the other is flushed.
A corner branch might have been easier? http://www.lowcostplumbingsupplies.co.uk/110mm-corner-branch-90-degree-p3888 Can find cheaper if you hunt around, last one I used, came off the bay for £30.
No it's two WC's into one branch. Do you think I could get away with a 50mm AAV as I could hide that within the stud wall?
Usually it's 82mm minimum used on stacks, wouldn't like to commit myself to say 50mm would be ok. Just had a look at FloPlast AAV info,linky below, you ain't going to get the required airflow. http://www.ribaproductselector.com/Docs/5/12945/external/COL912945.pdf
Thanks KIAB. I'm not going to risk it so will build a box behind WC and fit a 4" stack and Dirgo. Cheers all.