Basically, can I send a vent stack horizontal for a couple feet only 3-6 inches above the toilet drain before sending it vertical again.
Here's the story: I'm remoddeling my poky little multi-room bathroom into one big bathroom and a closet. I planned on turning around the toilet 180 degrees in it's same location and put a longer wider bath tub on the same drain but rotated 180 degrees and slid 6 feet. The problem is that I'll have to move two vent stacks. I'm not sure if the configuration of this plumbing is the greatest and follows all code but it's been working fine for as long as we know, other than the low flow toilet takes two flushes. So I figure on just moving the stacks and making minimal changes to the drainage.
Now the crux is that the toilet drain is a long sweep and ends up about 1 foot under the top of the foundation from which the vent vertically tees off. I want cut down into the foundation and around the vent, put an 90deg 1.5" elbow on top and a 1.5" inch 24" long horizontal pipe in the cut away foundation (hopefully a 3" deep cut) and then go vertical in the wall and into the attic. Once it's in the attic I'll have to put an angle on it and route it to the original exhaust pipe in the roof.
Ready for the question now?
So how close to toilet drain can I turn the vent stack horizontal? I'm hoping 6inches or even less is fine.
A second question is how thick does the foundation have to be above a vent stack pipe? FYI, ontop of the foundation, I'll put 1/2 inch thick travertine tiles. So I'm hoping an inch of foundation over the pipe is fine. ;-)
Otherwise I figure on pouring an elevated stand for the toilet and putting an extension on top of the toilet drain to meet the new hight a few inches higher, but I'd rather not do this. Other option that I can imagine would require major new holes in the foundation, which I'm trying to avoid! Plus the toilet drain is lead and I'd prefer not to mess with that either. ;-(
I've attached a diagram, and I have many detailed pictures I can add if you need.
Thanks for your patients and assistance. I did read through the Houston code and many many post on your site before posting this myself.