Hi,
We just purchased a home in L.A. built in the 60s that has a concrete slab construction. We want to add on a master bath to the house but I don't know how we would tie into the plumbing lines in this kind of a foundation. Do they actually pour concrete onto the pipes when the foundation is set? How do you find where the pipes run in the floor? Any help or information would be appreciated.
Thanks

I'm a Florida plumber and all our homes are built on slabs. We first dug trenches and laid the drainage pipes in them. Then the cement guys covered the slab with visqueen and wire mesh and poured the slab. The sewer pipes are under the cement.
A experienced plumber can walk through a house and just about know where all the drainage was roughed in by looking at it. Not having a set of floor plans makes it impossible for me to tell you the drainage layout, however, rule of thumb tells you that the drainage will follow a line from the furthest bathroom group past the outside cleanout to the sewer or septic tank.
You will tie into the existing main with a 4" fitting to pick up the toilet and branch off with 2" to pick up the tub/shower and lavatory. You will extent a vent up from the lavatory to the roof or revent back in the attic. You will take both hot and cold supplies off 3/4" mains reducing down to 1/2" to pick up the group.
This is major surgery you're considering and you'll need considerable skills, not only in plumbing, but in cement work, carpenter work. Drywall installation, tile for a shower or bathtub and electrical. Were you planing on doing the work yourself? Regards, Tom

We are planning to subcontract out for the rough work as it is all fairly complicated and try and do as much of the finishing slowly on our own to help bring down the costs. I have checked around to see if the county has the plans but unfortunately LA only has original drawings going back to the 70s. I doubt that the architect or builder would still have them.

The 10'x17' addition for the master bath & closet will be to the back right corner of the house. (I have a picture but can't figure out how to attach it) The main bath is on that corner of the house. The sunken tile tub is on that outside wall we are adding to with the toilet and vanity on the opposite interior wall.

I guess we would have to demolish the sunken tile tub to tie into the supply and waste lines. Would that give us enough access to the water, vents, and drains to do the master bath addition with shower/tub/toilet/double vanity or will we have to break into the other fixtures in the current main bath? Do you have any idea how expensive it is to have to break into the concrete and trace lines? I understand construct runs $125/sq ft but with all the demolition & concrete I have no idea if this is accurate.

Click on my name up above. Click on Send E-Mail to Speedball and attach your picture, you could also scan me a lay out diagram if you have a scanner. Sound like a plan? Tom