What is the height of the finished slab in the garage relative to the finish floor inside the house? Also, are your floor joists inside the foundation, or do they sit on top of the foundation?

Hey thanks for response, the slab in the garage looks to be 6” thick bare slab, if i dig down to look. Showing level though with ground. Sits up a bit no rain flooding ever in there. Garage is detached and house is on approx. 2’ Bois’ d arc beams.

No floor joists in garage

Maybe bump out is wrong term, i might be asking about just a ‘add on’ for bathroom to suffice my problem of ‘down’ out main drains to my original sewer under the main house. But coming off the cement slab and how the other water lines connect to it is what i don’t understand. I don’t need the extra area of sq foot for the bathroom, just not wanting to raise the floor in there, for plumbing, although if i do i will have just enough height to keep a 7’ clearance for inspection.

Bspoke Homes, does this sound like a possible solution for my new plumbing?

I think I understand what you are saying. You are planning on adding a room to the exterior of your garage that would essentially be your bathroom. Of course if this is your plan, you could certainly do the plumbing prior to pouring the slab, but you would need to add a foundation for this room in most areas (have to check local plumbing codes). If that is your idea, unless you need the space, you would spend more money going that route than simply saw cutting your existing garage floor to add for your toilet and other drains.

If you don't already have water lines in the garage, the water lines would simply come over in the same trench as your waste line that goes to the house. The actual plumbing work will be similar regardless of if you did the bump out addition.

The saw cutting can be done by a concrete cutting company if your plumber doesn't want to do it, but it is common for plumbers that do remodel work to do contract the concrete work or do it themselves.

Bottom line. If you don't need the space, in my opinion, I would keep the bathroom in the existing garage area and saw cut as it would be less expensive.

The permits and requirements for an addition are different than for a remodel. The correct and standard SOP way to do this is to cut up the garage slab to get the pipes where you need them. Is your architect not familiar with garage conversions?

Bspoke i hear what your saying, thanks. If the slab is only what maybe 5 inches thick do you think it will hurt the ‘integrity’ of the foundation? I‘m hoping that I asked that correctly and i know you can’t guarantee something like that, but what are your thoughts? And, is the potty drain area the only place they have to dig, and probably shower?

The Cook’s Kitchen i have to say i do not have an architect for this project. Have a GC and he suggested cutting the concrete in the first place. I was afraid the slab might crack so we discussed raising the floor but i really was trying not to go that route. To keep from losing head space throughout.

You said the slab is 6" as you dug down to check. Is there a thickened slab or foundation around the perimeter? Does the garage slab slope? Most do.

I don’t think it slopes and it’s just one flat slab garage. I’m sure it will need to be floated though for some leveling.

Your toilet requires a 3" drain which is probably the size they would run over to your house to tie into the existing. Both the sink and toilet would also be tied into this same drain under the slab. With regards to your concerns about the slab cracking from saw cutting. No, this shouldn't be an issue. As it relates to your slab and the foundation, you are correct, this we could not tell without seeing pictures or having a better understanding of what your outbuilding is. In the grand scheme of things as it pertains to the plumbing specifically, the only thing the foundation will really play a roll in is the plumber will either have to drill through the wall itself to get out of the garage, or dig under the footing itself if there is one. The second scenario may not be feasible as you most likely would have issue getting grade over to the existing drain you will be tying into. One thing to keep in mind is the number of existing toilets you have in the house. Depending on the code your local area has adopted, if you only have a 3" drain going out to your sewer/septic, you can only have 2 toilets on that drain (some jurisdictions will give you a pass and allow a 3rd. If you already have 3 toilets inside the house, make sure your drain out to the street or septic is a minimum of 4" or you will be dealing with up sizing the main drain as well from your house.