How does plumbong work if house is on a slab?

The drain lies are installed in trenches and filled in before the slab is poured. Water supply lines run overhead and down the walls behind the fixtures. This is done right after framing and prior to insulation or wall covering of course. All the necessary pressure testing is done before covering any pipes.

OR the supply lines are also run in trenches and come up through the slab at each fixture site. This method is used most frequently in colder climates to avoid freezing in walls.

That is true. Years ago before houses were required to be fully insulated, this was done. Today in most areas, underground supply lines are extremely rare. Modern insulation keeps pipes from freezing and metal supply lines do not corrode as they do when buried. I have seen it done both ways. In commercial buildings, supply lines are almost always run in the ground under the slabs, because of the nature of the structures. Most recently plastic lines with distribution valves have become common in the housing sector. I have never seen these lines used below grade, but I suppose they could be.

Tried to give ball a thumbs up, but they said I was frequenting too much praise.

I think it is a regional thing, I'm in the midwest and we never see pipes in the attic because they can sweat and ruin the drywall. And, you loss a lot of energy running hot water into an attic space. I think maybe you work in a more moderate climate.

Jimmy, here is what ABS under-slab rough-in looks like. You are looking at portion of guest bathroom underground plumbing. In front of you is toilet with clean out extending through forms. On the left is tub. Sink on the right. ( The other pipe left of sink drain is a vent from the toilet ).

This is a 12" slab. ABS pipes are wrapped with plastic wrap. This wrap creates separation between the pipe and concrete.

Process of building a house goes very fast. There is no time for thinking or mistakes. As you can see from the picture, forming on this 6,000 sq.feet spec house have just about began - and we already started on installation of underground drain system. Couple of hours after this pic was taken - rebar people began with their installation. Trust me, rebar guys are the last guys on the job site you wanna slow down ... !

Plumber has to measure his distances correctly because once you pour your slab - than there is very little you can do to move your drains. If you screw up, than this may be your last job under this contractor.

Toilets have to be set exactly to prevent "NatalieBlueEyes" effect. ( that is : undesirable gap between wall and tank ). Additionally, shower drains have to be centered too. Every other plumbing fixtures has some built-in slack that can be corrected later on with above-slab installation.

By Plumbing Code in my region, we have to run our water supplies in walls and ceilings. We install 1/2" jacket insulation on hot and cold pipes. Only exeption is water supply to kitchen island. Gas system is also installed in the attic.

Hope this will answer your question...

Generally, here in the west, they can the shower and tub drains. When they set the trap, the hole is filled with sand covered with quick-crete. The framer generally checks the toilet bin when he lays out the bath wall. That's why everything fits so well. Or at least as well as it does.

I say thanks to milo, a picture says a lot more than any of us can.

By Plumbing Code in my region, we have to run our water supplies in walls and ceilings.(Milo) Water supply lines run overhead and down the walls behind the fixtures (bandit)
In the Tampa Bay Area all our buildings are on slabs. The only time we run our water in the attic is if we are on a remodel. Our new work is installed under the slab using type "L" seamless soft copper brought up above ground in a wall to a manifold and then back down out in branches. Or at least that's how we did it when I was out in the field. The reason being that if there was a leak under the slab then it wouldn't rain down on your furnishings like it wouldf if it were piped overhead. Just goes to show you! Different area, different codes, different methods. Regards, Tom

Tom's description matches my #3, hot Tampa or cold Chicago we usually do our rough ins under the slab.