I'm guessing this house isn't built right on the slab. My house is built such that the first floor is, structurally, the second, with a crawl space underneath. To run the electricity, water, whatever, to anything you just go underneath the house, drill a hole in the floor, and run your stuff up through it.
That's how they used to do things up until about the 1960's. Now most houses are built directly on the slab unless they have a basement. Houses with crawlspaces usually don't have a slab underneath, but piers supporting joists.
I have concrete lining the bottom of my crawl space. The walls are concrete. IDK if it is a "slab" . It might be a basement except that it's just not very tall, so you can't use it as a room. Most houses around here have a basement. IDK if it's because they are old. It's very wet here, so it could be because you don't want your stuff close to ground level.
Or they could have a basement. Super easy at that point. You don't even have to drill sideways into studs behind drywall. Even easier to go up and down than around a walls. Maybe that's the answer. It actually was easier for the electrician.
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