Engineers, and lots of other people, who have worked on single-family houses have stories about plumbers cutting out significant chunks of floor joists to run drain pipes.
The picture above shows conditions uncovered in an apartment house on the Upper West Side. The green is the top of an exterior wall, the rest is the underside of the floor slab above. The plumber did a nice job remove all of the concrete along the drain – actually past the end of the horizontal run of pipe – and mangled some of the reinforcing wire in the process. But, to be fair, he made up for it by dumping a bunch of debris into the hole to cover it from above.
