Plumbing through beams

[SomePenguin]

With what you said in mind, I quite strongly advise against it. The hole-making doesn't seem absolutely necessary. 70x220 may be an impressive dimension, but with a 6 m span, you have no margins. When making large holes in beams, there are two areas you should avoid: Midway along the length and near the supports (the supports for the beams). The hole should be made at half the height of the beam. The problem with drainpipes is that they need to have a slope, and therefore the holes are often in the wrong height. A sink drain can be routed on the wall up to the vertical stack.

Yes, I have been considering continuing with 2 stacks to avoid the hole-making. But I wanted advice and discouragement about the alternative to combine the stacks to facilitate a complete pipe replacement and remove the old cast iron pipes.

So if the choice is:
1) hole-making + pipe replacement
Or
2) keep 2 stacks + 1 cast iron pipe from 1938.

Alternative 3 to replace both stacks is maybe or maybe not possible, and it remains to be examined more closely.

I'm trying to understand my options here, so your opinion is appreciated

 

[SomePenguin]

Update:
The solution was a round borehole for 75mm pipes and then 22mm plywood that was glue-screwed on both sides of the beams.

There is a load-bearing wall on the floor below, so the beam span is probably "only" 3m.