I just started my BEng, so I actually don't feel ready to assess real cases.
Upper floor of my quite standard British terraced house. We would like to hide an existing drainage pipe which is currently running along the wall. To do that, I cannot find other ways but running it through the pictured floor joist (I already removed the plywood underfloor, as you can see). Now, I am very wary of introducing possible structural weakenings when boring the joist: its sizes are 7cm (parallel to the floor) by 20cm (perpendicularly to the floor). Since the outer diameter of the drain pipe is 43mm (even less if use solven weld), I should be fine according to the information I found from multiple sources on the internet (maximum 1/3 of the height of the joist, hole centered and away at least 2" from the highest and lowest faces of the joist).
However, I'd really like to have further certainty for my specific case: maybe somebody who knows about these things could have a look at the picture and the data I provided and confirm this is the case? Alternatively, should I hire a (real:) structural engineer for a proper consultation on this single issue? Or would that be overkill?
I'll be glad to hear anything you might have to suggest/explain/add.