Just finished putting in a raised floor in the loft of my son's freshly bought (new build ) house. By 'eck, there were cables running over joists , I had to watch what I was doing I can tell you. It were never like this back in the day, all the electricals were conduited ...
By heck, tha must be owd.... Can doo it?, that's what we asked the apprentices when we left um ter dow jobs, whilst we went down't pub.
Cables running over joists? Never on my watch. I remember when serving my apprenticeship an "auld bloke" telling me my generation was the last of the real tradesmen. Oh how we laughed. Turned out to be true though. No-one seems to learn the stuff we did any more. Last time I saw any new fully tubed domestic installs was 1986 for the old Scottish Special Housing Association on a job in Glasgow. Had 2 4th year "laddies" working for me at that point who had never tubed and wired anything before.
When I wer' lad, I had to work so quick, t' tallow dripping off t'die would catch fire before hitting t'ground. ...and if you tell the young un's that....they wooont believe you ! RS
If your having to put in a second floor above the ceiling joists, the ceiling joists can't be substantial. I would say would be the type/size that should not be drilled/notched. If you're doing commercial jobs in high specked installs, you will likely find galv trunking in the loft or ceiling voids, with either PVC or galv conduit drops buried in the walls (or surfaced in stores etc). Not in homes though.