Can I drill this joist?

[Lamentable]

Please take a look at this diagram which shows the joists under the floor of a 1st floor. The room is partly over a hall, and partly over a garage hence the brick walls below.

I need to get 2 bundles of comms cables through this location, both around 25mm in diameter (see red text on diagram).

The joist runs off the landing, where I presume it is supported by the newel posts. I don't know exactly where it finishes in the room, but definitely on or after the 3rd crossing joist looking from the top to the bottom of the diagram.

Someone has already notched it a couple of times and drilled a really bad hole through the joist at around 45 deg. from near the top to the bottom as you can see on the diagram. I can use this hole for one bundle, maybe, the angle may give an unacceptable bending radius on the cat 6 once the floor boards on back on.

My questions:

1. Is it safe to put in another hole near to this one that has been drilled badly ?

2. Could I sister the joist to provide more strength on it's run along the landing?

3. Could I notch out and fill the badly drilled hole and then sister allowing me to drill two new holes within regs? Or sister then notch out? I would be removing probably around 150mm of the depth of the 170mm joist to do this.

4. Could I bond some 18mm ply side on and put the hole in anyway?

I'm open to ideas, as I don't have another route for the cables at this time.

Thanks in advance.

 

[Wayners]

Watch this.
Holes drilled and joists strengthened.
Will help to understand what you need to do. Hopefully...

 

[robinbanks]

Glue and screw two full length (as much as you can get in between the adjacent perpendicular joists) strips of 18mm structural ply that are the full depth of the joist, to the joist sides, such that the existing 25mm 45degree hole and notches are covered. Put your other 25mm holes anywhere convenient on or near the joist centre line that is not within 75mm of the diagonal hole, a notch or within 75mm of each other
These numbers are conservative and youre unlikely to see any ill effects from flexing them slightly if needed. You could also consider unbundling your cables and pass through this joist in more places with smaller holes, or pass around the damaged area by going north, west then south per your diagram