How to Strengthen this joist notch?

[jdogg]

Hi all, I have discovered a decentt sized notch in on of my joists, it is a 65mm, 175mm depth joist with about 3m span, I currently have the ceiling down and would like to strengthen it. Could anyone advise the best way to go about this? Thanks

 

[tony1851]

It looks to be fairly near the end of the joist so I shouldn't bother.

 

[jdogg]

It looks to be fairly near the end of the joist so I shouldn't bother.

It is, but the notch itself is about 45mm deep, the plasterboard in front of it had cracked to so I am assuming there must have been a bit of movement?

 

[johnny2007]

If it really bothers you, get a steel plate made and fix it there.

 

[Munroast]

what is it with plumbers? he needed to make a notch for a 15mm pipe not a double decker bus - and then he has nearly missed.

and what has been going on in sparkies brain - 4 large random holes for 4 little cables, then he misses one of the holes and gets two through one

 

[Lower]

I wouldn't bother. That joist is more than up to the job, even with the notch and holes.

Who put the noggins in to support the plasterboard joins? Where they there before or did you put them in? If they were there before, then that might explain the crack if there was a plasterboard joint directly below the notch where the noggin is.

 

[aveatry]

I had somehing simular and cut 2 pieces of 20mm ply to the same size of the joist and glued and screwed it to both sides. Maybe didn't need it but I was replacing the plasterboard and it made me feel better. I also took the opportunity to insulate the pipes

 

[blup]

Should be fine as its near the end of the joist but not at the end

 

[tony1851]

It is, but the notch itself is about 45mm deep, the plasterboard in front of it had cracked to so I am assuming there must have been a bit of movement?

If the notch (45 mm deep?) was near the centre of the span, it would have seriously weakened the beam because usually the bending stress is greatest in the middle, so that's where you need the most material.
The bending stress reduces as you go towards the end, where technically it becomes zero.
But physics doesn't make it easy for us because at the middle of the beam, the shear stress is theoretically zero, but does the opposite of bending stress and increases as you go towards the end of the beam, where it becomes maximum.
But without getting pencil and paper out, I'd say that there's enough depth of beam remaining at your notch to easily accommodate the shear stress.
The only caveat to this is if it is heavily-loaded near the end, such as supporting a bath or h/w tank. If that's the case, you could reinforce it by screwing a length of timber, plywood or steel to the side of the joist at the end, as others have suggested.