Bad pratice? grooving a joist to pass a cable through.

[PrenticeBoyofDerry]

There must be something in Approved Doc A about it?

 

[JohnW2]

John, That was also my first thought, as I have used that principle myself quite often for top notching. But on the underside there is a distinct danger of stress concentration caused by a notch, whereas on top the notch tends to get pushed together, so I wonder if there isn't a good reason to avoid notching underneath even if the rest of the joist size on its own would be sufficient. No idea really, but maybe worth considering.

Notching on the side opposite the one to which the stress is applied (i.e. notching the bottom of a floor joist) obviously has much more structural effect than notching the side to which the stress is applied - for the sort of reasons you give, but that is obviously taken into account in formal structural calculations.

Kind Regards, John.

 

[JohnW2]

Notching the bottom of a joist can result in the joist splitting along the grain when the joist is bent downwards under loading from the floor it is supporting. A notch in the lower surface has far more potential for weakening or failure of the joist than the same size notch in the upper surface.

Indeed, but models for calculating the de-rating required in both situations exist.

Kind Regards, John.

 

[Ltnman]

This is what I love about this forum. Full of clever people with good advice so thanks everyone. I will not notch the joists now and will think about a plan B

 

[mattylad]

Plan B should be to cut a wider strip in the plaster so that you can get a drill up and drill holes in the joists.

IMO there will be no difference between a thin strip and a wide strip being "smoothed over"....

 

[sparkwright]

Plan B should be to cut a wider strip in the plaster so that you can get a drill up and drill holes in the joists.

IMO there will be no difference between a thin strip and a wide strip being "smoothed over"....

Exactly.

You would be putting back the original piece of plasterboard, and filling this would be just as easy as filling the individual holes. Making the cut out nearer the wall should make the repair less obvious that it being in the middle of the ceiling.