Notching timbers instead of drilling....

[TJC1]

Good morning all

Is there any reg to say about drilling cables into joists instead of notching?

I have been an electrician for 12 years now and have always drilled out timbers, we are starting a HUGGGGGGGGGGE rewire with long runs. It would save a lot of time i think to notch the top of the timbers and use a protective metal plate to go over after the install

Thoughts?

 

[LastManOnline]

@DefyG Sounds like you are just making an excuse to do whatever you want, rather than what is correct or safe, is that how you think of your electrical work.

@DefyG Sounds like you are just making an excuse to do whatever you want, rather than what is correct or safe, is that how you think of your electrical work.

Mike I find your conclusion there a little odd. I, m not on here making excuses for "whatever I want". Firstly, notches are allowed. Secondly if you are going to notch, would, nt it be common sense to do it at a point where the joist has rock solid support? or do you think notching a joist where it is freestanding is a better idea?

 

[Mike Johnson]

Read the post it was not aimed at you the clue is at the beginning.

 

[LastManOnline]

@ Edmond I hope I have misunderstood your above comment, drill a hole, cut down to it, lay in the cable and then put the bit back?

No Mike. You did, nt understand a jot of what I said.
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No Mike. You did, nt understand a jot of what I said.

Apologies Mike. It's clearly past my bedtime

 

[Mike Johnson]

.

 

[davesparks]

Mike I find your conclusion there a little odd. I, m not on here making excuses for "whatever I want". Firstly, notches are allowed. Secondly if you are going to notch, would, nt it be common sense to do it at a point where the joist has rock solid support? or do you think notching a joist where it is freestanding is a better idea?

No thinning the joist at the point where it is supported is not a good idea at all.

It is common sense to do it at the point prescribed in the building regulations which is where engineers have worked out it is safe to do so.

 

[DefyG]

@DefyG Sounds like you are just making an excuse to do whatever you want, rather than what is correct or safe, is that how you think of your electrical work.

????? I was merely pointing out what joists of a lot of older properties are like after many years of work and re-work and that to try and calculate the strength of such timbers would be 'impossible'! .......

 

[Mike Johnson]

@Edmond just follow the guide lines posted by davesparks above and you wont go wrong.

 

[LastManOnline]

No thinning the joist at the point where it is supported is not a good idea at all.

It is common sense to do it at the point prescribed in the building regulations which is where engineers have worked out it is safe to do so.

"thinning the joist at the point where it is SUPPORTED is not a good idea at all". Classic
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@Edmond just follow the guide lines posted by davesparks above and you wont go wrong.

Thanks Mike.
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No thinning the joist at the point where it is supported is not a good idea at all.

It is common sense to do it at the point prescribed in the building regulations which is where engineers have worked out it is safe to do so.

No thinning the joist at the point where it is supported is not a good idea at all.

It is common sense to do it at the point prescribed in the building regulations which is where engineers have worked out it is safe to do so.

DAVE, you made a very valid point earlier about electricians using their intelligence. Whichever engineer worked out that it is safer to slot a joist where it an sag rather than where it can be supported, well.......

 

[Mike Johnson]

End bearings, maximum compression and no help from continuous fibres.

 

[littlespark]

I can see the logic. You don’t want to thin the joist at the point where the wall is pushing up on it.

 

[davesparks]

DAVE, you made a very valid point earlier about electricians using their intelligence. Whichever engineer worked out that it is safer to slot a joist where it an sag rather than where it can be supported, well.......

Yes, have you studied the stress diagrams for beams?
Have you considered what the effect on the strength of the joist will be by thinning it at the point where it is supported?

Have you ever noticed how splits in timber tend to start where someone has cut through the fibres of the grain?

I learned a lot of this stuff from my father who was highly qualified in structural and building work and a very well respected building control officer.

If you look at the actual stress patterns, areas of tension and compression etc in a joist you can remove much of the middle of the joist at 1/3 of the span leaving a relatively small amount of the top and the bottom of the joist with minimal effect on its strength, but a hole drilled through the centre at the end or middle of the span can have a much bigger affect on its strength.

 

[Mike Johnson]

Just think of Castellated beams to get the idea, but note the shear webs near the bearing points.

 

[LastManOnline]

Yes, have you studied the stress diagrams for beams?
Have you considered what the effect on the strength of the joist will be by thinning it at the point where it is supported?

Have you ever noticed how splits in timber tend to start where someone has cut through the fibres of the grain?

I learned a lot of this stuff from my father who was highly qualified in structural and building work and a very well respected building control officer.

If you look at the actual stress patterns, areas of tension and compression etc in a joist you can remove much of the middle of the joist at 1/3 of the span leaving a relatively small amount of the top and the bottom of the joist with minimal effect on its strength, but a hole drilled through the centre at the end or middle of the span can have a much bigger affect on its strength.

That is a persuasive post and one I will not ignore