Discuss Notching timbers instead of drilling.... in the Electrical Forum area at ElectriciansForums.net

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From a structural point of view drilling holes in the neutral zone of the joint is preferable i.e. in the centre of the joist between the tension and compression area, notching reduce's the compression area of the joist which is its major work zone.
Does that still apply if you have notched over a stud or wall and by that I mean the notch is sitting middle of the wall?
 
Yes, makes no difference especially if the stud or wall are a structural support member and you have reduced the end bearing of the joist.
 
The existing joists are probably already peppered with holes and notches form previous installation and plumbing, and not always in the zones indicated in the OSG, so god knows how one is ever to calculate what strength any joist has left!
The maths might work for a new joists but 100+ year old properties ....! especially where irregular (oak) beams have been used.
 
Does that still apply if you have notched over a stud or wall and by that I mean the notch is sitting middle of the wall?

Notching the joist where it sits on a wall is not permitted in building regulations as far as I know.
There are specific places where notches are permitted and limits to their size.

Holes are ideally placed at 1/3 the span of the joist, on the centreline and subject to size and spacing limits. From memory holes are permitted between 0.25 and 0.4 of the span in building regulations, must be spaced by at least 3x the diameter of the largest hole, can't remeber the limit of diameter but it is related to the depth of the joist.
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The existing joists are probably already peppered with holes and notches form previous installation and plumbing, and not always in the zones indicated in the OSG, so god knows how one is ever to calculate what strength any joist has left!
The maths might work for a new joists but 100+ year old properties ....! especially where irregular (oak) beams have been used.

Older properties had the joists oversized to allow for service holes to be cut out.
It's more modern builds where joist sizes can be calculated down to a minimum (cheapest) permitted size that the rules on hole locations become more important.
 
Yes, makes no difference especially if the stud or wall are a structural support member and you have reduced the end bearing of the joist.
Then I bow to your greater expertise on this one. In practice we would actually drill a hole first, then slot. After laying in the cables, reinsert the cut out slot and leave a neat and tidy job behind.
 
This diagram shows the rules quite well

Notching timbers instead of drilling.... upload_2019-4-8_14-46-14 - EletriciansForums.net
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Then I bow to your greater expertise on this one. In practice we would actually drill a hole first, then slot. After laying in the cables, reinsert the cut out slot and leave a neat and tidy job behind.

What's the point in putting the cutout bit back in?

Notches for cables should have metal plates fitted to prevent nails or screws penetrating.
 
@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 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 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'! .......
 
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.......
 
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