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?

 

[davesparks]

Notching is allowed, but holes are preferable where possible.
I have notched joists in the past for running SWA or 16mm T&E because getting that stuff through holes ain't no fun sometimes.

 

[TJC1]

Out of curiosity why is making notches quicker than say making 2 x 25mm holes using a decent angle drill...?

The install time of cables would be a lot faster!

 

[Zerax]

Having notched and used holes... I reckon, if you're organised, it's far quicker with holes... would be fun to have a race !

A laser level, hole hawg and a combination square would be my weapons of choice.

 

[littlespark]

If you’re feeding through a lot of holes, an apprentice is a good help, guiding the cable in.

 

[LastManOnline]

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?

Notching over holes wins hands down. And laying the cables in rather than pulling through holes in joists is, nt just a great time saver, it's kinder on the cable Insulation. My only problem with it is I don't get to "notch" often enough. Ideally I try to first fix before the upstairs flooring goes down. In agreement with the builder I " notch" the joists where they are resting on a stud or wall. I never do it otherwise. To avoid waking joists
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Notching over holes wins hands down. And laying the cables in rather than pulling through holes in joists is, nt just a great time saver, it's kinder on the cable Insulation. My only problem with it is I don't get to "notch" often enough. Ideally I try to first fix before the upstairs flooring goes down. In agreement with the builder I " notch" the joists where they are resting on a stud or wall. I never do it otherwise. To avoid waking joists

Sorry "weakening"

 

[Mike Johnson]

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.

 

[pc1966]

A hole hawg is a great tool if you don’t have one. Eats through the wood like butter. Get their bits also.

Now I want one! I don't even have any joist-drilling to do, I just want one!

 

[LastManOnline]

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?

 

[Mike Johnson]

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.

 

[DefyG]

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.

 

[davesparks]

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.

 

[Mike Johnson]

@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.

 

[LastManOnline]

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.

 

[davesparks]

This diagram shows the rules quite well

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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.

 

[Mike Johnson]

@ 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?