Running lighting circuits in the loft space.

[Amp David]

When running lighting cables in the loft space, they can be clipped to the side of the joists no problem. When the cable then needs to be run at right angles to the joists, is it best pratice to drill the joists to pass the cable through or run over the top of them.

Cheers for the advice guys.

 

[pushrod]

If you want to drill joists the holes should be centred and no more than 0.25 the depth of the joist in diameter. They should be positioned in the zone between 0.25 to 0.4 of the span from either end. (Regulation 522-12-03 of BS 7671) LINK

 

[chris murphy]

If you want to drill joists the holes should be centred and no more than 0.25 the depth of the joist in diameter. They should be positioned in the zone between 0.25 to 0.4 of the span from either end. (Regulation 522-12-03 of BS 7671) LINK

"Hello pushrod"


Without going to look at the British Standard or the Regulation that You have quoted I am fairly sure that what You quoted applies only to Floor Joists.

Even then Joists of less than 200mm [8"] should NOT be Drilled or Notched without additional reinforcement being applied to the Joists - for example 18 / 20 mm [3/4"] Ply being Laminated onto the sides of the Joists.

An example of NOT Drilling or Notching Joists of less than 200mm [8"] Deep is that Ground Floor Joists which are usually only about 100mm [4"] - as You know these should NEVER be Notched or Drilled - Even though these Joists will be supported on Wooden Plates and Brick Piers at regular intervals.

So although these 100mm / 4" Joists are well supported they should NOT be Drilled or Notched - It follows that a similar size Ceiling Joist which is only supported on the Room Walls [If Then] should NEVER be Drilled or Notched.

Ceiling `Joists` are usually part of the Roof Truss construction as was mentioned in previous Posts - So to ensure that the Roof Structure is NOT compromised under NO Circumstances should they be Drilled for Cables or Pipes.

Apart from weakening them in relation to the Roof Structure they would also be weakened with regard to walking across them when People have to access the Loft.

I have actually seen Ceiling Joists with Drill Holes in them for cables - the Homeowner had told the Electrician that they were going to Board Out the Loft Space - So the Electrician Drilled 25mm Holes right across the Loft - In the MIDDLE of the Span between the outside wall and the internal walls - to be close to the Room Lights in the Centre of the Rooms !

Imagine that on Ceiling Joists that were only 95mm X 47 mm [3 3/4" X 1 7/8"] !

Luckily I saw this as I am a fairly Big Man - I might well have been heavy enough to have these Drilled Ceiling Joists Break under My Weight !


Chris


P.S. - I am NOT `being funny` about noting the Metric and Imperial Measurements - the Imperial are what the Joists actually Measured - the Sizes of Wood that were used at the Time of Construction of the Houses.

 

[ackbarthestar]

The last couple of loft extensions were more or less top floor rewires where I ran and clipped the cables to the joists and then only hopped over the joist in the eves, never over the joists in the middle of the loft.
Another one was where there was a known extention going to be fitted at a later stage so ran the cables to the end of the joists and then clipped them up on the purlings so the cables were accessible and easy to move around while building work took place.

I was trained never to drill joists in the loft, particularly A framed structures, since they are not designed to carry the weight of a floor unless its a Victorian house where they are usually boarded out anyway.

edit: Generally as a ROT, any joist under 5" (125mm *50mm) should not be drilled.

Legh

 

[Engineer54]

Going by most of what you've been saying above, it's a wonder most of the houses over the years haven't collapsed on themselves.

Funny how all this this waffle was never thought of, or required in the past. Mind you, the older houses were made and built to last!! Can't see a lot of these modern homes passing the test of Time!! lol!!!

Most of these new rules (to me anyway) are just a load of hot air, dreamt up by those that have nothing better to do!! It would surprise me, if an electrician needed to drill a hole for cables to pass in a floor joist, it Will be drilled, and the cables will pass through that joist!! Come to that if a plumber needed to notch a joist for his pipework, it's going to get notched. ...It's the way of the World!! lol!!

 

[ackbarthestar]

- E54, You'll see holes and notches through most joists in older houses, but not, generally, in the loft !

 

[Engineer54]

- E54, You'll see holes and notches through most joists in older houses, but not, generally, in the loft !

Read my post again, did i say or mention loft joists?? Some of those older houses have loft joists, at least as big if not bigger in some cases than it's floor joists!! lol!!!

 

[ackbarthestar]

Read my post again, did i say or mention loft joists?? Some of those older houses have loft joists, at least as big if not bigger in some cases than it's floor joists!! lol!!!

I did, and you applied your argument generically whether drilled or notched, leaving it open !

edit: Plumbers don't usually notch or drill joists in loft spaces, unless they are bonkers

 

[ipf]

Once came across a situ where a loft joist had a 5'' complete cut out to allow the install of a recessed fitting. To make matters worse, a repeat on the same joist a couple of yards away. Probably even have had the mice cr****n' 'emselves.

 

[Engineer54]

I did, and you applied your argument generically whether drilled or notched, leaving it open !

edit: Plumbers don't usually notch or drill joists in loft spaces, unless they are bonkers

But i wasn't referring to your post, ...just that i'm not that quick at typing as most!!

How many plumbers do you know, ...that aren't Bonkers?? lol!!!

 

[chris murphy]

But i wasn't referring to your post, ...just that i'm not that quick at typing as most!!

How many plumbers do you know, ...that aren't Bonkers?? lol!!!

"Hello Engineer54",


I realise that You are Joking about Plumbers being Bonkers - words to that effect - But I have often seen references to Plumbers [Sometimes meaning Heating Installers / Engineers] that were less than Complimentary on the Forum.

I have definitely noticed that this does NOT seem to happen on Plumbers Forums regarding Electricians being even `Mildly Insulted`/ Refereed to in a less than Complimentary way.

Do You happen to know WHY this `Insult Plumbers` theme seems to happen on here ?

I am NOT being Over Sensitive here - I would definitely NOT take these comments seriously - I just wondered WHY they seem to be made so often ?

Having started My Career with a Plumbing Apprenticeship and then continued with further Training and Exams in Heating & Ventilation - Gas Utilisation - Electrical Installation - Defined Scope for Gas Installers / Heating Engineers etc. I am Certain that the Extent / Content / Time Scale of Training and Exams that I have taken is At Least Equal to MOST of the Electricians on here.

So I would state that I am in NO Way a Tradesman / Engineer with `Lesser Training` in MY Industry than an Electrician has in theirs.

I realise that the Electrical Trade / Industry is a Highly Technical Trade / Industry.

I wonder Why is it that some Electricians SEEM to be intimating that Plumbing / Plumbers [inc. Heating Engineers / Installers] are somehow in a `Less Technical Trade` / Industry ?

Some of the comments that I have read on the Forum seem to be directed at `Plumbers` [although the topic might be about Central Heating] as being somehow `Inferior Tradesmen` - Or that Plumbing [inc. Heating ?] is a `Lesser Trade` - ?

I definitely don`t want this to start a Row - I am just Intrigued about the comments that I have seen on here about Plumbers.


Regards,

Chris

 

[telectrix]

1910 terrace, they're only 3 1/4" x 2 1/4".

Think it would be best to take them to the edge before running the m accross the loft.

Thanks for the advice.

in an old house with a proper roof support structure as opposed to the modern trusses, the ceiling joists are there solely to support the ceiling. these can be drilled sendibly without affecting the strength of the structure. however, i consider it good practice to route the cables towards the eaves when running at right angles to the joists. they are also then out of the way of mr. joe public's size 10's.

 

[mackers]

as said if trusses DO NOT DRILL . also as said try keep away from areas likley to be used for storage/access. also bare in mind loft insulation as this has a great detrement to the cable loadings. to be fare in the 20 + years i been a spark can,t remember joist been drilled in any loft ive been in ,most are 3x2 unless designed for dormers.
only time i drilled a truss was when i was an apprentice and got the mother of all -------ings LOL

 

[Dan the spark]

Wouldn't advise drilling the joists in a loft, just run the cables where no one is gonna tread or put things on:builder:

 

[Deleted member 26818]

The joist in lofts, are there as far as I'm aware, to fix the ceiling to.
They are not generally structural.
Yes crtain pre-formed trusses are structural, and it may not be possible to drill those.
I would would suggest contacting either building control or a structural engineer in such circumstances.
Remember, that cables if run through joists should be at leat 50mm from the surface of the ceiling or floor, or provided with mechanical protection.

 

[Specialist]

Long time since I studied this, but I think you'll find that the the Loft joists make up part of the Structural Integrity of the roof & holding the ceiling up is secondary.
The Trusses (Rafters) & ceiling joists make up an A frame structure, what happens when you remove the crossbar from an A frame & then load weight onto it ? It collapses.