Boarding attic, wires over joists, advice needed.

[cctvtobeornottobe]

Hi there I’m boarding my attic and the wires are going over the joists,

I know I can chisel a grove in the chipboard board or take the wires out of light fixture.

I was just wondering would it be a bad idea just to made a grove in the top of the joist with a round rasp just big enough for the wire to sit in the joist below the board?

I know you can also drill hole in middle of joist just wondering is it a bad thing to make notch in top of joist?

 

[diditrain]

I would say it would depend upon how deep the joists are. They should ideally only be drilled or notched in certain locations. If you google, where to drill joists, you should find plenty of guides. You should consider using safe plates as well, if you go down the notching route.

 

[Lister1987]

You can get attic flooring stilts (around 3-4" in height) - mainly designed to stop compression of insulation fill but it'll also solve the wire issue

 

[Wilko]

Hi - I don’t run twin and earth cables in joist notches due to the risk of damage from a future nail or screw. Here’s an extract of the Electrician’s Guide to Building Regulations on the topic.

 

[Pete999]

Hi - I don’t run twin and earth cables in joist notches due to the risk of damage from a future nail or screw. Here’s an extract of the Electrician’s Guide to Building Regulations on the topic.
View attachment 57818

Are the rules you quote the same for rafters, joists are not the same as roofing trusses are they? just wondering, after all they are not as robust as floor joists. smaller in all planes especially in new houses.

 

[buzzlightyear]

The best way of doing it is to put some plant on timber over the cables, so you do not take the stress out.

 

[radiohead]

Don't notch roof timbers. Either use a proprietary packing device as suggested above or a cheaper solution is to batten off the timbers with some 2x1.

 

[telectrix]

Are te rules you quote the same for rafters, joists are not the same as roofing trusses are they? just wondering, after all they are not as robust as floor joists. smaller in all planes especially in new houses.

good point. i'd be wary of drilling modern roof trusses. the ideal way would be to notch and fit plates. that also means that the cables don't need disconnecting.

 

[Wilko]

Are the rules you quote the same for rafters, joists are not the same as roofing trusses are they? just wondering, after all they are not as robust as floor joists. smaller in all planes especially in new houses.

Hi Pete - I hope you are well .
The minimum depth for unprotected cable should still be 50mm below the surface, but you’re right the strength of the beam needs consideration, which would likely be on a scale of ok to oh dear .

 

[radiohead]

good point. i'd be wary of drilling modern roof trusses. the ideal way would be to notch and fit plates. that also means that the cables don't need disconnecting.

Roof trusses should not be drilled or notched.

 

[Pete999]

Hi Pete - I hope you are well .
The minimum depth for unprotected cable should still be 50mm below the surface, but you’re right the strength of the beam needs consideration, which would likely be on a scale of ok to oh dear .

Yes Mate I'm fine Ta you OK?

 

[pc1966]

A quick search for "safe plate" brings up a range of metal plates you would use to help protect any cables below. I'm not sure quite how much nailing they would take, but at the very least they would show up well on a metal detector if anyone was being diligent before hammering stuff down:

Niglon SAFE PLATE 50 X 100MM - SP3

Niglon SP3 Safe Plate - 50 x 100mm

www.superlecdirect.com

Safe Plate

• Galvanised plate• Used to protect plumbing and electric wiring against random nailing into timber• Quick and easy to install• Width x length

www.toolstation.com

Sabrefix Protecta Safe Plate Galvanised 90mm x 45mm 20 Pack - Screwfix

Order online at Screwfix.com. Galvanised steel plates for protecting wires and pipes. No fixings required. FREE next day delivery available, free collection in 1 minute.

www.screwfix.com

 

[radiohead]

The safe plates I've used are of thick metal and would prevent nail penetration, however I think the important point here is that the OP should not be advised to notch or drill roof timbers under any circumstances. A safe plate would involve notching.

 

[pc1966]

The safe plates I've used are of thick metal and would prevent nail penetration, however I think the important point here is that the OP should not be advised to notch or drill roof timbers under any circumstances. A safe plate would involve notching.

I assumed a safe plate over thin packing material (say 12mm or 19mm thick wood, enough to gap the cables) instead of raising it by the (50mm - floor thickness) ~30mm otherwise needed?
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I agree that they should not notch the beams!

 

[jdinduntocher]

I recently did my attic which had 16 mm conduit running over the joists I used 38x19mm roofing batons and put them on top of existing joists leaving a gap where the conduit crossed a joist this saves you trying to reroute cables and just screw them in place.It may be more expensive but it will save loads of time jd