cable run perpendicular to loft joists.

[ianphilip007]

hi just been to look at a job, have to get a cable accross 4 joists ( perpendicular) now i know drilling loft joists is a no no, the cable run will be in an area of the loft not used for storage and the customer has no intention to board out the loft is there anything wrong with laying the cables accross the joists, neatly and secured under the existing insulation? ( 1.5mm 6amp lighting)

 

[i=p/u]

see it all the time, and you can drill the joists???????????/

 

[ianphilip007]

can you ?? always wondered why people say you cant as they support my weight when im waliking arround lofts.

 

[i=p/u]

0.4 times the span = dont drill loads of holes beside eachother and leave spaces of hole diameter.... its in a boook somewhere

 

[ianphilip007]

is this another myth

 

[Octopus]

How is a single 10mm hole going to weaken a joist?

That said some of the new builds around here have joists I wouldn't burn!

 

[ianphilip007]

yes i know its in the book is that for floor and loft joists ?? im not totally sure it is. i guess it depends on the size of the joist in the loft space.

i cant really see any problem with laying over the joist as in a non traffic area and customer is not boarding the loft

 

[ianphilip007]

i agree murdoch as i said if the joist can take my weight i cant see how a 10mm holw is going to make the roof come crashing down.

 

[i=p/u]

ive seen it loads of times, but you should clip to the joists slightly below the top surface, just so no1 does kick them stand on them

 

[Octopus]

I'd venture to suggest that going through the odd joist is better, especially if some muppet comes along with boards later and traps the cable between the joist and the board!

 

[i=p/u]

yh put them in joists if only four joists and one cable = 10mm hole be fine

 

[ianphilip007]

thats my preferred option to be honhest just wasnt sure just looked in the building regs for electricians and it states the hole/span sizes are for both roof and floor joist i guess its wheather a roof joist = loft joist. confusing

 

[HandySparks]

If it's a modern roof with thin factory-made trusses, I wouldn't drill holes in them; they're not designed with much excess load capacity.

 

[gedster]

You can drill joists but not near joist ends.

 

[somersetsparks]

Why not just cross the joists at a convenient point, e.g. in the eaves? most people don;t bother boarding that far down and it saves drilling joists

 

[MarkieSparkie]

Notching and/or drilling ceiling and floor joists are both allowed under the Building Regulations Part A.
Notching joists in top edge only, in the zone 0.07 to 0.25 of the span, maximum size 0.125 x depth of joist.
Drilling joists on the centre line only, in the zone 0.25 to 0.4 of the span, maximum size 0.25 x depth of joist, holes in the same joist should be at least 3 diameters apart.
No notches or holes should be cut into roof rafters, other than at supports where the rafter may be birdsmouthed to a depth not exceeding 0.33 x rafter depth.
See EGBR 2.3.2 and 10.1.1 for details.

 

[DaveyD]

Can you not put into trunking and clip out the way under the eves. Even if boarded it can butt up to the trunking.
That's what I do.