cable run perpendicular to loft joists.

[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.