Loft wiring

[rob3000]

Hi

I want to insulate and board out my loft, but when it was originally wired all of the cables have been run (and clipped) over the top of the joists.  I am assuming that the only way to get around this problem is to disconnect one end of the cable, drill through the joists and re-connect.  Is there any other way? Is it ok to drill through joists, are there certain rules to follow when doing this?

 

[SLIPSHOD & SLAPDASH]

Usually the joists in a loft are smaller and i was taught not to drill them. Can the cables be pulled over to  corners/cross braces.

 

[rob3000]

There might be a couple that could be re-routed, but most run a pretty direct route from one point to another straight over the top of joists with not much slack.  I only want to put a few boards down, I didn't really want to get into replacing cables!!!

 

[Davethsparky]

Roof timbers, including the ceiling collars should not be drilled or notched. When a floor joist's size is calculated an allowance is factored in to the calculation for service holes to be made, this is not done with roof timbers as there is no logical need for service holes.

also the stresses applied to the timbers are different in a joist to a ceiling collar so holes will affect them differently.

 

[rob3000]

That seems sensible.  So how are cables run when a house is re-wired or an extra socket on the opposite side of the room is needed?  Does everything run round the outside so no drilling is needed?

 

[Davethsparky]

That seems sensible.  So how are cables run when a house is re-wired or an extra socket on the opposite side of the room is needed?  Does everything run round the outside so no drilling is needed?

Thats a very open question! Sockets are normally cabled under the floors of a room, so drilled through the joist's, and cables in a loft would be run on top of the ceiling collars and hopefully clipped 

 

[SLIPSHOD & SLAPDASH]

Notch the new floor to miss the cables, that would also show  where they are. All it needs us a 10mm wide notch so should not be any problems with things falling through or damaging the cables

 

[ProDave]

Lay battens along the top pf the ceiling joists before you put the floor down, leaving gaps where the cables are.

You can also buy plastic chairs that clip to the top of the joists and support the floor panels above the joists, handy if you have thick insulation that sticks out above the joists.

 

[Andy™]

if you board straight onto the joist you wont get much insulation under there. general guidelines are 250-300mm, your joist will be less than half of this. prodave suggestion above will work and give you a bit more space, alternatively you can install some new joists the opposite way which will give you more space for insulation and get rid of the cable issues, however its not a good idea to have the cables fully surrounded in insulation. lights will most likely be OK, shower and sockets etc wont. you might end up with melted cables, or a fire

 

[steptoe]

I done my loft a short while ago,

 

[Andy™]

typical sparky. good woodwork, ****e electrical work

 

[steptoe]

typical sparky. good woodwork, ****e electrical work

:slap

 

[Sharpend]

You might want to call our good friend r b in to sort that nest at the gable end! 

 

[Richard-the-Ninth]

Can your joists support the extra weight of all the additional timber, and what ever it is you are going to put up there?

 

[Rob_the_rich]

Is it only the thinner lighting cables you have in your loft? or are there other thicker ones? just worried about them overheating if covered with insulation, lighting ones are usually fine.

 

[Rob_the_rich]

I done my loft a short while ago,

Is it my eyes or is it not level? Do the empties end up rolling off one side? :innocent

 

[steptoe]

Is it my eyes or is it not level? Do the empties end up rolling off one side? :innocent

I see what you mean,

Half cut photographer,!? :C

If you look carefully you can see the string levels at each side. 

 

[Andy™]

strings for level? oops. i thought that was the internal phone system

 

[Blue Duck]

@steptoe

plenty of room for the storage of mumified bodies

 

[Sidewinder]

Almost all horizontal structural members can be "drilled through", if, this is done correctly.

Yes it is allowed in the building regulations.

Yes there are some that are not, which is why I put "almost" above.

IF you drill through on the neutral axis and the hole is perpendicular to the member, and the material removed is such that it falls within that allowable for the loading on the member, then all is fine.