Loft insulation

[unlucky]

Guys,

Another question, I'm thinking of drilling all the holes for the cable runs on the top floor and getting the cable laid in advance of project re-wire but am worried about the type of cable I need to use.

Im going to be using method 101, clipped to the joists when I am running the cable in the direction of the joist however when I am putting the cable through a joist the reg's state 5cm from either the ceiling or the floor, whichever applies.

So, 5 cm from the ceiling means that when I lay the new insulation ontop of what is already there there will be more than 100mm of insulation surrounding the wires as they pass through the joists (hope this still makes sense) I'm wanting to know the best solution to the problem or am
I worrying about nothing?

I stepped the size of the cable up due to the insulation being laid after the re-wire as is stated in the reg's but am not sure by how much I should de-rate the wire for when it is passing through the joist and the middle of the insulation.

Any help would be much appreciated as always.

Also, do the majority of bathroom fans run off 1.5mm wire or should I be using something bigger to power it from, say, the upstairs ring main?

Thanks to all you helpful people in advance.

Phil

 

[holmslaw]

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[unlucky]

so I would clip to the rafters and then drop the cable down to the ceiling roses?

what about the runs to the switches? these will have to pass through the gaps in the joists so I will come across the same issue won't I?

Thanks for the answer on the fan.

 

[holmslaw]

..

 

[unlucky]

Thanks for the quick response.

Is this the only way round the issue of the loft insulation? If I do clip to the rafters am I OK to just span the rafters when I need to or should it be in any type of conduit?

Thanks again.

 

[holmslaw]

..

 

[Taylortwocities]

You do not want to be drilling holes in joists in a roof space.

Especially new build ones. They are not big enough.

 

[unlucky]

Holmslaw, I know its notifiable but thanks for the warning, I've got a sparky through a couple of refferences that is happy to test and certify my work.

Hes agreed to do three visits, planning it out, after 1st fix then after 2nd fix to test it and sign it off. I've got almost all of it planned out, just a couple of things, like this that I needed to clarify.

Its not a new build but the ceiling joists are not especially deep. So i'll go with the suggestion of battens between the rafters.

Thanks

 

[ColJack]

what is the roof construction?

in older roofs there are often "beams" running at right angled to the ceiling joists that you can clip to.. they are usually about 1/4 the way from the outer walls so are in the space that you can't really use..

you could always run cable tray across the top of the joists, maybe even on spacers to allow for more insulation under the tray..

do us a sketch of your roof space and it's construction and we can advise the best way.