Routing of lighting circuit in Loft

[00db]

Can anyone please advise if it is acceptable to run a lighting circuit cable between Rafter Insulation Board and the Sarking Felt (1960s Bitumen type)?

I have installed 75mm Ecotherm board between the rafters (which are standard 100mm) leaving a 25mm gap. I am considering running a 1.5mm cable up through this gap to get my circuit from one side of the loft to the other and to allow a light to be installed at the ridge.

Would this leave the cable to unacceptable levels of cold during winter and heat during summer?

 

[PrenticeBoyofDerry]

Can you not clip the cable to the rafters, locating the cables around the middle 50mm or even surface mount the cable in trunking.
They will be no actual requirement that states what you intend to do is non-compliant.
But the requirements concerning external influences, may lead you to consider a better method of install.

 

[00db]

If I were to clip the cables to the rafters I would have to bury the cables inside the insulation board? I plan to plasterboard over the rafters eventually to create a sealed loft room so trunking may look unsightly. Thanks for the response, I am going to get a local sparky out to take a look I think.

 

[Iggifer]

can you not go under the floorboards?

 

[dhutch]

If I were to clip the cables to the rafters I would have to bury the cables inside the insulation board?

I know you cant have PVC against EPS but otherwise, assuming the cables spec'ed for it is that not ok? Conduit?

 

[Scoby_Beasley]

EPS

EPS? Having a blond moment!!!

 

[Iggifer]

expanded polystyrene insulation?

 

[dhutch]

expanded polystyrene insulation?

Yes, sorry. As aposed to polyurethane.

 

[PrenticeBoyofDerry]

If I were to clip the cables to the rafters I would have to bury the cables inside the insulation board? I plan to plasterboard over the rafters eventually to create a sealed loft room so trunking may look unsightly. Thanks for the response, I am going to get a local sparky out to take a look I think.

There is not a problem with burring the cables, that is quite common.
Other thing to consider is RCD protection of cables that are within walls less than 50mm, if they are not surface mounted. This may not apply to the void within the rafters but would for switch drops.

 

[Scoby_Beasley]

Could you not run a channel in the insulation on one rafter a.k.a:

 

[ban-all-sheds]

I have installed 75mm Ecotherm board between the rafters (which are standard 100mm) leaving a 25mm gap.

I plan to plasterboard over the rafters eventually to create a sealed loft room.

This seems like a lot of work to do for cosmetic reasons, so it's reasonable to assume that you are doing it so that the loft can be heated.

1. Will that amount of insulation provide the amount of insulation required by the Building Regulations?
   
2. Will the floor support the weight of whatever activities go on up there?
   
3. What will you do to ensure vapour-tightness of the layer between the heated loft and the unheated gap below the tiles? Poking holes in it for cables is not a good start, nor is leaving any gaps at the eaves.