Insulating around cables that's running along joists?

[GlanMenai]

Hello, 

 

I'm just starting to think about how to insulate between floors, inside the joists at our property we're renovating. The issue I have is that there's electricity cables running along the inner face of some joists, and at other spots there are electricity cables running through the center of the joists.

 

As I understand, the cables need an air gap around them to perform without overheating - how do people go about insulating in-between the joists if there are cables running along them? In some places, as the cables are spread out and tacked onto the joists, they take about 3/4 of the height of the joist. For the cables that's going through the center of the joists, I imagine I can just put a conduit around these? Some plastic waste pipe of something? 

 

Do people build like a 'false wall' around the cables on the side of the joist, and then insulate from there to the next joist? Or does something like 'Therma Fleece' or 'Rockwool' work ok around cables as it's technically got air pockets in it?

 

One option would of course to insulate with PIR or something underneath the joists, but that brings down the ceiling height, which I'm trying to avoid.

 

Has anyone got any information on this?

Thanks!

[Temp]

The insulation is not likely to be an issue for lighting cables. For power cables there might need to be some derating if this hasn't been taken into account. Typically if you know its going in/undervinsulation you can specify a thicker cable or smaller RCD/MCB but again not always necessary. Remember most power circuits are rings so there are two wires in parallel. Discuss with your electrician.

 

https://professional-electrician.com/technical/impact-thermal-insulation-current-carrying-capacity-flat-twin-earth-cables/

 

In Fig 2, the current-carrying capacity of a 2.5 mm2 flat twin and earth cable is shown in brackets for each of these Installation Methods.

 

 

Edited December 6, 2022 by Temp

[nod]

There’s no issues with using a wool type insulation between joists 

Pretty much as in the loft Cables are buried under at least three layers of insulation