T&E routing in insulated wall

[richeighty1]

Good evening,

we are currently in the process of renovating the kitchen in our granite cottage which has necessitated the removal of much of the existing dry lining. I am now in the process of replacing this and upgrading the insulation and would like some guidance on routing the ring within this.

The previous occupants electrician had clipped the 2.5mm T&E for the kitchen/utility room ring directly to the external granite walls. This was the covered with XPS backed plasterboard dot and dabbed to the exterior granite. The cables essentially ran in the 20 - 40 mm airgap (variant as the walls aren't flat) behind the plasterboard.

We will be relining the walls using 50mm Kooltherm between 75 x 50 studs, with a 25mm airgap at the rear. Practically, without wanting to run the wires through the insulation, the two options I can see are to stick with the existing method and have the wiring clipped to the exterior wall in the airgap, or to notch out the front face of the insulation and clip directly to the studs. The wires run down from a service void at the top of the wall. Currently the ring is protected by a 32A MCB. Hopefully the sketch below shows what I'm on about...

My concern with option 1 is that it necessitates running the wires through the insulation to reach sockets etc, and with option 2 it is the later danger of screws / fixings running into the cable either when fixing the plasterboard, or more likely in 3 years time when the wife wants a picture moving...

Any thoughts / suggestions would be appreciated.

Many thanks.

 

[ban-all-sheds]

My concern with option 1 is that it necessitates running the wires through the insulation to reach sockets etc,

Are you planning on having all your sockets & switches etc surface mounted or recessed? If the latter then you've already got a lot of work to do to ensure that you maintain an intact vapour control layer - a few cables coming into the box won't really make any difference to that.

If you're going for surface mounted accessories because of the VCL issue then yes, you will have to deal with the fact that the cables will be compromising it.

and with option 2 it is the later danger of screws / fixings running into the cable either when fixing the plasterboard, or more likely in 3 years time when the wife wants a picture moving...

That shouldn't be a problem - I assume you do intend to comply with what the Wiring Regulations say about where concealed cables may be run?

//www.diynot.com/wiki/Electrics:walls

What will be a problem is that you will have removed the VCL from the insulation board, as you show in your sketch:

 

[richeighty1]

Hi, thanks for your input.

My concern with option 1 is that it necessitates running the wires through the insulation to reach sockets etc,

Are you planning on having all your sockets & switches etc surface mounted or recessed? If the latter then you've already got a lot of work to do to ensure that you maintain an intact vapour control layer - a few cables coming into the box won't really make any difference to that.

Unfortunately, due to aesthetics, it will be the latter.

If you're going for surface mounted accessories because of the VCL issue then yes, you will have to deal with the fact that the cables will be compromising it.

and with option 2 it is the later danger of screws / fixings running into the cable either when fixing the plasterboard, or more likely in 3 years time when the wife wants a picture moving...

That shouldn't be a problem - I assume you do intend to comply with what the Wiring Regulations say about where concealed cables may be run?

//www.diynot.com/wiki/Electrics:walls

Yes, I had checked what was acceptable in terms of the path that cables should take and was aware of this part of the regulations and was intending on complying with them. To do so, the second option would either necessitate having my sockets on 400mm centres or adding additional studding to run my cables down.

What will be a problem is that you will have removed the VCL from the insulation board, as you show in your sketch:

In that case would the inclusion of a 500 gauge polythene sheet between the plasterboard and the studs / insulation be a suitable solution, given that I will have to work to maintain the VCL, regardless?

Am I correct in believing that the second option would be in accordance with reference method 102 (excuse my poor wording)? And how would running the cable through the insulation into the socket (option1) downgrade its current carrying capacity - am I correct in being conservative and saying that as it would be enclosed in insulation for part of it's run then the capacity would drop to 13A per 103?

Many thanks again for any assistance.

 

[ban-all-sheds]

To do so, the second option would either necessitate having my sockets on 400mm centres or adding additional studding to run my cables down.

Why?

In that case would the inclusion of a 500 gauge polythene sheet between the plasterboard and the studs / insulation be a suitable solution, given that I will have to work to maintain the VCL, regardless?

How would you seal that, particularly in the cavities behind the accessories?

Am I correct in believing that the second option would be in accordance with reference method 102

Yes.

And how would running the cable through the insulation into the socket (option1) downgrade its current carrying capacity - am I correct in being conservative and saying that as it would be enclosed in insulation for part of it's run then the capacity would drop to 13A per 103?

No:

 

[richeighty1]

And how would running the cable through the insulation into the socket (option1) downgrade its current carrying capacity - am I correct in being conservative and saying that as it would be enclosed in insulation for part of it's run then the capacity would drop to 13A per 103?

No:

Excellent, thank you for that.

Change of plan. If I increase the depth of the studs relative to the thickness of the insulation to create a void behind the plasterboard, I will have a space sufficient space to run cables and recess the socket boxes without penetrating the VCL. To do this I could either increase the depth of the 75mm studs or keep the existing 75mm, tack over a 500 gauge sheet (which may be superfluous)and then attach 25mm x 50mm to create the void. Poor (rather rushed) sketch:

 

[JohnW2]

Change of plan. If I increase the depth of the studs relative to the thickness of the insulation to create a void behind the plasterboard, I will have a space sufficient space to run cables and recess the socket boxes without penetrating the VCL.

You could, but it seems a bit much to have to modify the wall in order to facilitate installation of sockets and cables. You are far from being the first person to encounter this issue, and I would doubt that many have gone to the lengths which you suggest.

Kind Regards, John