House rewire-loft wiring & insulation

[u0362565]

Hi all,

We want to get our house rewired and have been told that wiring in the loft will be left loose sat on top of insulation. Unless we remove the insulation ourselves then the wires can be secured to I assume sides of joists. The old wiring is clipped to the sides of joists now and through drilled holes through the joists.

What is the best practice on this? To me the secured and clipped approach seems better and I don't want a 'less good job' in this respect compared to what was there.

I'm willing to pull the insulation out temporarily, glass and rock wool if it's worth it, thankless task that it is.

We may floor the loft later if this makes any difference to the wiring position re clipping Vs loose.

Thanks for the advice.

 

[HappyHippyDad]

It would be absolutely horrible to have all the cables scattered over the top of the insulation. Also, it would make it extremely difficult, probably impossible to board, as the cables would be on top of the joists.

A good electrician will know ways around this. Reusing existing holes (I personally wouldn't make any in small loft joists), running cables around the edge, fixing another piece of wood on top of the joists to run cables along, so that loft boards can slot up against it etc etc.

Insulation is horrible to work with though, and if it was double layered I would certainly be adding on quite a sum to be rolling it all up neatly and then relaying.

 

[u0362565]

Thanks for the comments.
They said they'd try to keep it straight and tidy and supported where possible and bunch cables together, but did mention wiring on top of insulation and that they wouldn't remove any insulation. There are two layers I think it's either 230 or 270mm in total with the second layer being on top of the joists except where exposed to walk on.

It sounds to me like it's most likely to be done best if the insulation were removed. But if I were to relay who knows where I'd store it in mean time.

 

[littlespark]

There is an issue if the cables were to end up being buried under the insulation. Derating factors have to be applied, and would mean the circuit breaker may have to be downsized or cable size increased to comply with regulations.

 

[u0362565]

I see, that potentially only complicates matters. Most lofts have insulation these days so there must be guidelines as to where to put wires in relation to it.

It sounds like above it and still accessible is ideal from an electricians point of view.

 

[newfutile]

We used to do loft conversions and they always used to use bigger joist running 90 degrees to the originals, notches were cut for cables and other services

 

[pirate]

I like the cables away from the loft floor/insulation as much as possible, especially if flooring might be installed.
On one job I attached timber battens along the sloping roof-timbers, about a metre above floor level, from end to end of the loft, both sides and attached all wiring to those battens, with cable drops fastened down the roof timbers and to the floors below. This meant the cables were visible, accessible and clipped direct for most of the runs. I'd have used tray instead of battens but the budget didn't run to that and there were plenty of wooden battens on hand. Another advantage of this system is of course that it is easy to label each cable for clear identification in the future, without having to lift insulation and try to trace which cable does what.

 

[westward10]

Just tell them you do not want it slung across the insulation.

 

[u0362565]

I like the cables away from the loft floor/insulation as much as possible, especially if flooring might be installed.
On one job I attached timber battens along the sloping roof-timbers, about a metre above floor level, from end to end of the loft, both sides and attached all wiring to those battens, with cable drops fastened down the roof timbers and to the floors below. This meant the cables were visible, accessible and clipped direct for most of the runs. I'd have used tray instead of battens but the budget didn't run to that and there were plenty of wooden battens on hand. Another advantage of this system is of course that it is easy to label each cable for clear identification in the future, without having to lift insulation and try to trace which cable does what.

Yes I think I know what you mean, almost like guttering running along the outside of the house but used to run the cables. At some point though you have to drop the cables for say bedroom light fittings so you need a route through flooring/insulation. We're having down lights in the bedrooms so that makes it maybe more awkward than a single pendent where you have one point per room where insulation needs to be clear. I guess we don't know exactly what we will have in future, how much flooring etc so it's really a best guess as to what to do in the interim with the loose fill insulation. Part of me thinks just have plenty of length on the cables so if they need to be rerouted later there is slack to do so. But it might be that's not allowed.

 

[u0362565]

Just tell them you do not want it slung across the insulation.

With the alternative being? I was thinking initially maybe I could selectively lift insulation where the current wires run to avoid lifting it all but the wires are quite wide spread and I don't know exactly where they need to get to to run the new wiring.

 

[pirate]

The wiring drops will be mostly vertical, through the insulation. Especially for LED lighting I wouldn't be bothered about derating a cable over its entire length if 6" went through the insulation.

 

[oscar21]

90% of houses will have had insulation fitted after the wiring was done in the loft, then more insulation on top of it over the years. I know about derating factors etc but in all my time working in the domestic sector I've never come across an overheating lighitng cable in a loft, and that was when it was all fillament lamps, personally with most lighting LED now I see it as a none issue. I did once see a piece of 1mm cable that had slight signs of overheating but still seemed to work ok but that was when it was looped to two single ovens in a kitchen.

Personally I shy away from occupied rewires nowadays and the rediculous amount of loft insulation I have to contend with is one of the main reasons why. Sometimes if its been put down neatly you can roll it up out of the way and do the wiring but I would never leave the cables loose in a loft and if I was doing the job I would find a way of clipping the cables up, sometimes you just have to bury yourself in the insualtion and get the job done. After you have been in the loft on a warm summers day though when you come down the ladder its like walking into an airconditioned room for a couple of minutes.

 

[u0362565]

90% of houses will have had insulation fitted after the wiring was done in the loft, then more insulation on top of it over the years. I know about derating factors etc but in all my time working in the domestic sector I've never come across an overheating lighitng cable in a loft, and that was when it was all fillament lamps, personally with most lighting LED now I see it as a none issue. I did once see a piece of 1mm cable that had slight signs of overheating but still seemed to work ok but that was when it was looped to two single ovens in a kitchen.

Personally I shy away from occupied rewires nowadays and the rediculous amount of loft insulation I have to contend with is one of the main reasons why. Sometimes if its been put down neatly you can roll it up out of the way and do the wiring but I would never leave the cables loose in a loft and if I was doing the job I would find a way of clipping the cables up, sometimes you just have to bury yourself in the insualtion and get the job done. After you have been in the loft on a warm summers day though when you come down the ladder its like walking into an airconditioned room for a couple of minutes.

Yeah I can see why you wouldn't want to do it. No one wants to take responsibility for lifting it because it's not a nice job in not a nice environment as you described. I came across a YouTube video where a guy had used metal cable trays in a loft, thought it was potentially a good idea, don't want to say electricians dream but probably easy to work on in future and it's visible, doesnt look great from a home owners point of view.

View: https://youtu.be/nCA8CrOzF10?feature=shared

 

[u0362565]

Yeah I can see why you wouldn't want to do it. No one wants to take responsibility for lifting it because it's not a nice job in not a nice environment as you described. I came across a YouTube video where a guy had used metal cable trays in a loft, thought it was potentially a good idea, don't want to say electricians dream but probably easy to work on in future and it's visible, doesnt look great from a home owners point of view.

View: https://youtu.be/nCA8CrOzF10?feature=shared

Doesn't get around someone having to lift insulation so old cables can be pulled out though. Unless they're left behind.

 

[oscar21]

To be fair, when I re-did all my own wiring on a fairly modern house when I first moved in I took all the insulation out of the loft and stored it in my kitchen for about a month whilst I did the various things I wanted to do in the loft. Cant see a customer wanting all their insualtion stored in the kitchen for a bit though.

 

[u0362565]

I'm leaning towards this, but not storing in the kitchen, must be a big kitchen! Did you just bin bag it up? Hmm when's that cold weather coming back..

 

[oscar21]

I'd ripped the kitchen out at the time so had space to store it. I just rolled it back up the best i could and carried it downstairs, but it was clean and not full of dust and soot like a lot of lofts I go in.