Upgrading loft insulation and wiring

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Doug71

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I am upgrading the insulation in my exes loft from 100mm to 270mm by laying some 170mm insulation perpendicular to the existing so it also goes over the joist.

We have had an electrician in as some of the ceiling lights are being replaced by spots, he has also tidied up the wiring in the loft a bit but there are still wires running all over the place.

There are some wires which run over the top of the 100mm insulation which will be covered by the 170mm insulation, is this acceptable or do they really need to go totally under/over the insulation and not through the middle? I'm pretty sure they are all lighting circuits, certainly no electric shower or cooker cables.

As always Google gives mixed answers 😂 I am going to run it past the electrician tomorrow ( he did know what the plan was) but thought I would run it past the knowledgeable ones on here first.

Any thoughts?

Thanks, Doug
 

SamG340

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Don't forget that a cables amp rating changes when you bury it in insulation, could be an issue if it's sockets
 

flying haggis

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are the replaced lights downlights or surface spots and are they led. if they are recessed downlights do they have fire hoods?
 

Doug71

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are the replaced lights downlights or surface spots and are they led. if they are recessed downlights do they have fire hoods?

They will be recessed down lights, just a hole in the ceiling with a wire hanging down at the moment though so not sure exactly what is happening with them but I was told it's okay to run the insulation above where they are going.
 

flying haggis

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Some newer led downlights can be covered by insulation but ideally you should have a sort of cover
to aid airflow and keep the area cooler
 

Scruples

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In the early days of metric cables 1.00mm² TWE was acceptable but as we rolled away from the 60s/70s it was realised that, with added insulation in the roofspace, the cabling for lighting was a bit small and may get too warm. All new lighting circuits now should be 1.5mm² TWE.

Having said that, if you are changing from incandescent lighting to LED lighting in the house then your current demand is going to be much, much less. For example: in my bathroom I had 2 ceiling fittings with 60W incandescent lamps (total 120W). Changing to LED 9W lamps and the total load was reduced to 18W. A massive drop in energy.
If you have enough slack on the cables in the loft then run them over the insulation. If not, then it's time to consider upgrading the upstair lighting cables if they are only 1.00mm². (The size of the cables are usually marked on the cable sheath.) The work isn't to onerous for a small to medium house.
 

morqthana

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What this shows is that the worst case (Method 103 - cables completely surrounded by insulation) gives even 1mm² an 8A capacity, so if all you've got up there are lighting circuits you'll be fine.

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As for covering up downlighters - yeah, see what the maker says. Firehoods are almost certainly optional, as tests have shown that downlighter holes don't affect the fire performance of a plasterboard ceiling enough to require them, if it's just a loft. Different story if it's flats.

But you might want sealed enclosures over any lights in the bathroom, as you really don't want steam getting up there and making the roof damp. You can buy them, but they're pretty much a PoP to make from plasterboard offcuts, those short bits of 20x20 you've kept in case they come in useful, and silicone sealant. Some people use clay flowerpots with the drainage hole blocked, but they're heavy, as you need a generous amount of space around the lights if you're sealing them in.
 

Spectric

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Considering the price of electricity then it would be worthwhile to ensure all lights are LED and then the cable is more than adequate so definately no problems. One issue not mentioned is the ambient temperature in a loft can become very hot, but again go for LED's and don't worry.
 

morqthana

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One issue not mentioned is the ambient temperature in a loft can become very hot,
True, but even at 50° the capacity is still 6A (5.7 for the precise). And don't forget that insulation reduces heat travelling in to the cables just like it reduces it getting out.
 

Sideways

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Changing the insulation potentially invalidates the original design and creates a fire hazard.
We can't teach you electrical design calcs here.
The smart move would be to get it checked for peace of mind. Mention installation method 103 and derating for 40C ambient.
It may well be fine and even if not, if you plan to use LED lights, replacing the breaker in the consumer unit with a lower rating device is cheaper than changing the wiring.
What matters here is that the circuit breaker in your fusebox will allow a certain level of overload current through for days without tripping. The wiring, subject to the installation method, ambient temp, bundling with other wires, etc must be able to carry that overload without getting hotter than the 70C temperature its insulation is rated to.

As above, the real concern isn't so much lights as any high power / long duration circuits that might run through your loft. Showers and immersion heater cables are candidates.
 
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Doug71

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Thanks for the advice chaps.

I spoke to the electrician and he was fine with the insulation going over the cables, because of the new spots he has replaced quite a bit of the wiring so guess he's happy that it's to regs.

Apparently he has put a lower amp fuse/breaker in somewhere because he wasn't happy with some of the other wiring or something.

The houses were built in the 70's, nice looking houses but some of the workmanship leaves a lot to be desired. They all have wall lights around the living rooms, the wiring for them just runs right round the room from one light to the next about 6' off the floor, just where you would put a nail in the wall to hang a picture on. Where there is a window in the way of said wire they just ran the wire downwards on an angle under the window board then back up on an angle to the next light 🙄
 

eribaMotters

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I had a similar situation when I did our refurb in 2018, but I replaced what was about 50mm of insulation with 400mm. Ideally wires should be either all above or all below, only so you can trace them/have no surprises.
All new wiring I used 1.5mm T&E, but left existing 1.0mm T&E. LED's draw about 1/8th of old style filament lights so the load on the wiring is fine.
The new LED downlighters also run nice and cool. I left a cereal bowl sized gap in insulation butting up to lights but ran 2nd layer. The electrician who signed off my work was happy with this meeting regs.

Colin
 

Spectric

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Dougs thought process was good, he wanted more insulation and actually realised there might be some impact on the wiring and then got an electrician to provide the right information and check things out so he can now have peace of mind. It is a shame that many people just blindly do things without even thinking there may be consequences at some point in the future, when you come across these horrendous bodges it can be amazing that the customer is really unaware of what they have done wrong, yet to yourself it just screams out as a total bodge. Domestic wiring has always been something where you come across such bad workmanship and it is not always the home owner at fault, Joe from down the pub is often the culprit and is why industrial is so much nicer to be involved in, they don't let Joe in!
 
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