Re-wiring – anything I should consider?

Hello all. My first post here. My family and I live in a 3 bed split-level 1970s bungalow in Calderdale. We want to do a phased retrofit, but first we need to re-wire to replace the original wiring. A condition check showed it’s in a poor state.

It goes without saying we’ll be using low energy bulbs. We already have an electric hob and oven.

What else should we think about? Rewiring is a substantial amount of money and disruption so I’m keen to plan ahead.

We have gas-fuelled warm air unit for heating and hot water. Longer term we want a heat pump, so I’ll be sure to confirm the new consumer unit can handle the current drawn by one.

The resistance of wiring looses you power at the other end. Resistance (Ohms) is proportional to cable length and inversely proportional to diameter. You will therefore loose less energy (mostly as unwanted heat) by keeping wiring runs short and using more than the legally permitted minimum diameter allowed for a circuit. Electricians will always use the thinnest wire they can get away with and they fear that quoting for quality will loose them the tender, so you need to specify up front that you want the higher spec.
Also, get the electrician to use 100amp rated tails to the consumer unit, so that you are ready to upgrade your mains fuse to 100 amps. Your DNO should do the fuse upgrade for free.


I’d agree with Tim’s comments on power losses. I’ve just done my daughter’s house, depending on how confident you are its OK to put in the wiring and outlets yourself as long as you get an electrician to properly test the work and make the connections to the consumer unit.
Its also worth thinking about future proofing so a spare breaker on the consumer unit for a heat pump and or battery if you plan to have PV fitted, and if you have off-road parking putting in the wiring for an EV charger.

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If you’re looking towards a heat pump in future, would that:

  1. An air-to-air split system, with emmitters in each room (or maybe reuse the air ducting I’d you can find a unit that supports that)
  2. An air-to-water system
  • In which case, plan for underfloor heating seeing as you don’t have radiators currently
  1. A ground source system (which will probably be water heating too)

Either way, think now about where you’ll want the outdoor unit positioned, where it’s refrigerant or water pipes can run, and where in the building you’ll want to route them.

As yours is a bungalow it’s a lot easier as I imagine it can all route under the ground floors, except for the lighting which can just case up the walls via a switch easily enough.

My own plans are to have an accessible services running up the back of our staircase to run our wiring, water pipes and networking up. It’ll have shelves built Infront of it, but in a way that if we needed to add or change anything we could just empty them, take them out and get access to behind to fit/swap etc. It’ll probably just be a OSB pannel and some PIR to insulate the hot pipes from the cold pipes and saprate them all from the wiring.

Good point. I have 2 service ducts, water & electricity. One passes the rising main, the other the CU. If necessary plumber and electrician can work simultaneously without interfering with each other’s work.

@TomP, Rereading this thread, 2 things come to mind.

If your phased retrofit is planned to have IWI then ensure that all sockets and switches are on internal walls. Where this is impossible have enough slack cable to enable the outlet to be remounted out from the current wall surface, then it will be a simple job to just pull out some of the slack, rather than have to connect short extensions to the cables.

In case of impending old age (inevitable) or infirmity, fit sockets where they can be reached easily without too much bending/from a wheelchair. I did that in my extension when it was built and it was a godsend for my wife while she was ill. You may think it looks odd at first but you will soon get used to it.

You will have to get an electrician to do all the job, the idea of just checking at the end of the job is risky, at the minimum an electrician who was passing a job would want to see the plans and design, then do a first fix inspection to check cable routes etc, and then the 2nd fix, probably fitting the CU. I used to do that service for 2 builders I had built up faith in but not for most customers. You are asking him the use his name and registration to sign off work he may not have seen. The electrician will also be much faster than you.
The 32mm meter tails should always be fitted, but it may be difficult to get the main fuse uprated.
Think about Ethernet cabling from router to main PC and smart TV, the number of bad connections you see on the news etc is due to wifi. A new telephone cable slave as well.
There should always be some spare slots left on the consumer unit.
Are you planning for an electric shower which would want a 10mm2 cable.
Try not to have downlights as they are inefficient even with LED, and the plasterboard hole is often in a roof ceiling that gives bad heat loss.
If a bungalow then a service duct up to loft space would be useful. Is the floor a suspended timber or solid as that will set whether the wiring is dropped all the way down the way down a wall for a socket. Have a light in the loft, easily switched. Have enough sockets in rooms, as you’ll probably cover half of them with furniture.
Socket and light switch positions are already specified for easy access, sockets 450mm up and light switchs 1.2 m up from floor. It has been that spec for about 20 years.
Remember an outside 13A socket, and another exterior socket is you like Christmas lights.

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Thanks everyone.

I’m surprised at your suggestion @Tim_Gilbert about losses in the wires. It makes sense to keep lengths as short as possible purely to avoid wasting materials. I’m going to calculate the reduction in losses from using larger diameter wiring.

I’ll also make sure there’s capacity on the consumer unit for a HP and battery. We don’t own a car but are going to make sure it’s ready for an EV charger too.

We’re likely to get external wall insulation - plenty of space outside of the house and it’s cavity walls. So no need to worry about moving backboxes forward.

I agree with @Philip_Dustin - this is something that is absolutely out of my skillset. I can fit a new switch or plug but no way am I messing around with consumer units etc. And, yep, I have already spec’d double ethernet sockets in every room except the bathroom!

I will ask the electrician about 100A wiring between the CU and fuse.

We have a mix of suspended and solid floors. We also have full height ceilings with beams on show and Stramit board between them, so wiring in the ceiling is a non-starter. The sparky knows it’s going to be a tricky one!


 Larger size cable is a complete section in the regs, basically it 

comes down to keeping cable cool. It is very easy to end up with larger
size cable for a job, but you will then find that the accessories (
switches and sockets) are not designed to take the larger size. A
particiluar point is spurs on ring mains where most sockets will not
take 3 off 4 mm cables.


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Get your sockets and light switches air sealed, and try and stay away from downlights
Your hot moist air will find its way into the ceiling or loft and contaminate your insulation.
Air sealed house is the way to go but you still need good ventilation, HRV is the best for a sealed house

Yes, we’re getting a retrofit consultant in to do a phased retrofit plan and he’s told me how to tape the back boxes of the sockets. I expect the electricians will be surprised when I tell them!

My partner and I don’t like down lights - which is good really because full height ceilings combined with the pitched metal roof make them a pain to install anyway.

You don’t have to just tell the electricians. You need to supervise and inspect their work, at least until you see that they understand what needs to be done. Tracking down and rectifying air leakage after the event is a really difficult job.

Yep, that’s what I’m planning on doing. I’m going to take the week off work and as they chase out the (external) walls for each backbox I’ll prime then tape. I don’t trust them to do it properly.

We’ve got a blower test booked in. I’m intrigued to see what the result will be because the house isn’t draught. If we sleep with the bedroom door shut the humidity climbs to 80% within a couple of hours.

If this is your first blower door test be ready for a few surprises. I had one done a couple of years back, at dawn, midwinter, with simultaneous thermal imaging. What an enlightenment!

Do you reckon it’s worth doing thermal imaging in at the same time? I could borrow the Carbon Coop camera. Blower is booked for 12th Oct, so it might be a cold day.

Definitely book the camera and have the heating on. Take outside images during the high pressure stage of blowing and indoor ones during the low pressure stage. Leaks will show up hot on the outside and cold on the inside. If you are lucky the hot and cold areas will line up, so there is a straight through leak but it often happens that they don’t, as the leaking air is passing along cavities in the structure of the building, and I don’t necessarily mean the obvious one of the cavity wall. These are much harder to pin down.

Unfortunately if it is a blowy day the thermal images outside may not be clear and if it is a very blowy day the whole test may have to be postponed.

I’m in the middle of a DIY retrofit of a 1970s detached 2-story house.

A few things that might help:

We ripped out the suspended ground floors and replaced with solid. I had the downstairs rewired with all sockets wired down from the floor void above.

We already had downlighters upstairs and I installed a few more. We used this product in the loft: Loftleg Loft Lid Downlight Protector Hood |

We coordinated insulating the loft with rewiring the lighting. I removed all the mineral wool loft insulation and cut kingspan boards to fit between the ceiling joists. We cut holes in the kingspan for the down lighter hoods. I connected 60cm long lengths of flexible wiring conduit to the hoods for the lighting wiring: Polypropylene Flexible Conduit 25mm x 50m Coil Black | Toolstation

We foamed in the hoods and sealed the end of the conduit with silicone where the wiring came out into the loft. Finally we relaid the old mineral wool on top of the kingspan.

Where the lightswitch wiring came into the loft I added a length of flexible conduit to allow the wire to pass through the insualtion. Again I sealed the end with silicone where the wire comes out.

Suspect that you will find that your electrician will tell you that he’s not authorised to upgrade the meter tails - that the responsibility of your electricity supplier.

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