Rewiring and internal insulation

[Spillo]

The house we're buying will need rewiring and it is also very poor on energy efficiency (EPC E) so we need to insulate and it's looking like it needs to be internal wall insulation rather then external. How does the insulation work interact with the rewiring work? Would it be first rewiring and then insulation? Do they overlap at all e.g. some insulation needs to be done before rewiring can be finalised? Does anyone have any experience of having these two things done?

Also, if anyone has any experience of costs involved, that would also be hugely appreciated. In case relevant, the house is a four bedroom semi-detached in SE London. I'm totally at sea and wondering what to expect on several counts: practicalities, costs, etc. etc. We're absolutely not "project" people and I'm feeling pretty daunted and stressed out. So much so that it's making me wonder if we should go ahead with the purchase. :-(

When you say needs a rewire assuming that this has been based upon a professional inspection / electrician recommendation? I’ve recently had the floors and everything up in the downstairs of our home to replace the mains water, and whilst I was down there I did the insulation in the floor cavity (Victorian terrace). What difference this makes will have to wait until this winter when it’s usually colder indoors than it is out until the heating turned on. Also whilst I had the floors up I replaced all the wiring and plumbing too so that it is all new.

The reason I mention the above is that it will largely decide what sort of hassle your electrician has to go through. If you have a house with a cavity gap under the floor then it will most probably be simple for him to run the wiring under that / around the base of the walls with no need to disturb anything / very little. I’m guessing given your EPC rating it is an old house, therefore the above probably applies. This will also feed into the insulation question - do you know if you have single brick walls, cavity and so on? If a Victorian era home then you’re likely not going to have any joy trying to get insulation into the walls and so will be looking at adding it internally either through false walls or insulated plasterboard etc.

In terms of cost I don’t really know as I did the work myself. Materials wise to replace the ground floor of a 4 bed terrace with new wiring, a new water mains pipe, associated plumbing and copper pipes for that was maybe a few hundred quid, but of course it took about 5 weeks of my time which is where it is going to add up for you. I think for a total rewire of a house in London and making good the plaster you could be looking at between 6 - 10k depending on what needs tearing out. To insulate all the walls you are looking at money +++ I would say. I have just build a roughly 4m squared garden room and the insulation for that alone (PIR panels) cost about £800, so extrapolate that to an entire house with labour ontop and I think you can probably spend the same as the electrician again.

Just to add to the above I had to have a professional electrician in to wire up my garden room for regs sign off. A new two circuit consumer unit, six ceiling lights and four double sockets came to £780 (SE London, June 2023) with me supplying all the materials. When we had our consumer unit replaced about 18 months ago it was £2400 with a new 32 amp circuit fitted for the oven and the shielded armour cable run into the garden in preparation for the garden room.

We had 2 rooms in an old house that needed replastering anyway, each about 12' x 14'. We battened out the inner brick leaf of the 2 outer walls in each case and had insulated plasterboard fixed to that, then skimmed. The electrics went between the old brick inner layer and the insulated board, in the gap formed by the wooden battens (just under 1"). First fix electrics after battening but before boarding. Works fine provided you can accept that the whole shebang takes a few inches off the walls. And make sure that if you plan to hang anything on the walls, like radiators or kitchen cupboards, you put battens in where the brackets will go before it is boarded out.
Costs is a difficult one, one room was the kitchen, had to have a separate supply and lots of electrics, close to four figures for that IIRC. Other room, not done at the same time, had been rewired recently so didn't cost a lot just to tweak the wiring a bit put in new sockets (plastic ones in the insulated board rather than the previous ones chased into the wall) and was part of another job. Plastering, over 1K for the kitchen, but we had the internal walls skimmed as well and bits of that job were complex. Other room done as part of a bigger job, so costs difficult to disentangle.
Our plasterer is expensive for round here -NW England (but very good). A cheaper one quoted about 650 for the kitchen, IIRC.
It's a lot warmer than it was when it was just dot-and-dab thin plasterboard direct on the brick in one room, and chipboard on battens in the kitchen.

If your fixing battens with insulation board fitted between it's easiest to fix battens first then 1st fix electrics then sit insulation on top of the wiring.
That way the Sparks can run between battens and you avoid having to fix battens at a odd spacing which makes them harder to find in the future.

Thanks v much for the input - really helpful! We haven't yet had the survey or any inspection - we just know from having viewed the place that the electrics will need doing and we're assuming it's a full rewire. And the insulation work needed is clear from the EPC.

How long did the work on only the garden room take the electrician to do?

Forgive the daft question but did the fitted kitchen units need to be removed for the electrical work?

About taking a few inches off the walls (which we can ill afford), I'm looking into how "thin" the insulation material can be - I gather the thin stuff is really expensive.

Makes total sense - THANK YOU for the pointer.

Two fixes. First took about 6 hours and the second about 3.

The only way to know if the electrics need doing is to have them tested. When I ripped mine up there were plenty with the old black / red wiring from the early 80’s at best but likely long before. No faults or issues and they are some 45 years old. You could conversely have a brand new insulation that has been flooded with damaged wires that all needs ripping up. Many electrical wires go on for decades with no issue.

I have been assuming that the surveyor will test the wiring. We're paying (a fortune!) for a full structural survey. I'm really hoping that we don't need to get an electrical to do an inspection too.... but perhaps I'm wrong about that. This is all new to me.

That's pushing it tbh. Average lifespan of wiring is 30 to 40 years after which random faults will start to appear as the copper degrades

On that basis I can be sure the place needs rewiring because the vendors have been there 30 years and haven’t done it in that time. Thanks!

The life of electrical wire kept in good condition is in the region of 50-70 years. It’s all about installation, load and conditions. If exposed to damp etc then will be much much less but I have electrical wire upstairs from the 70’s and zero issues. Copper doesn’t degrade, it’s the sheathing around it.

Get an Electrical Condition Inspection Report done, costs about £200. Will give you a more accurate idea what needs doing

No they won’t test the installation. They will issue a report saying something along the lines of we couldn’t inspect the electrical installation secondary to <insert reason> and we would recommend you get your own independent inspection. The survey is only going to pick up something glaring which is of use of course if you have no idea what you’re looking at, but even the most expensive survey isn’t going to go ripping up carpets etc as you don’t own the property. We got the mid level survey and to be honest it didn’t really tell me anything I didn’t know already but I guess it might have picked up serious issues should there have been any?

No, please don’t listen to this advice, it’s wrong. I’ll repeat, the only way you are going to know if the house needs a rewire is from an electrical inspection report. Circa £1-150 depending on area of the country.

The above message in relation to this.

It does around points of resistance such as terminals

OK that's really helpful, I had not heard about this report. Would it be normal to get such a report done before exchange on the purchase? I mean does the person who does it need to do anything "invasive"/"damaging" to the property in order to carry out the assessment?

Understood, thank you.

I took AGES to find a surveyor I liked the sound of (after two useless surveys for previous purchases). What's the best way of finding someone reputable to do this electrical inspection? I guess you're going to say Google.

Checkatrade! Got it.

Yup checkatrade or similar a good place to start unless you can get recommendations. Electrical report won’t need to pull anything apart so no issues on that side. I’d ask you however is the result of that going to change anything? In other words, if it does need a rewire are you going to pull out of the sale? I would say you’re really unlikely to be able to negotiate any sort of discount should anything show up. Yes you’ll be forewarned about a potential expense but for us we didn’t bother with any inspections prior to exchange. Survey said all the usual jazz about get a professional report on this that and the other but we’d have wracked up however many hundreds doing that so decided against. Up to you I guess and what value it’s going to add?

Fair point.

30-40 years is not average and random faults dont just appear. The wiring in our garage i would estimate to be between 75-90 years old ( rubber cable and bakelite fittings ) and hasn’t had any faults in the last 5 years we’ve been here. I wouldn’t fancy touching it now but it just goes to show how long it can last.