In the middle of having some work done at home, and asked for the builders to insulate my suspended wooden floor. Somewhat suspicious when I came home to find they'd declared it "done" with only two floorboards lifted, I pulled one up and found this:

https://photos.app.goo.gl/jmfsyULSKzelFtke2

Basically what this guy's done is cut the board up into chunks and then randomly stuff them into the void under the floor in a big jumble. Massive air gaps everywhere, no vapour control layer, none of the insulation actually in contact with the floor. Mindboggling.

I think I can see where you went wrong. You didn't tell them HOW you wanted to have it completed. Should have shown them some specs!!

Maybe it was all packed in but a sudden gust of wind created by one of there other bodge jobs they'd completed. So WHAT else have they completed for you? If they can't get this right...

Posted By: SeretJust out of interest as I'm not a sparky, what is best practice for running a cable like that through a layer of insulation? I'm assuming a conduit, but what sort of diameter conduit should I be seeing and do the materials matter?

I'm not a sparky either, so double-check my answers.

If a cable runs through insulation, then it has to be 'de-rated' - it will run hotter because of the insulation so it can carry less current before it gets too hot. Running through insulation, as opposed to being embedded in insulation for a longer run, is not too bad. I think (but double-check!) a cable can go through up to 6" of insulation before it has to be derated.

There's a particular problem with polystyrene insulation because of the plasticisers in the make up of electrical cable. The plasticiser is 'sucked' out of the cable and into the polystyrene, even if they are just touching, and this leaves the cable insulation brittle. So it eventually falls off and the cable can cause a fire as a result. See e.g. https://www.esfrs.org/black-museum/all-the-black-museum-cases/pvc-cable-insulation-and-polystyrene-insulation/ But your insulation doesn't look like polystyrene so hopefully you're OK.

A conduit is a good idea to make it easier to change the cable later. Make sure you get a proper certificate for the electrical installation with insulation and earthing tests and don't hesitate to complain to their professional body if there's any problem.

Personally, after I'd seen that under-floor insulation, I'd be having a chat with the builder. I'd expect that he'd be off my site forthwith and not expecting any more money from me. Though he might have a good story, but it would have to be very good for him to be there for another minute.

Seret writes:

''TBH the guy who's doing the work is otherwise just doing internal fit-out work (eg: skirting boards, fitted kitchen), nothing technical. Not sure why my builder asked him to quote for this work, somebody else should have been got in.''

As long as you don't have to pay anyone anything, and they clear away all their mess then (apart from not having the floor insulated) you have not lost too much (apart from some faith in the person concerned, I guess).

I was once asked to look at a job which was even worse, but did not include the potential electrical catastrophe which you point out.

No better than no insulation at all.

Is that not normal BS work? Seen plenty along the same lines but that does take some beating.

Fitting a kitchen on a new build the other day and could not help but notice the gaps in the insulation around the edge of the floor. Sure they will plaster board up the holes so we wont be able to see the gaps in the future

Do it yourself, then you know that the attention to detail is at the level you want.

Posted By: sam_catDo it yourself, then you know that the attention to detail is at the level you want.

Well yes, guess what I just spent my Sunday doing?

At least it's sorted now. As a bonus when I got under there I found that whoever had installed the CH in years past had left the pipes uninsulated and lying on the ground. Wonder how much gas I've burned over the years to heat that dirt? So lazy.

Bendy plastic pipes Tony.