Moving sockets for internal insulation

22 Jan 2012
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United Kingdom
A cold part of our house is soon going to be internally insulated using Kingspan boards with bonded plasterboard. The total depth should be 52mm

This will mean moving all the sockets.

- Should I use metal 35mm boxes, mounted on 15mm of ply, or PVC boxes? I've seen suggestions to use the PVC boxes, but not sure how that would work, trying to hollow out insulation for the lugs?

- Should the cables to the sockets be clipped to the existing masonry wall, and the insulation cut back to allow for them, or is there a better way?

Thanks for all assistance.
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47/48mm deep metal boxes are also available.

For a plastic dry-line box, the insulation can be hollowed out easily enough to accomodate the lugs.

For a dry-line box, this should be cut in after the board has been fitted to the wall, not before. The box can be cut in with a padsaw, and no need to cut the insulation back to the original wall - leave a thin bit of insulation to avoid a cold spot as best you can.

Metal boxes or dry-line boxes are fine, whichever you prefer.
Not sure why the cables are an issue, I assumed you were moving the sockets forward only.

Presumably you are adding some more.

I can't see why a small notch in the board insulation would be a problem. I would be inclined to protect the cables with some capping.

The other alternative may be to chase the cables into the existing wall, if that is possible.

There may be issues with cables getting hot from the insulation.
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There may be issues with cables getting hot from the insulation.
There may.

There may also be issues with mould growing all over the cold walls because the vapour barrier was breached in order to fit recessed sockets and wiring.

pahtboy - when you apply for Building Regulations approval don't be surprised if they want to know how you intend to comply with Parts C and P, as well as Part L.
The main thing you need to do is make sure there's insulation behind the back boxes otherwise there will be condensation and the boxes will rust and other associated problems.
Beyond that I'm not sure exactly how to attack them, maybe to the plaster board would be best.
Hi all,

To answer various queries:-

- I thought it better to move the existing sockets forward so that the insulation board can go behind them, or a piece of wood which will have a small insulating value (better than the current situation) in metal boxes were to be ised, instead of just extending the boxes forward and allowing a cold path through. Sounds like pvc plasterboard boxes may be the best bet though.

- The thought on moving the cables was so they don't come in via the back of the socket box, making a cable hard to replace should it become necessary in the future. If they were clipped to the wall in a slip tube they may be easier to change should the need ever arise, and would be in contact with the block wall so not surrounded by insulation. But I suppose it would save some effort to leave them as-is, and I know there is a decent amount of slack cable in the crawl space.

- No additional sockets are to be added (I may even remove one), they are just to be moved forward.

- The builder who has so far quoted for doing work (Not including moving the sockets) has said he will install a VCL to the wall in addition to the one provided on both sides of the Kingspan boards.

The room is not extremely cold, it is a cavity built extension. The rest of the house is solid blockwork, which has been externally insulated last year. Only since that work was done has this room felt cold, as previously it would have been the warmest room.
Why can't you just use longer machine screws for the sockets?
Not all cavities are suitable for filling.
Have you thought about balancing your heating system a bit? Maybe it's just cold because the heating in the rest of the house is tripping out earlier. You could try moving the thermostat to the colder room, or even add a zone for the old and the new separately.
Might be a lot cheaper and less disruption, especially if you're only worried about the coldness relative to the other rooms.
I don't want to fill the cavities, having read far too many horror stories about it, with areas not getting fully filled, slumping, and damp coming through. Internal insulating seems like a better option.

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