Back Boxes for 57.5mm Dab n Dot Insulated Plaster Board

[MJPD29]

47mm metal boxes and long screws

 

[westward10]

If you have an electrician signing this off he is the best person to ask as he can see the installation and give correct advice. If you feel you are pestering him then compensate him for his time.

 

[Silly Sausage]

Due to regs, and the house being a 1908 solid wall construction, I need to include 57.5mm Kingspan to all external walls.

What are your Building Inspector's thoughts on you putting 20 odd holes in the wall insulation? Surely that's going to create cold spots and compromise the specified U value (whatever it is) of the walls.

 

[Grant webber]

Cut plaster board boxes in after the plasterboardings done. Put the bit of insulation u cut out behind the back box so there's no holes in insulation. Bring cables into box. Job done.

 

[telectrix]

do it right. 35mm back boxes onto brick then 25mm skeleton boxes to make up the space. that way the cables are all enclosed.

 

[HappyHippyDad]

When I had this situation the builder kindly cut an area of the insulation off of the plasterboard where the back box was going to be. He cut quite a large area so that the wings of the plasterboard box easily pushed out. He didn't cut into the plasterboard.

I keep 2 types of plasterboard boxes on the van. The appleby ones as they seem sturdy and a different variety for when the plasterboard is too thick for the appleby (which happens quite a lot). I've never had any problems using them and can't see why anyone would.

Seeing as though you are the builder you can be kind to yourself and cut away some of the insulation before you put the boards up so that you aren't using all sorts of strange implements to chip away at the insulation through the box hole.

 

[123]

Tend to find on this kind of job that the socket back boxes are where all the condensation etc ends up. I'd give the dry lining boxes, with some form of insulation stuck behind them the most thought.

Metal back boxes over time will rot, and if you cut a huge wack of insulation out for plaster board boxes, it kinda defeats the purpose of installing it to begin with.

 

[stevethesparks]

Extension boxes if necessary

 

[Deleted member 26818]

If you know where you intend to site the sockets and accessories, you can fix the wiring in place before dotting and dabbing the plasterboard, then cut out the holes for the back boxes and just pull the cables through into the back of the boxes.
Plastic dry lining back boxes would be ideal and any lip would be hidden by the skim of plaster.

 

[Jamie Harper]

If you know where you intend to site the sockets and accessories, you can fix the wiring in place before dotting and dabbing the plasterboard, then cut out the holes for the back boxes and just pull the cables through into the back of the boxes.
Plastic dry lining back boxes would be ideal and any lip would be hidden by the skim of plaster.

All great answers at last! Thanks very much!

A mix bag but its good to know my options and different methods. I agree that cutting a big hole out seems a waste but it may be the best option, strange only 1 person mentioned the skeleton boxes, i thought this would have been the "correct" way to do it?
As also advised i will have a chat with the electrician who will be signing it off.

 

[Andy78]

When I had this situation the builder kindly cut an area of the insulation off of the plasterboard where the back box was going to be. He cut quite a large area so that the wings of the plasterboard box easily pushed out. He didn't cut into the plasterboard.

I keep 2 types of plasterboard boxes on the van. The appleby ones as they seem sturdy and a different variety for when the plasterboard is too thick for the appleby (which happens quite a lot). I've never had any problems using them and can't see why anyone would.

Seeing as though you are the builder you can be kind to yourself and cut away some of the insulation before you put the boards up so that you aren't using all sorts of strange implements to chip away at the insulation through the box hole.

The trick with Appleby boxes is to trim back the white rails at the side of the box with a knife. This lets the yellow tab sit further back in its final position.

 

[HappyHippyDad]

The trick with Appleby boxes is to trim back the white rails at the side of the box with a knife. This lets the yellow tab sit further back in its final position.

Cheers Andy, I've got about 100 of them in the shed so I'll have a little practise with that.

 

[stevethesparks]

All great answers at last! Thanks very much!

A mix bag but its good to know my options and different methods. I agree that cutting a big hole out seems a waste but it may be the best option, strange only 1 person mentioned the skeleton boxes, i thought this would have been the "correct" way to do it?
As also advised i will have a chat with the electrician who will be signing it off.

It is the correct way to do it, they are also called extension boxes.

 

[Bellendian]

Just looking at it from an electrical perspective, 35mm galv boxes spaced off the wall with offcuts of copper tube cut to length would give a decent fixing, combined with a good bead of adhesive around boxes as you're boarding the wall.
From an insulation side though, this does compromise the vapour barrier and may lead to condensation.
Last solid wall internally insulated refurb I worked on, used a different detail.
Walls were lined with celotex, and this was fixed using 2x1 batten secured to wall at 600centres on warm side celotex.
Services run in this batten cavity, p/b screwed to battens, dryliners fitted to p/b for accessories.
Total build up was 60+25+12.5mm though...took up at lot of space.

 

[Michael Monaghan]

Screw the 35mm deep metal box to the brick slab the wall then on second fix cut the box hole neatly and use an extension box . They come in 25 or 35 mm deep so with 2 x 35 mm boxes you'll be about just right
I'll try upload a photo

 

[dksanders]

I have an local electrician who has agreed to sign off. He will monitor the work throughout. Just wanted to get everything right first time, know as much as possible and make sure the installation goes smoothly.

Is he Third Party Certification registered?

 

[Loky11]

Make sure you mechanically fix the p/board if you dabbing insulated boards, they can pop off during fires and block fire escapes.

 

[Michaelwgroves]

I don’t like the idea of dot n’ dab on a solid external wall. I’ve had this dilema on a number of projects. I prefer to use a stud system. Take a look at Tradeline from Travis Perkins, it’s same system as British Gypsum but much cheaper.
http://www.tradelinedrywall.com/products/metal-solutions/wall-liner/
It only adds 18mm to your solution, less thickness of dot n’ dab, so maybe total extra 10 mm. But you can also plumb wall and run wires and pipes in the 18mm void. No risk of damp pushing it off.
You can put OSB in void for fixings, so no problem if installing kitchen units etc.
Then just install 25mm dry line back boxes and no need to cut insulation. But if you need deeper boxes, Celotex 60mm is 3 * 20mm so just scrap off top layer.
In reality the loss of 10mm is unnoticeable, but a stud system gives you so many benefits.

 

[EalingBadger]

A bit late with this comment and the problem has already been alluded to by a couple of other posts, but if you do not have any insulation behind those metal back boxes then you will get condensation and you will get the boxes rusting out over time. The only way to avoid this would be to hermetically seal the sockets - something that is simply not practical, and that's without even considering the fact that every single socket has three great big holes where the plug pins go on the front of them.

 

[Michaelwgroves]

A bit late with this comment and the problem has already been alluded to by a couple of other posts, but if you do not have any insulation behind those metal back boxes then you will get condensation and you will get the boxes rusting out over time. The only way to avoid this would be to hermetically seal the sockets - something that is simply not practical, and that's without even considering the fact that every single socket has three great big holes where the plug pins go on the front of them.

I'm not sure if the mention of metal back boxes was in relation to my post or another, but to be clear, dry line back boxes are plastic. Furthermore they sit in front of the insulation.