Depth of backboxes for dot and dab

[Moonshine]

My sparkie has installed back boxes cut into the block work, and they don't seem to protrude a lot out of the block.

 

These walls are going to be dot and dabbed and skimmed, which could be 20-30mm gap from the block to the front of the plasterboard.

 

In my head i thought that the backbox should protrude out the wall so the front of the back box sits a few mm behind the front face of the plasterboard, but it seems to be a fair bit behind that.

 

Anyone got any ideas of the right distance?

Edited December 1, 2022 by Moonshine

[TonyT]

You are correct, boxes should ideally be a few mill behind the plasterboard.

you can buy extension boxes that screw onto the original box to bring it out to the depth, these are a pain.

 

don’t let them use long 3.5mm screws and have a gap.

[Temp]

Personally I like deep back boxes. Let's you squeeze in home automation devices later.

 

Ask for a Neutral at all switches if you can.

[ProDave]

4 minutes ago, Temp said:

 

Ask for a Neutral at all switches if you can.

"Loop at switch" is the phrase your electrician should understand

[Radian]

2 hours ago, TonyT said:

don’t let them use long 3.5mm screws and have a gap.

 

Oh yeah, all ours have 50mm long screws to reach the back boxes.🙄

 

Apart from the near impossibility of finding the tapped holes at that sort of depth, the 50mm screws must have been the only long ones available as some bottom out at the back of the box. Either that or the sparks was a sadist. I didn't understand that this was happening until the threaded tabs started breaking off as I kept on tightening the screws.

[MJNewton]

3 hours ago, Moonshine said:

Anyone got any ideas of the right distance?

Deeper the better is my preference, within reason of course! Gives more room for smart relays, dimmer modules, easier/neater wiring etc. Also far better for them to be too deep than too shallow thus require retrospective remedying! 

[TonyT]

You could use 35mm boxes and screw straight into the wall and tell the dot dabbed to bring the board out to the level of the box.

 

 

[Moonshine]

7 minutes ago, TonyT said:

You could use 35mm boxes and screw straight into the wall and tell the dot dabbed to bring the board out to the level of the box.

 

We are already using 35mm boxes and they are recessed back into the block with holes cut. I have gone through it with sparkie and he came up with the simple solution to use 47mm back boxes rather than pack out the 35mm. Should work o.k, with the advance of having deeper space for sockets etc

Edited December 1, 2022 by Moonshine

[MJNewton]

One day you'll be thanking him... 😁