Discuss Backboxes in plasterboard on top of OSB in the UK Electrical Forum area at ElectriciansForums.net

Don’t usually get osb on the inside on loft conversions, depends on the architect really, but when I’ve come up against it I cut through both materials and then use a multi tool to remove a section of osb where the back box wings meet the plasterboard....think that makes sense?.....works for me anyways ?

ps I’d be concerned about the builder as well using that ---- insulation!
I did consider doing that - but was told the plasterer was in on Monday so didn't have a lot of time. Of course typical there has been no sign of the plasterer this week....
 
We multitool the box hole in the OSB slightly larger/longer than required, before the plasterboard goes on. Then once plasterboard its easier to find the 'hole' and cut out for the back box. Just use fast fix boxes.

One builder we work for uses it for noise suppression and says it makes it easy screwing anything to the wall as no plasterboard fixings are required (this includes his 2 bathroom wall lights which were £500 each)!
Sounds like the best option when you are prepared in advance...

Though any length of screw and you have sharp pointy bits through right where the cable is dangling in the cavity....
 
I think the use of ply or osb behind plasterboard, is to help comply with acoustics regs and fixing bathroom furniture, specifically with bathrooms or en suites. They normally put in some insulation in there as well. Its aimed at stopping you hearing people going for a tiddle. Not sure if that's the case in your new build.
In my case the use of ply on the stud wall was a structural requirement. Basically had to rebuild the house apart from the walls. ?
 
Good shout. The lower quality plasterboard boxes, eg the blue tab ones from toolstation, are good for this too as they can be fitted to thicker boards than the better quality appleby ones.

You say lower quality - personally I'm never going back to Appleby since discovering the blue winged ones (manufactured by CED).

The wings are on more of a 'ratchet' style, and you can lock them quite firmly in place to the plasterboard. A misplaced m3.5 won't push the wing back. Plus they go very far back - 20mm or more on a 35mm box. The spring loaded ones only seem to go back about 6mm. The spring winged ones have, occasionally in scenario is such as this one, caused issue by being a bit 'unsteady' or not going back far enough as in this case.

And on top of that they're cheaper! Used recently in a very similar situation.
 
For new builds here it's predominantly timber kit houses with service voids on outer walls. Internal walls can often be found with one side sheeted in OSB along load-bearing walls. What you've run into is common for us to find now. If we haven't been able to cut a section out ahead of the walls being plasterboarded, we will carefully cut through both layers with a multitool then fit metal boxes or appleby fastfix's with the wings cut off and wood screws in either side.

Personally wouldn't chose to use any other brand of fastfix other than Appleby having had more issues in the past with any other brand we've tried. Might pick up a couple of CED and give them a try though.
 

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