Normally by fitting plasterboard. Direct rendering is not something that I've done and I've not come across a product.

Options could be just to fix the box in a hollow in the board using an extra long screw (or three). Lengths of plastic pipe, cut to length & filled with foam could also be used as stand-offs, in conjunction with a long screw.

Better would be to 3D-print some custom plastic stand-off brackets. Or adapters to interface between the Kaiser stand-off and the UK back-box (presumably the EU back-box can be unclipped from the product you linked to).

It may also be possible - but probably more expensive - to switch to an electrical range that is compatible with the Kaiser box. Jung, for example, produce a range of British Standard power outlets that I'm pretty sure are compatible with standard European back boxes. No doubt there are others who do so too.

Good call on the Jung range, I'll check that out

But, as you say, it would be an expensive option - IWI is expensive enough as it is! With retrofit of IWI becoming more important to meet UK energy targets I'm surprised there isn't a UK version of this.

Or maybe I'm not, we always lag so far behind the continent...

"OP, assuming you are a merchant, could you arrange direct import of said boxes?"

We manufacture and sell woodfibre insulation to distribution hubs, we are not merchants. To be honest, it's hard enough to UKCA our own product range, let alone a third-party product. Importing anything into the UK since Brexit is expensive and time-consuming enough to make bringing in accessories not worthwhile.

As I said to the architect, we can only specify the insulation. Would you expect Kingspan etc to sell electrical sockets? I can suggest various 'bodges', (alternative technical solutions ) but they add time and labour costs and require the electricians to agree to - and stick to - the method.

We all know that a lot of trades just want to bash it out, take the cheese and move on to the next customer.

Interstitial condensation is a real issue - we have both WUFI modelling and real-life experience to prove it. On the plus side, natural insulations will 'deal' with excess moisture better than plastic ones but we need a solution to stop it in the first place.

My solution to a similar problem was to have no sockets or switches on outside walls, as Nick mentions. But that is quite difficult and I can understand why it is uncommon. Upstairs isn't too bad since we could fit floor-mounted sockets in a couple of corners, but downstairs we have an extension lead all along one wall in a bedroom (I suppose I could have fitted the cable in the skirting board?) , a complete false stud wall in the utility room to allow sockets, plumbing and cupboards on an external wall, and a large extra box lime-plastered into the corner of the living room containing a load of sockets for TV & hi-fi etc.

But that was all because of my obsession with airtightness and wanting no penetrations at all in the inner plaster on the outside walls. In theory I believe I could have fitted Instaabox or similar but I don't understand how the sockets are mechanically secured. In general on the outside I dug a hole in the render and straw, filled it with resin and pushed a rawlplug or similar into the resin and then screwed into that once the resin had gone off. That seems to have worked with no failures yet.

I knew there'd be a reason I didn't do it

Could you use plastic backboxes designed for plasterboard? The lug clamp things won't work so you'd need to fix through the rear, through the insulation and into the solid wall with your insulated fixings.

You'll lose the depth of the backbox in insulation but you could offset that by removing a little extra depth of woodfibre and replacing with aerogel.

<blockquote><cite>Posted By: geuben</cite>Could you use plastic backboxes designed for plasterboard? The lug clamp things won't work so you'd need to fix through the rear, through the insulation and into the solid wall with your insulated fixings.

You'll lose the depth of the backbox in insulation but you could offset that by removing a little extra depth of woodfibre and replacing with aerogel.</blockquote>

I spoke to a builder friend yesterday, who is deeply involved with retrofit to PAS 2035.

He uses the Compac Foam or Bosig phonotherm 200.

For thinner IWI he chases this back into the wall for the back boxes to mount on – they will screw into the insulation without issue.

Where the cables enter the box, he seals the gaps with intumescent putty for airtightness and the same between the back boxes and the insulation.

So there are solutions, but fiddly and time-consuming compared to properly designed systems from the EU.

Having worked on plenty of building sites over the years I know that for your average workman fiddly means 'bodge it and get off site before anyone notices...'