I really want to see a picture. I find it hard to believe the boxes are set 6" deep, but if they are, I want to see how it is done. I'm considering the possibility of e.g. a single-skin workshop with an extra leaf of blockwork added to make it into a habitable room.
I am not ignoring this thread, I will post a pic of the backing box tomorrow as I am using my phone to take the pics and it is too dark with the electricity off.
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