Hi. I have a flat in a house, converted in the 80s. The owner before me lost some of the floorspace in the living room to a layer of sound insulation that he installed on the party wall that separates my flat from the flat next door. Must've been about 8 cm looking at the wall depth in other rooms.
A few years ago, next door neighbour renovated their kitchen and built into this sound insulated wall to make their kitchen bigger. We are now left with a thin plasterboard separating our flats and there is no room to build another layer of insulation due to the position of the door frame. So, in effect, next door have built into our flat.
Is there anyone with experience of this? Neighbour is denying this though it is quite clear that he extended his flat and we list the sound insulating properties of the wall. Help!