This question of adequate insulation bordering common areas is seldom asked.
Its becoming increasingly relevant, particularly in apartment buildings where -
- occupancy is less than full
- perimeter access points are not properly sealing.
- the management is saving on energy by not heating the common areas
I've inspected two apartments where lack of insulation created problems for the occupants.
- one where an uninsulated internal duct was causing damp and mould growth on the bathroom wall.
- one where lack of insulation on the ceiling of the car park was causing condensation in a bedroom above.
The calculations for heat loss used to discount internal shared walls or wall abutting common areas.
This assumed a generally good level of sealing of the common areas and occupied premises adjoining.
I don't advise spraying foam or beads into into cavities because it can be a hit and miss affair.
If your apartment is dry line there may be a space behind the plasterboard, but this is usually only 12-20 mm.
In order to get full coverage in such a small cavity (if that's even possible, which I doubt) the wall may be peppered with holes.
You may be better advised to inquire what kind of dry lining was used - for example whether it was sound-proofed and reline with insulated board.
ONQ.
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All advice on AAM is remote from the situation and cannot be relied upon as a defence or support - in and of itself - should legal action be taken.
Competent legal and building professionals should be asked to advise in Real Life with rights to inspect and issue reports on the matters at hand.