Can the outdoor unit of our neighbour's air conditioning unit be hung on our outside wall?

Questioner

We live in a terraced house. Our living room protrudes from the rear facade of our neighbours. On the outside of our living room wall (which is on the property line) the neighbours have hung an outdoor unit of an air conditioner. When the air conditioner is on, disturbing low-frequency vibrations (humming sound) penetrate our living room. At first I thought that the wall was shared, but I recently read that due to horizontal extension the wall is in principle not shared, but our private property and that therefore the outdoor unit would actually also be our property. This results in a strange situation, on top of the fact that the air conditioner is causing us nuisance. Is it wise to ask the neighbours to hang the air conditioning on their own back door or to place it on the ground?

Lawyer

If the wall is exactly on the property line, then the neighbours are each the owner for half the thickness of the wall. Then the neighbour is allowed to attach things to his side of the wall. If this wall were not shared but fully your property, as you say, then the neighbour is of course not allowed to attach anything to it. However, regardless of whether the neighbour is allowed to attach something to the wall, neighbours are not allowed to cause each other a nuisance and if the presence of the air conditioning on this wall causes you a nuisance, then you can in any case already on that ground request the neighbours to move the outdoor unit or change the attachment structure.