Thanks AJ, it's really kind of you that you show such interest.
We have been living in the property few years so we knew that both flats were poorly insulated. When the bottom flat was sold and a new owners started thorough renovation we asked them to consider to remove their old ceiling (which was in poor condition) in order to put soundproof material over it. We told them that it would benefit both flats so we will pay 50% of costs of this operation.
It was only a general proposition without any details. After a few months of renovation the new owners called us to their flat and told us that they could not remove the oryginal ceiling (in order to place sound proof material over it) because the ceiling turned out to be asbestos. But because they recognised the need of sound proofing of our flats they just build a soud proof barrier under the oryginal, asbestos ceiling - in form of suspended ceiling - not over it like we proposed.
They presented as with a high bill and asked to pay "like we promised". We were suprised because any details of work were not discused with us and it costed more than we expected. But they argued that they will move to the flat very soon, we will be neighbours, we cannot start our relationship with a conflict, that we should be decent people, that asbestos in their flat was fitted benefit as a fire proof barrier etc - so we finally paid the bill.
Now, when the renovation is finished, no-one is living in the bottom flat - it is again.
Our building is Victorian villa with originally high ceilings and other historic features. We are afraid that another new owner who will buy the bottom flat can say "I do not like my lower ceilings. I want them high again" and that they dismantle what we paid for.
When the current owners instoled halogen lamps they did not damaged our flat at all. They just demonstrated that they do not treat the new build structure as a sound proof barier but just as their ceiling ( I paid 50%).
We would like to do something to ensure that the next owners of the bottom flat will know that what they have over their heads it is not just "their ceiling" but a sound proof barrier we paid 50% of costs. Is it possible?
PS. sorry English, it's not my first langusge