Liability in case of moisture problems: What to do?

Questioner

In the past, an extension (kitchen) was built against the single-brick outer wall of our rear house by the neighbours. This extension of the neighbours does not have its own wall. Now, for a long time, there has been a moisture problem in this wall on the side of the neighbours. It is still unclear where the moisture comes from, possibly from the higher part of the wall that is still just an outer wall. Are we, as the owner of this wall, (partly) liable for the moisture problem of the neighbours?

Lawyer

No, the perpetrator, however this is now a shared wall for which the costs of normal maintenance and replacement must be borne jointly.