While I was replacing my kitchen ceiling I noticed that the floorboards from the upstairs flat (purpose built maisonette 1930) look rotten and water damaged. The flat owners are refusing to investigate as they said they "are dry" but I'm concerned the rot might spread and the structure of the floor is compromised. Basically I don't want it to fall in and harm my family members. Does this floor look concerning or normal? There have been repeated leaks from upstairs as it's their bathroom directly above this. Any and all advice and tips welcome.