If a house had mildew (I'm assuming it's mildew, it's black and slowly spreading) on the ceiling of the top floor of my house, what could cause this and how serious could it potentially be?
The building is a 3 story (minus the roof space) house in the UK. It was built in 1997, and the same family lives there today that moved in 16 years ago. If you want pictures or have questions, leave a comment and I will update the question. I don't know a lot about DIY/home improvement which is why I am asking here.