We live in a rented house we've been in since January - pretty standard 1930s semi with some nasty, slightly weary plastic double glazing.
There were a couple of patches of what I thought were damp on outside walls when we moved in, but they were in the spare room so I didn't do anything about it.
I cleaned some blackish mould-looking stuff off the window frames a few months back, in almost every room. I'm now noticing that it's returned, plus on some walls and it's spread to the curtain linings.
I'm a bit of an open-window fan, so I'm finding it difficult to believe there's a ventilation problem. Having said that, we do have to dry non-tumble-dryable clothes on radiators in the winter, and the extractor fan in the bathroom broke a couple of weeks ago so that's probably not helping.
I usually avoid all cleaning products where at all possible, but is this a 'bleach or nothing' situation? Any other ideas on how to both clean it and stop it coming back? In addition to the black stuff we now have some green mould too, at the top of an upstairs bedroom wall too.