I've recently found a lot of damp around the bottom of a chimney breast at one end of the house. The house was built in the 1930s and at some time (I guess 20-25 years ago) a wood-burner and flue liner were fitted to this fireplace. There doesn't appear to be any ventilation into the chimney so I'm wondering whether that's the root cause. Having mentioned "root", I've hacked-down a damn great shrub that's been growing against the chimney since at least the 1970s and it's possible that has done some damage "down below". The room has a suspended floor, with an original decorative parquetry floor laid on the boards. The parquetry panels are T&G'd so it's not feasible to lift it to see what's happening underneath (I've got an inspection endoscope on order so I can look round the edges at the sides of some of the joists).
I haven't had to deal with damp before so would welcome input from anyone with knowledge.