My wife's sister lives in a detached 1968 house in Hasting, Sussex. Its built on the side of a hill. The hill is pretty steep so the back of the house is
3M below the front and it then has a patio and steps and the garden 2M below low that. The house is only half as deep downstairs as upstairs, following the hill shape.
The lounge is at the back of the house and you go down stairs to get to it. She has started to see white mold under the stairs down to he lounge and as there is a trap door under the stairs I had a look under the floor. The ground below the lounge floor is about 1M below and dry and flat with various floor supporting walls with access points to get around.
There are underfloor vents at the side but the patio has blocked the vents at the back of the house.
Near one of the side walls there are two pits, about 1M wide and 2M long and 1.5M deep and these are wet filled with about 25mm of water. The underneath of the lounge floor is covered in white fury mould, though not the joists. I assume this is due to the high humidity under the floor and wondered what can be done to fix this.