Leaks from water and waste pipes (especially in bathrooms and kitchens) are relatively common. The can affect external and internal walls and ceilings. The affected area looks and feels damp to touch and remains damp whatever the weather outside.
A quick look at the pipes serving the kitchen and bathroom and the seals around the bath, shower and sinks, plus the external pipework (such as guttering) will usually find the source of the problem.
Note – Black mould is rarely seen on this type of dampness because this area is usually too wet and chemicals in a waste water leak will prevent mould growth