Probably not condensation as that normally starts in the coldest room at the top or in rooms with high humidity ie bathroom/kitchens. Condensation is caused by warm air carrying moisture, warm air rises and is attracted to colder surfaces, when the two meet condensation appears. Rarely is low level dampness condensation or rising damp more likely to be debris in the cavity bridging the cavity or air bricks not ducted through to under the floor so venting the cavity. Mal was in before me, he's your best bet by far