We have a living room in the basement area of our house. It is furnished and a pleasant place to be, but the atmosphere feels a bit humid sometimes and I have found traces of mold on my woodwork and soft furnishings in certain parts of the room.
The room is 'tanked' underneath the plaster so it ought to be sealed. There are stairs down and a fanlight at one end, which gives a bit of light and a storage heater for warmth. Any advice is welcome!
Any underground living space is likely to have damp problems. Inevitably even with tanking, moisture is therefore likely to permeate the walls and floor of domestic dwellings, which aren't built to robust standards.
There are several issues: damp entering from outside the room, moisture caused by occupants breathing and a rather static atmosphere.
The storage heater will cause some air circulation but overall the air will remain rather still, whereas above ground level there will be windows, doors and through pedestrian traffic which stirs the air and moves moisture on.
If you don't have a dehumidifier you should get one. The typical cost has come down and you don't need a big machine although, it needs a good tank capacity for all the water it removes from the atmosphere.
You will be shocked at how much water gets extracted each day, but it will help save your wood, fabric, possessions and incidentally your health as you may be inhaling spores, which cannot be good for you.