In older homes their is a lack of vapour barrier under the floor slab. The nature of concrete is that the material is porous and as such, moisture can permeate through the basement floor slab.
Problems in older homes with no vapour barrier
Offgassing from rotting wood and decaying organic matter add to the musty odor.
Mould commonly occurs in areas where wood framing and materials come in contact with the floor slab
Radon gas can build up in the basement area more readily with no vapour barrier present.