Many buildings work on the 'overcoat' principle - particularly if they are made of materials which will absorb water (without rotting) when conditions are adverse (i.e. the winter), and later re-evaporate the moisture when external conditions are warm and dry (i.e. summer). Buildings made of brick and stone are particularly good examples of this phenomena - particularly if the walls are thick enough to absorb enough moisture for the given climate.
Within structures it is admissable to allow moisture to accumulate under average conditions in the winter provided that under average summer conditions this is dissipated either to the inside or the outside or both.
What has to be avoided are constructions which under excessive conditions allow moisture to become trapped between impervious layers. The gradual build up of moisture will result in decaying materials and fixings and damage to decoration.
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