To help explain the ability of air to support water vapour below we have used what we loosely term the 'football' explanation.
If you imagine that a room is full up to the ceiling with footballs which for the purpose of this explanation represent air molecules. Because the footballs are round there are gaps in between them so if we now imagine these gaps are three quarters full of water this would be 75% relative humidity. Provided the footballs remain football size this water remains suspended in the air but if it came into contact with a surface that is below the 'Dew Point Temperature' some of this moisture would be deposited as condensation on that surface. So what causes this to happen?
When the footballs (air molecules) come into contact with a cool surface the footballs will shrink in size down to say golf balls or perhaps even marbles therefore the space between the air molecules is now much less than it was when they were footballs. So what do you think happens to the water previously suspended in the gap between each football?
At the surface where the cooling occurs, which may for example be a window, there is now insufficient space between the air molecules to suspend the water vapour thus the excess has to be deposited and this forms as condensation on cool surfaces often causing windows to 'steam up'. This same principle applies to any cool surface such as cold wall surfaces, the outside of a glass containing a cool drink etc.
Therefore if a property is heated adequately the 'footballs' remain large enough to support the water vapour load and wall surfaces become warmer meaning they are less prone to the formation of condensation. Stringent efforts should also be made to reduce the amount of water vapour in the atmosphere within a property thereby further reducing the likelihood of condensation forming.