In the context of energy assessment, building ventilation specifically involves the supply of fresh air into a conditioned environment. Fresh air comes from the wider environment outside of the building.
It is important that all buildings have sufficient ventilation to ensure that the air inside remains of suitable quality for the building’s users. Too much uncontrolled ventilation results in a draughty building where heat is wasted. Equally, if a building is too air tight it can result in other problems commonly including damp and condensation.