Building air leakage, or air tightness, refers to the resistance of a building envelope to inward or outward air leakages. There are a variety of different factors that can affect a building's air leakage, including external weather and internal building ventilation systems. Excessive air leakage increases the risk of spreading fire and smoke, energy consumption, and draughty and cold buildings. Improving building air leakage levels can provide essential protection from the spread of fire, deliver actual cash savings and enhance comfort for those residing in the building, whether inhabitants or, in the case of businesses, people who work within the structure.