In order to limit the energy demands the building ordinances establish requirements for reducing to acceptable levels the energy losses and/or gains. This situation obliges to define acceptable standards for thermal parameters. This report covered the evaluation of representative samples of Chilean homes built in 2007 and 2010 in the 54 provincial capitals of the country. A sample of 191 units was determined, representative of the construction, materials and housing architecture in Chile. Experimental techniques were used (Blower Door test) for obtaining air tightness of samples; numerical models (LBL Model) for relating the air tightness properties with the weather characteristics of every province in order to obtain infiltration coefficient classified by type of construction and province; simulation techniques (Thermal Analysis Simulation Software) for determining the energy demand of housing  The Air Tightness classes are established combining two criteria: the one that measures the current state of air tightness of housings and other that limits the infiltration demand to a limit value that explains itself economically.