The Spanish Technical Building Code establishes the criteria for indoor air quality fixing minimum and constant ventilation rates per local. Currently, there is a proposal to modify the regulations so that the IAQ criteria becomes more useful by setting it based on average concentrations of CO2 and accumulated CO2 in the habitable rooms. However, the indoor average concentration is not the average concentration at which the occupants are exposed. This paper analyses CO2 concentrations, occupant exposures and occupants location inside dwellings according to the Spanish Technical Building Code change proposal. Legislation must continue advancing and adapting increasingly to the real needs of people and their protection.