This standard applies to all spaces intended for human occupancy except those within single-family houses@ multi-family structures of three stories or fewer above grade@ vehicles@ and aircraft. This standard defines requirements for ventilation and air-cleaning system design@ installation@ commissioning@ and operation and maintenance. Additional requirements for laboratory@ industrial@ health care@ and other spaces may be dictated by workplace and other standards@ as well as by the processes occurring within the space. Although the standard may be applied to both new and existing buildings@ the provisions of this standard are not intended to be applied retroactively when the standard is used as a mandatory regulation or code. This standard does not prescribe specific ventilation rate requirements for spaces that contain smoking or that do not meet the requirements in the standard for separation from spaces that contain smoking. Ventilation requirements of this standard are based on chemical@ physical@ and biological contaminants that can affect air quality. Consideration or control of thermal comfort is not included. This standard contains requirements@ in addition to ventilation@ related to certain sources@ including outdoor air@ construction processes@ moisture@ and biological growth. Acceptable indoor air quality may not be achieved in all buildings meeting the requirements of this standard for one or more of the following reasons: a. because of the diversity of sources and contaminants in indoor air; b. because of the many other factors that may affect occupant perception and acceptance of indoor air quality@ such as air temperature@ humidity@ noise@ lighting@ and psychological stress; c. because of the range of susceptibility in the population; and d. because outdoor air brought into the building may be unacceptable or may not be adequately cleaned.