This standard specifies practices, minimum requirements and general guidance for reducing soil gas entry into existing homes in order to mitigate occupant exposures to certain hazardous soil gases including radon gas, chemical vapors and other hazardous gases. This standard of practice is applicable to residential structures to include: those not more than three stories above-grade in height, those often classified as single-family structures, and those that contain not more than four attached dwelling units on a contiguous foundation. This standard of practice is applicable to existing homes be they rented or owned, including timeshare properties.