When building an addition it is relatively low cost to rough-in for radon control. Garage exhaust fans help keep car exhause out of the house. Attached garages are also a source of indoor air pollution. Starting a car in the morning and turning it off at night releases many unburned gases in the exhaust. When the attached door is opened, the gases migrate into the house.
Carbon monoxide is a colorless, odorless gas that can be deadly.
A recent report indicated that 70 percent of carbon monoxide alarm instances were caused by car exhaust. An exhaust fan placed at the far side of the garage from the house door and wired to a timer that keeps it running for 10 to 15 minutes can significantly reduce the amount of gas reaching the house.