The Department of Energy estimates that 70% of the energy lost in a home is due to air infiltration. The average american home exchanges all of its air 20-30 times per day. A energy efficient home exchanges air between 2.5 and 5 times a day. Spray foam is the best air barrier on the market today.You see spray foam expands 30 times it's liquid volume filling all the voids in the walls and roof. In fact these houses are so tight they require a fresh air intake mounted to the HVAC unit to bring fresh air in to the home. These units are very inexpensive and provide a way to pre filter air that is introduced to the environment. By filtering air you can take out 90% of the contaminates that are in the outdoor environment. This in unison with moisture control will stop mold from growing.
The American Lung Association says that asthma has increase more than 70% in the last decade. They believe this due to the fact that we spend more time indoors and our indoor air quality is worse that downtown Los Angeles. Spray foam, and a well planned HVAC system will improve the indoor air quality, that is why the ALA healthy house used spray foam.