Poor ventilation leads to poor indoor air quality.
Ventilation refers to the circulation of stale, indoor air being replaced with fresh (hopefully) air from the outside.
In the last several years, a growing body of scientific evidence has indicated that the air within homes and other buildings can be more seriously polluted than the outdoor air in even the largest and most industrialized cities across the US.
Your home has been designed to ventilate, whether through mechanical filtration that introduces fresh air from the outside and expels the polluted indoor air or through natural filtration that allows for the stale indoor air to seep out of cracks and crevices in the poor building design while “new” air is introduced through other cracks and air leaks in the building shell.
Poor building design that allows for uncontrolled air infiltration into your home can introduce elevated levels of molds and other biological contaminants while concentrating higher than normal levels of CO and other non-biological pollutants to levels that are not safe for the occupants. More times than not, the “fresh” outdoor air is filtered through attic and wall insulation allowing for dust and contaminates to become part of your indoor air. While most homes have spot ventilation in the kitchens and bathrooms to help reduce humidity and CO concentrations in those rooms, you must remember that for every cubic liter of air that is expelled through exhaust fans, another cubic liter of air is brought into the home…do you know where that air is coming from?
Most homes, unfortunately, use natural filtration caused by air loss/gain from leaky air ducts, poor construction design, and air gaps in the home (i.e. doors, windows, etc.). Natural filtration often introduces new contaminants into the indoor environment as the air often passes over attic insulation or through dust laden wall cavities before entering into the home. However, builders are employing better air sealing techniques and advanced home designes that require mechanical ventilation systems to filter outside air and to reduce energy loss by heating or cooling the air before entering the building.