In the last several years, a growing body of scientific evidence has indicated that the pollutant levels within homes can sometimes be higher than in outdoor air, even in large, industrialized cities. Other research indicates that people spend approximately 90 percent of their time indoors. The potential health effects from indoor air pollution vary greatly and range from allergies and asthma, to cancer and even death.
Indoor pollution sources that release gases or particles into the air are the primary cause of indoor air quality problems in homes. Inadequate ventilation can increase indoor pollutant levels by not bringing in enough outdoor air to dilute emissions from indoor sources and by not carrying indoor air pollutants out of the home. High temperature and humidity levels can also increase concentrations of some pollutants.
There are many potential sources of indoor air pollution in any home. These include combustion sources such as oil, gas, kerosene, coal, wood, and tobacco products; building materials and furnishings such as insulation, carpet, and cabinetry or furniture made of certain pressed wood products; products for household cleaning and maintenance, personal care, or hobbies; central heating and cooling systems and humidification devices; and outdoor sources such as radon, pesticides, and outdoor air pollution. The importance of any source depends on how much of a given pollutant it emits and how hazardous those emissions are, as well as the sensitivity of the population.
One component of maintaining good indoor air quality is the elimination, reduction, or management of the pollutant sources. Another important component is effective ventilation. If too little outdoor air enters a home, pollutants can accumulate to levels that can pose health and comfort problems. In the past, homes had a significant amount of "natural" ventilation from leaks in the building. However, because some weather conditions can drastically reduce the amount of outdoor air that enters a home, pollutants can build up even in homes that are normally considered "leaky."
Moreover, uncontrolled leaks can introduce moisture and humidity, pollens, and dust inside framing systems and interior spaces. This can lead to future air quality and durability problems. Beyond indoor air quality problems, leaky homes can be very expensive to heat and cool.
Building leaky homes isn't the answer. Tight energy-efficient homes save energy and money. And with proper mechanical ventilation, they can have better indoor air quality than a leaky home. The reason is control. In a leaky home, outdoor air enters the house — through cracks, unsealed joints, and penetrations, for example — intermittently, depending largely on the weather. Some times there will be too much leakage, resulting in a drafty, uncomfortable house. Other times there won't be enough, resulting in a stuffy house. Mechanical ventilation in a well-insulated, well-sealed house, however, can exhaust pollutants and bring in outdoor air in a planned way. This makes a house both comfortable and energy efficient.
While it may be difficult or prohibitively expensive to make some of the improvements described below with an existing home, building these features into an addition can be easy and inexpensive. You might even save money! And construction practices that promote good indoor air quality also help protect the house itself. For example, controlling moisture will reduce mildew odors, premature paint failure, rot, and structural damage.
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