A home should be a refuge; a safe haven. Homeowners should not be worried about the air they breathe in their own dwelling.
As builders, remodelers, and homeowners focus their efforts on energy efficiency, less fresh air leaks in. This, coupled with outdoor air that might not be too desirable anyway, impacts the quality of the air within homes.
Indoor air can be contaminated from many sources. Cooking odors are the most obvious, but many contaminants are odorless and go undetected by the human nose. The home's air may also contain excess humidity, dust, mold spores, chemical fumes, radon, combustion products from mowers running outside or furnaces running inside, and other potential irritants. Although most people aren't significantly affected by this indoor air cocktail, the long-term effects are still being evaluated. As anyone with asthma or other respiratory problems can tell you, poor air quality can become a serious matter.
Tech Set #9 covers the three basic steps that ensure a comfortable and allergen-free indoor environment.
Design and build the home to insure that it continuously performs properly.
Control the contaminants at their source.
Maintain the home and its environs.
Details: Indoor Air Quality Tech Set
Testing for many pollutants can be expensive, so source control is the preferred strategy, particularly in new construction. However, radon, an undetectable gas that can cause lung cancer at high exposures, is an exception to these high cost tests. Radon test kits can be purchased for as little as $9.95, placed by the builder or occupant to collect a sample under a controlled set of testing criteria, and returned to a lab for analysis.1 Where radon is detected or is likely to be present2 there are reliable, simple construction techniques that will mitigate the gas within the home.
Materials with Low VOCs - Eliminate VOCs, Formaldehyde, and Other Contaminants
Many conventional paints, finishes and glues contain high levels of VOCs (volatile organic compounds) that produce potentially harmful gasses when applied. Finishes that can give of VOCs include both stains and sealers as well as carpeting. Some building materials, like plywood and OSB sheathing and plastic-based products, also have high levels of VOCs. Many of the other named contaminants are detectable by occupants as odors or eye, nose, and throat irritants. Laminated wood products like sheathing, cabinet parts, and flooring are common sources of formaldehyde.The VOCs diminish air quality, and may be detrimental to your health.
To control the source of other air contaminants eliminate them by specifying materials (both permanent and decorative) that do not contain VOCs and/or formaldehyde. Today, low- and no-VOC paints and finishes are available almost anywhere, as are low VOC building products. They release no or minimal VOC pollutants, and are virtually odor free. This improves the indoor air quality of the home, making it particularly safer for people with chemical sensitivity. Also, latex paints use water as their solvent and carrier, allowing both easier cleanup and generally lower toxicity. Seal the surfaces with low VOC finishes or specify products that have eliminated these from the manufacturing process. For this process to be maximally effective, occupants must use the same diligence in selecting furnishings, carpet, draperies, cleaners, etc.3
Refer to Section 6. of EPA's ENERGY STAR Indoor Air Package Pilot Specifications for specific low VOC building materials and preparation and installation guides.
Ventilation, Humidity Control and Air Filtration - HVAC System Designed by a Professional
Surveys have indicated that occupants’ perception of good indoor air quality is highly related to thermal comfort4 so HVAC systems should be properly sized. System best practices are enumerated Tech Set #3, HVAC: Forced Air System. Specification references for sizing and installing HVAC systems while controlling ventilation, air infiltration and leakage is contained in Section 4 of EPA's ENERGY STAR Indoor Air Package Pilot Specifications.
Humidity control prevents the indoor growth of mold, mildew, viruses, and dust mites. Maintenance of an annual relative humidity range between 30-50 percent will control the source of many of these known biological contaminants. Winter humidification and summer dehumidification controls/modules can supplement central HVAC systems when climate excesses require additional conditioning measures.
Spot ventilation is a method of expelling moisture and odors that are regularly generated within a home. Fans in bathrooms and over gas-fired kitchen grills are examples of spot ventilators. When switched "on," fans remove the potential pollutant source while introducing fresh air by drawing it into the home through leaky areas of the building. This approach slightly depressurizes the house in the process of venting so it is sometimes referred to as an unbalanced ventilation method.
Unbalanced methods may provide adequate IAQ control for homes of many styles in many climates. Low sone (very quiet) fans are more likely to be used by an occupant. In-line fans can service several locations with seemingly- silent operation and greater energy efficiency. Fans can be wired to timers that provide a calculated level of air exchange.
Whole-house ventilators are integrated with the HVAC system to provide a measured amount of outdoor air to the inside unit for conditioning at regular intervals. Available systems range from a simple dampered air duct supplying outdoor air to an air handler to large intake/output units housing heat exchangers. These systems do not rely on air leaks in the home to deliver outdoor air.
All HVAC systems contain some method for filtration of the room air that is returned to the unit for re-conditioning. Filters vary by the size of particulates that can be trapped, ability to filter out moisture, and ability to sterilize micro-organisms (usually with ultra-violet light). Some filtration methods can be implemented by switching out the filter medium whereas others require an additional unit. Available high-efficiency whole-house air filtration systems claim to capture at least 99.7% of particles 0.3 microns and larger, and may be combined with activated carbon to absorb things such as cigarette smoke. Stand-alone room units can accomplish some spot filtration, as well.
Durable Building Envelope Details
A well built home repels moisture and air with good design features like covered entries, redundant barriers and grading that moves water away from the structure. Follow the steps outlined in Tech Set #2, Durable Building Envelope, to eliminate moisture intrusion
In homes with attached garages, it is particularly important to ensure the boundary between the home and garage is sealed properly. One study found that 75 percent of the benzene in the home environment is introduced from the garage.5 Air sealing the perimeter of a structure can make a significant difference in improving air quality inside the home.
Sealed Combustion Appliances
Heating equipment that burns natural gas, oil, or any other fuel that relies on an open flame within the home, should be vented to the outside by a sealed vent so that burning byproducts cannot backdraft into the home. Backdrafting is the movement of unwanted byproducts from burning like smoke, ash, and gases down the vent stack or through the appliance into the house. Backdrafting results from internal depressurization that can be caused by wind currents or unbalanced ventilation.
In addition to depositing chemical toxins like carbon monoxide in the home, backdrafting is a source for particulate matter (PM) - the term for particles found in the air that include dust, dirt, soot, smoke, and liquid droplets. PM can be inhaled and trapped in the respiratory system causing congestion and breathing difficulty. The size and range of particulate matter is shown in Figure 1 below.
Figure 1 - Particulate matter sizes of common household air substances.
Specification references for selecting and installing properly sealed combustion appliances are contained in Section 5. of EPA's ENERGY STAR Indoor Air Package Pilot Specifications.
The occupants of the home ultimately control the quality of indoor air long after good material specification and construction practices were employed in its construction. Particulate control starts with keeping outdoor contaminants out – practices like regular (out-of-home) washing and brushing of pets, insect and pest control, and wiping or removing shoes worn outdoors upon entering a home go far toward PM curtailment. Regular particulate removal via dusting, damp mopping and vacuuming is required to maintain a healthy indoor environment.
Without due care, occupants may introduce chemical contaminants with their selection of cleaning products6, furnishings7, and finishes. HVAC system maintenance and filter replacement should be performed at regular intervals. Smoking, using aerosol sprays and room fresheners, and candle burning should not be done inside.
The 2003 and 2006 International Residential Codes8 (IRC) specify that habitable rooms receive natural ventilation from outdoor air through windows, louvers, or doors with operable area that is a minimum of 4 percent of the floor area. Otherwise, a mechanical system providing .35 air changes per hour or 15 cubic feet per minute (cfm) per person may be substituted. Lavatories must have an operative window or ventilation of 50 cfm intermittent or 20 cfm continuously.
Jurisdictions that have adopted the International Mechanical Code of 2003 or a later version may require that newly-constructed kitchens be ventilated with outdoor air at a rate of 100 cfm intermittently or 25 cfm continuously.