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Air Quality and Health in the Home |
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Tuesday, 10 March 2009 |
There are thousands of tens of thousands of organic compounds that are commercially available and are used in the manufacture of products found in the home. In the past this was less of a concern because homes were not built tightly and air was continually moving through the home, diluting the toxins in the air. With homes built tightly, the amount of air changes in a home is considerably less, which allows the toxic compounds to build up in concentration. There are two equally important approaches to designing for a healthy home: the first is properly ventilating and filtering the air in the home; the second is avoiding materials that are manufactured with toxic chemicals that will off-gas to the home environment.
As discussed under ‘Ventilation’, The Living Home is designed to constantly change approximately one third of the volume of air in the home each hour. Air from areas in the home where odors and moisture are expected (the bathrooms, kitchen and laundry room) is mechanically removed from the home, exchanging heat with incoming fresh air. Some recommend higher rates of air exchange, but it should be remembered that this air must be heated a good portion of the year in Lethbridge, which requires energy. Lower rates of air exchange, with a good choice of construction materials and home furnishings is the general design approach we took.
Air Pollution
The three main classifications of air pollution in a home are volatile organic compounds (VOCs), combustion by-products; and biological pollutants. There are other classifications of air pollution that have been attracting more attention, including electromagnetic fields generated by the wiring and motors in a home, and naturally occurring pollution, such as radon from the soil.
Volatile Organic Compounds (VOCs):
VOCs may be naturally occurring or synthesized from carbon-based sources like natural gas, petroleum, or coal. The term ‘volatile’ suggests that the chemicals are released by substances (off-gassing) into the air.
Though there are tens of thousands of organic compounds, some common types of VOCs include products like xylene, toluene, styrene, formaldehyde, phenols, and acetone. They are found in products ranging from the adhesives used in plywood, OSB, and paneling; composite products using adhesives; paints, solvents and other finishes; carpets and underlay; insulation; cleaning products; and plastic/rubber products.
People react differently to VOCs in the air. Many have no apparent adverse affects to exposure, while others become very ill, and some people seem to develop symptoms over after a long period of exposure. Common symptoms include headaches, fatigue, depression, chronic sickness (cough and infections), and a tendency to have allergic reactions to an increasing number of substances.
Combustion By-products:
Energy sources burned inside the home like natural gas, heating oil, coal or wood produce heat for the home, and carbon dioxide and water as combustion products. Some more harmful by-products of combustion include carbon monoxide, nitrogen oxide, particulates, and hydrocarbons like methane, propane, pentane, benzene and xylene, among others, depending on the fuel source.
Common sources for combustion include gas stoves, and improperly vented furnaces or water heaters in the home. Another common source is the garage, when it is not properly isolated from the home. Incomplete combustion is a cause of many by-products, which can be avoided by proper maintenance, and pilot lights can be a constant source of by-products.
Symptoms of exposure to combustion by-products include depression, fatigue, and irritability. Chronic exposure to carbon monoxide interferes with the detoxification pathways in the liver allowing the accumulation of toxins in the body.
Biological Pollutants:
Biological pollutants may originate from outdoor sources, like pollens from flowers, flowering trees, bushes, and weeds which enter the home through the opening of doors, and through open windows. Biological pollutants may also originate from indoor sources, like molds growing where moisture accumulates in the home (in walls, bathrooms, windowsills, laundry rooms, etc.
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MERV Number
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Efficiency
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| 1 - 5 |
>20% |
| 6 - 7 |
20 – 30% |
| 8 |
40 - 50% |
| 9 - 11 |
50 - 70% |
| 12 - 15 |
80 - 95% |
Like many products, the more efficient the filter, the more expensive it will be. Regular replacement of filters is suggested for all types – once they are plugged, and ‘break through’ filters are no longer effective and they may cause blockage of air moving through the home.
Furnaces may also be equipped with air purifiers, which use ultraviolet light inside the ducting to sterilize viruses, bacteria, molds and other biological pathogens in the home. The lights consume a constant amount of energy and require replacement as they burn out.
The furnace and water heater must be properly vented to the outside. The combustion chamber is sealed in the furnace so combustion gases cannot leak into the home. Some furnaces will have an induced-draft blower to maintain a positive pressure inside the combustion chamber, blowing the combustion gases through the vent. Most furnaces are also equipped with electronic ignitions, replacing the pilot light.
Though many home owners prefer natural gas ranges and oven for domestic cooking, they can be a significant source of indoor air pollution. Electric ranges are preferable on the basis of air quality (though it may be argued that electricity is not a clean source of energy in many locations, like in the province of Alberta). If a gas range is used in the home, good ventilation is recommended.
Materials & Construction
Concrete:
Forms for concrete work are often coated with a petroleum-based releasing agent which adhere to the porous concrete. These releasing agents will off-gas for a period of time. This can be avoided by using insulated concrete forms (ICFs) which do not require removable forms, or by using non-rancid vegetable oil as a releasing agent.
If colors are to be added to the concrete, the type of coloring agent or admixture should be assessed to be free of off-gassing potential, as well as heavy metals.
Framing:
Kiln dried wood should be used in construction to reduce the growth of mold and discourage some insect pests. If treated wood is required, avoid creosote and pentachlorophenol preservative which are highly toxic. Borate-based preservatives and penetrating oils may provide adequate protection against insects and mold infestation.
Caulking and adhesives should be sourced as low VOC and non-toxic. Caulking is an important construction component to reduce water migration through the envelope and maintain a tight home.
Flooring and sheathing using plywood or OSB should be sourced with low-formaldehyde glues. The less volatile phenol-formaldehyde is considered preferable to urea-formaldehyde. Manufacturers are researching alternative adhesives that are formaldehyde-free. An expensive alternative is the use of solid wood for flooring and sheathing, or cement-based sheeting.
Insulation should be chosen to avoid moisture accumulation, which encourages mold growth in the home. It is very difficult to design a home that will not accumulate moisture in the walls with a variety of outdoor temperatures and humidity levels inside and outside of the home over a period of a year. Cellulose and fiberglass insulation tend to absorb water, which reduces their effectiveness and promotes mold growth. For a healthy home, foam insulation alternatives like Icynene™ and urethane should be considered.
Outdoor products like siding and roofing have less impact on indoor air quality than indoor products, but they can still be a source of contamination. Asphalt roofing systems, for example, are petroleum-based and will leach off with rain and melting snow. If this water is being harvested for irrigation, contamination could be expected. Concrete-based, slate or tile roofing is better for rainwater harvesting.
Finishing:
Medium density fiberboard (MDF) is commonly used for non-structural products like cabinetry and mouldings/baseboards. MDF is a wood product that commonly uses urea-formaldehyde adhesives. Some MDF products are better than others, and they can be avoided by using solid wood products.
Countertops can be made of composite wood/plastic products, sheet granite, tiles, wood, stainless steel, concrete, and many other materials. Porous materials like wood and grout between tiles may permit bacteria and mold growth, while composite products contain adhesives with potential VOC off-gassing. Some granite is radioactive and is not recommended for long-term exposure. A new product called IceStone is a durable, concrete-based product using recycled glass as an aesthetic aggregate and can be mechanically fastened to avoid adhesives.
Solid wood flooring a healthy choice for a home, and better for the environment if it is sourced as a FSC certified product. Underlay for the flooring is typically plywood, but can be substituted with tongue-and-groove wood or rough-sawn lumber. The selection of finish and sealant is especially important – there is no point in selecting a good material and covering it with a sealant with high VOC off-gassing. Alternatives include bamboo flooring, many originating from certified and sustainable growing and manufacturing processes. Cork or natural linoleum flooring may also be considered, though both should be sourced with appropriate adhesives, and sealants & finishes.
Carpeting tends to trap dust which is a mixture of mold spores, animal dander, and dust mites that feed off of the harvest leaving behind their fecal matter and remains. This does not include the chemicals and residues from the manufacturing process which have been related to a number of health problems. Carpets can be a significant source of VOC off-gassing, which may persist for many years, including formaldehyde, benzene, xylene, toluene, styrene, and 4-phenly-cyclo-hexene (4PC) which are linked to an array of health problems. Carpet backings have also been linked to health concerns and should be critically selected. Wool carpets can be a better choice if they haven’t been treated with mothproofing chemicals. Carpets should be avoided in moist areas in the home including the kitchen, bathrooms, and laundry room. If carpets are chosen in the home, they should meet or exceed the requirements of the Carpet and Rug Institute’s Green Label Indoor Air Quality Test Program (per LEED Credit 4.3)
Low-VOC paints should be selected. In general, it is the pigments that are the source of VOCs, so lighter colors are suggested. The paint industry has been making efforts to develop low-VOC paints in all color ranges. Green Seal is an organization that has developed an evaluation standard and criteria for paints, stains and sealants for VOC emissions, heavy metals and other toxic organic compounds. LEED has provided some acceptable limits for VOCs from architectural coatings (Credit 4.4).
Conclusion
The focus on indoor air quality and home health in design has been increasingly important. In essence, each product chosen in the construction, finishing, and furnishing of the home becomes the potential source of indoor air pollution or contamination affecting the health of the occupants. The field of healthy design is an emerging one, and good advice should be sought when selecting materials. One reference that we would like to highlight is “Prescriptions for a Healthy House: A practical guide for architects, buildings & homeowners” by Paula Baker Laporte, Erica Elliot & John Bant from New Society Publishers.
To conclude:
- Design a good heating and ventilation system with filtration and air purification.
- Maintain heating and air conditioning equipment (regular inspections, replace filters and UV lights)
- Install and maintain smoke detectors and CO monitors.
- Eliminate building materials, finishing products, and home furnishings that off-gas VOCs or contain other contaminants.
- Avoid artificial fragrances in the home.
- Substitute cleaning chemicals with natural products, where possible. Be critically cautious of eco-labeling. Store chemicals in a well ventilated room.
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