This article was originally published in the September/October 1998 issue of Home Energy Magazine. Some formatting inconsistencies may be evident in older archive content.


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Home Energy Magazine Online September/October 1998


Occupants Pollute Healthy Homes

Occupants of homes made with low-emitting building materials should take care to bring in only low-emitting products like this area rug from Hendricksen Natürlich.
It is common knowledge that living in a well-ventilated house can help a family be more comfortable. But how much can good ventilation help protect the occupants of a house against indoor air pollution? Canada Mortgage and Housing Corporation (CMHC) recently studied the topic and reaffirmed the fact that ventilation is of limited use in controlling levels of air pollutants in a home, as long as people keep bringing in polluting materials.

Researchers at CMHC evaluated air quality in six newly constructed houses. Five were of conventional design, and one was an R-2000 house. (R-2000 is Canada's nationwide standard for highly energy-efficient homes, much like the U.S. Energy Star program.) The researchers measured air quality levels just before occupancy, one month later, and after six months. Then they examined the relationships between three factors: volatile organic compound (VOC) emissions from building materials, emissions related to occupancy, and indoor air quality. Temperature and humidity were also monitored to see how they affected these pollutants.

Although emissions from building materials generally decreased during the first six months of occupancy, indoor VOC levels at six months were still more than 1 milligram per cubic meter (mg/m3). Building materials emitted pollutants at a rate ranging from very low, less than 0.05 milligrams per square meter per hour (mg/m2h), to very high, greater than 1 mg/m2h. The researchers attributed the residual VOC levels to a variety of possible materials and conditions, including oil-based paint on trim and doors, stained and sealed hardwood floors, and temperature and humidity levels. The study suggests that formaldehyde levels increase with temperature, and that VOCs weaken with decreased humidity. No less important are some common building materials such as carpeting, drywall, and cabinet board, which give off only moderate or low emissions but which cover large surface areas. Carpets, moreover, can soak up VOCs and re-emit them for many months.

However, while the overall rates remained higher than anticipated, the VOC emissions from these building materials comprised, on average, only 20% of the total indoor VOC levels at the end of the six months. After six months of occupancy, almost all pollution was occupant generated. Pollution sources included furniture, paints, cooking, smoking, and showering. The exception was formaldehyde, which mostly came from building materials.

There is no small irony when a household, presented with the chance to live in a relatively unpolluted environment containing low-emittance materials, moves in and brings along furniture, oil-based paints, and other items that emit VOCs faster than ventilation can carry them away. Under these conditions, ventilation is of limited use in controlling VOC levels. Normal ventilation rates cannot be expected to lower them below 1 mg/m3.

The small number of houses used in the sample precludes generalizations comparing conventional and R-2000 designs, but the study did arrive at some useful conclusions. The researchers contend that emissions from building materials can be controlled effectively only if builders use a minimum of adverse materials and the total surface area of major emission sources is limited. The report says this may prove difficult in practice because many materials, such as some brands of carpeting, do not meet low-emission criteria. In the absence of official low-emission labeling programs, it recommends that manufacturers should develop and supply low-emission materials on their own.

The results of the study also point out the need to educate consumers about pollution sources. This education is especially necessary for households that move into buildings constructed with low-emitting materials. Emission control is most valuable when the occupants of a house understand how their lifestyle affects indoor air quality.

The full report, Evaluation of Pollutant Source Strengths and Control Strategies in Conventional and R-2000 Houses, is available from the Canadian Housing Information Centre, Canada Mortgage and Housing Corporation, 700 Montreal Road, Ottawa, Ontario, Canada K1A 0P7. For research reports sent to U.S. addresses, send $10 (U.S.). Other foreign orders cost $15 (U.S.). For further information, call (613)748-2367.

-Gene Bodzin

Gene Bodzin, an Ottawa-based researcher and writer, has written on Canadian energy issues for more than 20 years.

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