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mitigation with increased outdoor air ventilation increases initial and operating costs <br />associated with the heating/cooling systems. <br />Further, we are not asking that the builder "speculate" on what and how much composite <br />materials be used, but rather at the design stage to select composite wood materials based <br />on the formaldehyde emission rates that manufacturers routinely conduct using the <br />California Department of Health "Standard Method for the Testing and Evaluation of <br />Volatile Organic Chemical Emissions for Indoor Sources Using Environmental <br />Chambers," (CDPH, 2017), and use the procedure described earlier above (i.e. Pre - <br />Construction Building Material/Furnishing Formaldehyde Emissions Assessment) to <br />insure that the materials selected achieve acceptable cancer risks from material off <br />gassing of formaldehyde. <br />Outdoor Air Ventilation Impact. Another important finding of the CNHS, was that the <br />outdoor air ventilation rates in the homes were very low. Outdoor air ventilation is a very <br />important factor influencing the indoor concentrations of air contaminants, as it is the <br />primary removal mechanism of all indoor air generated contaminants. Lower outdoor air <br />exchange rates cause indoor generated air contaminants to accumulate to higher indoor air <br />concentrations. Many homeowners rarely open their windows or doors for ventilation as a <br />result of their concerns for security/safety, noise, dust, and odor concerns (Price, 2007). In <br />the CNHS field study, 32% of the homes did not use their windows during the 24-hour <br />Test Day, and 15% of the homes did not use their windows during the entire preceding <br />week. Most of the homes with no window usage were homes in the winter field session. <br />Thus, a substantial percentage of homeowners never open their windows, especially in the <br />winter season. The median 24-hour measurement was 0.26 air changes per hour (ach), <br />with a range of 0.09 ach to 5.3 ach. A total of 67% of the homes had outdoor air exchange <br />rates below the minimum California Building Code (2001) requirement of 0.35 ach. Thus, <br />the relatively tight envelope construction, combined with the fact that many people never <br />open their windows for ventilation, results in homes with low outdoor air exchange rates <br />and higher indoor air contaminant concentrations. <br />10 of 19 <br />