This report summarizes a field study done in 108 new single family homes to investigate relationships between  home air exchange rates, window opening behavior and concentrations of various indoor air pollutants. The study concludes that new single family homes built in California can be very air-tight (median of 0.26 ACH), not meeting the California building code of 0.35 air changes per hour (ACH), and that the levels of indoor air pollutants in these new homes can exceed exposure guideline values. The report makes the following point:

• Home residents generally don’t open windows (especially if they are located in colder climates, or during winters) to get more ventilation air (confirmed by mail survey). Hence, relying on the residents for adequate ventilation is not an effective option.

As a follow‐up to the mail survey, a field study was then conducted to measure window and mechanical ventilation system use, outdoor air ventilation rates, sources and concentrations of indoor air contaminants (including amounts of composite wood and 22 different VOC concentrations measured for a 24-hour span), and occupant perceptions for multiple seasons and regions of the state. In addition, they measured the building envelope air leakage, garage‐to‐home air leakage, forced air unit duct leakage, window use, airflow rates, and fan system use. Results show that newly constructed homes in CA have:

• Very leaky ducts (86% homes exceeded duct leakage standards).
• Very air-tight envelopes (median of 4.8 ACH50, as determined by a blower door test).
• Most of the homes (65%) had garage-to-home air leakage higher than the American Lung Association standard (4 to 11% of garage air entering the home, confirmed by tracer gas study).
• Even in the homes that had mechanical ventilation with ducted outdoor air system, 65% homes failed to supply outdoor air exchange rates acceptable as per ASHRAE 62.2 ventilation standard. Instead, heat recovery ventilators are more effective outdoor air supply systems, with higher outdoor air supply rates
• 24-hour tracer gas studies in homes showed that 67% of the homes had outdoor air exchange rates below the minimum California Building Code requirement of 0.35 air changes per hour.
• Among the various indoor air contaminants tested, only PM2.5 and formaldehyde were found to exceed the recommended non‐cancer and non‐reproductive toxicity guidelines. Composite wood products were identified as the major emitter of formaldehyde. Levels of formaldehyde were highest in homes without mechanical ventilation, followed by homes with ducted outdoor air systems, and homes with heat recovery ventilator systems had the least concentration of formaldehyde. Indoor air concentrations of formaldehyde ertr found to increase with increasing air temperature and decreasing outdoor air exchange rate.
• The three most frequently reported symptoms were nose/sinus congestion, allergy symptoms, and headache.
• Summer window usage was significantly high compared to winter.

This project was completed by Francis J. Offermann, PE, CIH, Indoor Environmental Engineering, San Francisco, CA under Contract 500-02-023.