For the March meeting, Westcon member Bud Offerman will discuss the results of a 2005 mail survey which confirmed that many California homeowners never use their windows for ventilation. That study led to concerns that California residential building codes, which allow operable windows as a compliance path for ventilation, may result in homes that do not receive adequate ventilation for controlling indoor air contaminants. In response to these concerns, Indoor Environmental Engineering, a San Franciscobased IAQ building science firm, conducted a multi-season study in 2005-2007 of ventilation and indoor air quality in 108 new single-family detached homes in California for the California Energy Commission.
New California homes were found to be relatively airtight. Many owners never opened windows, especially in the winter months, and 67 percent of the homes had outdoor air exchange rates below the 2006 California Building Code requirement of 0.35 air changes per hour. Formaldehyde was the air contaminant that most frequently exceeded recommended exposure guidelines, with 98% exceeding the chronic irritation guideline, 28% exceeding the acute irritation guideline, and 100% of the homes exceeding California’s No Significant Risk Level (NSRL) for cancer.
The primary source of indoor formaldehyde emissions in residences is believed to be from composite wood products (e.g. particle board, MDF, OSB, and plywood), which are typically made with inexpensive formaldehyde-based resins, and are used in both home construction materials and home furnishings. Other indoor air contaminants that exceeded recommended cancer exposure guidelines included acetaldehyde, benzene, chloroform, 1,4-dichlorobenzene, naphthalene, and tetrachloroethene. Homes with continuously operated heat recovery ventilators (HRVs) performed well in increasing outdoor air ventilation rates and reducing indoor air contaminant exposures. Homes with simple outdoor air connections to the forced air heating/cooling systems did not perform well, as a result of low outdoor air intake flow rates and low fractional on-times.
This study concludes that mechanical ventilation systems are needed to provide a dependable, continuous supply of outdoor air to new homes, and reductions of variousindoor formaldehyde sources are also needed. This study helped initiate two important changes to California building codes and environmental regulations. The 2008 California Building Code now requires all residences to be provided with a mechanical outdoor air ventilation system.
In April 2007, the California Air Resources Board adopted an airborne toxics control measure (ATCM) to reduce formaldehyde emissions from composite wood products including hardwood plywood (HWPW), particleboard (PB), medium density fiberboard (MDF), and also furniture and other finished products made with these wood products. The future of residential construction will continue to emphasize tight envelope construction, but will also emphasize selection of building materials with low chemical emission rates, and incorporation of energy efficient mechanical ventilation systems.