California's Ventilation Requirements

Ventilation Standards and Ventilation Codes

Ventilation standards are consensus documents published by professional or technical groups showing good practice. Government codes, utility programs, and private energy programs often cite national standards as part of their requirements. ANSI/ASHRAE Standard 62.2 is the national consensus standard on residential ventilation in the United States.

Ventilation codes are regulations with the force of law. In the U.S., no national ventilation code exists. Authority for regulating ventilation in buildings is left up to each state, and usually that authority is delegated to local jurisdictions (counties and cities). A code may require that a standard be met. California Title 24 Part 6 references ASHRAE Standard 62.2-2007 as California's state ventilation code, with one exception. Operable windows are excluded from the options for meeting whole-building ventilation requirements.

What Projects are Required to Meet ASHRAE Standard 62.2 Ventilation Standards in California?

  • All new residential construction
  • Alterations to existing buildings
  • Additions larger than 1,000 square feet (The ventilation system must be sized for the conditioned floor area of the entire dwelling, not just the addition.)
  • Federally funded weatherization projects

Additions of 1,000 sq ft or less are exempt from meeting the residential ventilation requirements.

A Simple Solution for Meeting Title 24 Ventilation Requirements PDF icon

Why is Mechanical Ventilation Required?

In the past, openable windows were considered an acceptable ventilation approach. In 2005, the California Energy Commission commissioned research on indoor air quality and ventilation in a sample of homes built in 2002 or later. One finding of the study was that Californians did not open windows often enough to provide adequate ventilation to keep indoor pollutants at acceptable levels. So mechanical ventilation is now required in California to improve indoor air quality in all new residential construction, when alterations are made to a residence, and in residential additions of 1,000 sq ft or greater.

Historically, ventilation in houses and apartment buildings was supplied by windows and random cracks and holes unintentionally left in the building envelope during the construction process. The number and size of openings varied with the builder, the building design, and the materials used. The movement of air wasn't planned or controlled, and the ventilation strategy for most builders could be summarized as "buildings need to breathe." However, this strategy causes periodic under-ventilation and over-ventilation, which results in potential unhealthy indoor air quality, wasted energy, drafty buildings, and movement of moisture into wall assemblies.

Ideally a ventilation system controls air movement and provides the highest volume of air when the need for ventilation is greatest. Unfortunately, a building's "breathing rate" through unplanned openings is dominated by weather conditions and the building's height. The largest volumes of air move in and out of a house when the wind blows strongly and the difference between inside and outside temperatures is the greatest. And higher volumes of air move in and out of a tall house or apartment building than a single story dwelling. Unplanned openings can also bring more polluted air into a building from undesirable locations, such as dusty or rodent-infested attics, moist crawlspaces, or attached garages where gasoline, fuel bottles, and pesticides are stored.

Relying on unintentional ventilation means the house will be under-ventilated and over-ventilated during part of the year, depending on the weather.

  • During cold weather and winter storms, low temperatures and wind will drive maximum air exchange rates, causing uncomfortable drafts and increased heating bills.
  • On hot days, when the AC is working overtime and outside temperatures are sweltering, unintentional ventilation brings in the highest volume of hot, outdoor air that must be cooled, increasing cooling costs.
  • Most climates have seasons when indoor and outdoor temperatures are similar. During mild weather with little wind, little air moves naturally in and out of a home. The level of indoor pollutants can rise, and inside air can become stuffy, stagnant, moisture-laden, and unhealthy.