Building Ventilation

Background

Ventilation, as defined here, is the supply of outdoor air to a building. Ventilation rates vary considerably from building to building and over time within individual buildings. The influence of ventilation rates on occupant health and performance will vary depending on features of the building, outdoor environment, and occupants. Throughout the normal range of ventilation rates encountered in buildings, increased ventilation rates are, on average, associated, with fewer adverse health effects and with superior work and school performance. There is also evidence that occupants of buildings with higher ventilation rates, particularly occupants of schools with higher ventilation rates, have lower rates of absence. The main findings of related scientific research are as follows:

Ventilation Rates and Office Work Performance

Performance (speed and accuracy) of typical office tasks improves with increased ventilation rate. For initial ventilation rates between 14 and 30 cfm (6.5 and 15 L/s) per person, the average performance increases by approximately 0.8% per 10 cfm (1% per 5 L/s) per person increase in ventilation rate. At higher ventilation rates, the average performance increase is smaller, approximately 0.3% per 10 cfm (5 L/s) per person increase in ventilation rate. For ventilation rates less than 14 cfm (6.5 L/s) per person, performance increases with ventilation rate seem likely; however, sufficient data are not yet available to confirm this hypothesis. 

Ventilation Rates and School Performance

The evidence of improved student performance with increased ventilation rate up to approximately 15 cfm (7.1 L/s) per person is compelling. Performance improvements with higher ventilation rates ranged from a few percent to more than 15%.

Ventilation Rates and Respiratory Illness

Substantially higher rates of respiratory illness (e.g., 50% - 370%) in high density buildings (barracks, jails, nursing homes, and health care facilities) have been associated with very low ventilation rates, presumably because lower ventilation rates are likely to result in higher airborne concentrations of infectious viruses and bacteria. Only a few studies have been performed.

Ventilation Rates and Absences in Offices and Schools

In one of three studies in offices, a 35% decrease in short term absence was associated with a doubling of ventilation rate from 25 to 50 cfm (12 to 24 L/s) per person. The other two studies of offices found no associations of ventilation rates with absence rates. Among five studies from schools or daycare buildings, four found statistically significant decreases in absence rates with more ventilation or lower carbon dioxide concentrations. The strongest study, which followed 162 classrooms for two years found a 1.6% decrease in absence for each 2 cfm (1 L/s) per person increase in ventilation rate.

Ventilation Rates and Health in Homes

The findings of research on how ventilation rates in homes affect health are mixed. Just over half of studies report one or more statistically significant health benefits of increased ventilation rates. Among studies that report one or more health benefits of increased ventilation rates, in most studies several other measured health outcomes did not improve with increased ventilation rates. Overall, however, the number of reported statistically significant improvements in health with increased ventilation rates far exceeded the anticipated chance improvements in health. The magnitude of the reported statistically significant improvements in health outcomes with increased ventilation rates were highly variable, ranging from 20% to several fold improvements. The research does not identify a threshold ventilation rate below which adverse health effects develop. Much of the published research has investigated the influence of ventilation rates in homes on asthma and related respiratory health outcomes. For other types of health outcomes, little is known about their dependence on home ventilation rates.

Ventilation Rates and Sick Building Syndrome Symptoms

Many studies have found that occupants of office buildings with above-average ventilation rates up to 40 cfm (20 L/s) per person have 10% to 80% fewer sick building syndrome (SBS) symptoms at work. A statistical analysis of existing data has provided a central estimate of the average relationship between SBS symptom prevalence in office workers and building ventilation rate. This analysis indicates a 15% increase in symptom prevalence as the ventilation rate drops from 17 to 10 cfm (8 to 5 L/s) per person and a 33% decrease in symptom prevalence rates as ventilation rate increases from 17 to 50 cfm (8 to 24 L/s) per person. The uncertainty in these central estimates is considerable. The most recent research suggest smaller effects of ventilation rates on SBS symptoms when there are low rates of pollutants emissions from the building fabric and building furnishings.