Costs and Benefits of Building Airtightness Improvements for Air Pollution Exposure and Human Health

Abstract

Air pollution is the largest global environmental health threat; fine particulate matter (PM₂.₅) alone, as the most harmful air pollutant, is associated with millions of premature deaths each year. Most studies focus on the impacts of changes in outdoor air PM₂.₅ on human health. This overlooks the fact that most exposure to PM₂.₅ of outdoor-origin occurs indoors, as people tend to spend most of their time indoors, and that the pollution infiltrates the building envelope. Specifically, Americans spend almost 70% of their time in their homes, and approximately 50% of outdoor-origin PM₂.₅ health burdens are due to residential exposure.

To better understand the effect of this infiltration on human health, and to explore opportunities for improvement, this study examines the health impact of enhancing building airtightness, particularly in single-family homes where approximately 75% of the U.S. population resides. This thesis conducts a historical study on modeled daily average PM₂.₅ levels between the years 1980 to 2010 in the United States to examine the national and spatial costs and benefits associated with improving the airtightness of these homes to mitigate the health effects of air pollution.

To achieve this, an integrated modeling framework was developed, which incorporates mass balance modeling, health impact modeling, and economic modeling. This framework was used to establish baseline and alternative levels of exposure to outdoor-origin PM₂.₅ across the historic building stock in the contiguous United States under the current state and post-intervention state. Subsequently, it evaluates the health benefits and retrofit costs associated with improving airtightness levels. The primary scenarios evaluated involve enhancing building air sealing to meet the standards mandated by the International Energy Conservation Code (IECC) 2018. Additionally, secondary scenarios of 20%, 25%, 40%, and 60% air leakage reductions were also considered.

This study analyzes the benefits of improving three distinct building age groups. The results reveal that enhancing the airtightness of single-family homes up to IECC 2018 mandates results in interventions costing approximately $105 ($102, $107) billion nationally. However, they could save about 44,611 (29,831, 58,905) lives annually and deliver annual health benefits valued up to $356 ($45, $1,173) billion in 2020 USD. The result is an annual net benefit of approximately $251 (-$62, $1,067) billion in 2020 USD, in the intervention year. This study also indicates that older homes, particularly those constructed before 1940, exhibit the greatest reductions in indoor PM₂.₅ levels from outdoor sources. These homes demonstrate a potential annual benefit of $55 ($7, $193) billion in 2020 USD and 7,104 (4,655, 9,832) lives saved, translating to about $3,066 ($390, $10,759) in 2020 USD in benefits per resident annually. On a per-house basis, the cost of improvements in these older homes averages $1,686 ($1,616, $1,756) in 2020 USD, while the net benefit per resident can reach up to $2,263 (-$442, $9,825) in 2020 USD in the year of intervention.

Significant spatial variability in benefits exists, with the greatest impacts observed in the eastern U.S. due to higher regional pollution levels and leakier homes. Further, there is uncertainty associated with model parameters, particularly associated with the health response to exposure. Despite these uncertainties, most interventions studied show large mean net benefits.

These findings strongly support that targeted enhancement of building airtightness substantially impacts public health and should be considered by decision-makers when designing building standards or developing retrofit plans.