Substandard housing conditions and hazardous environmental exposures indoors contribute to significant morbidity and mortality worldwide . Despite known adverse health effects associated with these conditions, most national surveys and housing indices do not include this information. Our study developed a national, multidimensional housing and environmental quality index (HEQI) informed by the WHO’s Health and Housing Guidelines and composed of ten healthy housing domains addressing structural deficiencies, indoor environmental exposures, and building conditions associated with adverse health. Using the 2019 AHS data, the HEQI identified approximately 92 million (79%) U.S. households with one or more HEQI risk factor(s). Compared to established housing quality and adequacy indices, the HEQI captured four new environmental health domains and at least 57.7 million (62%) more households at risk.
The multidimensional HEQI performed better than established housing indices at capturing both housing quality and environment health risk factors. Established indices focus primarily on physical deficiencies, costs of repair, or deflation in home values as a result of these deficiencies [11–13, 37, 38]. In particular, the PQI and Adequacy index underestimated approximately 61.4 million U.S. households with environmental risk factors like mold, cockroaches, household crowding, indoor combustion sources, and higher building leakage. Moreover, although prior studies have used the AHS to characterize environmental risk factors, most have focused on single AHS items like thermal comfort , air exchange , wood combustion , mold , and pests . To our knowledge, the HEQI is the first multidimensional index that captures a range of housing quality and environmental health risk factors.
Prevalent environmental risk factors identified by the HEQI and not well-captured by established housing indices were indoor combustion sources and dampness and mold. Indoor combustion sources include gas cookstoves, wood and kerosene heating fuel, and unvented fireplaces. These sources emit carbon monoxide, particulate matter, nitrogen dioxide, and other hazardous air pollutants that are associated with adverse cardio-respiratory health effects [46–48]. Approximately 72 million (62%) U.S. households reported the presence of least one combustion source indicator, particularly the use of gas cookstoves and fireplaces. Mold and damp environments were reported by approximately 18.7 million (15.4%) households, particularly water leaks from the roof, basement, and pipes, and mold in bathrooms. Mold spores can enter the indoor environment through building openings (e.g., doorways, windows, cracks, HVAC systems) and thrive in damp areas with excessive moisture, leaks, and flooding events [15, 44]. Mold triggers allergic symptoms, eczema, respiratory infections, asthma, dyspnea, and other pulmonary diseases [15, 49, 50]. Given that U.S. households spend approximately 87% of their time indoors , the risk of chronic exposure to these indoor hazards are high, and particularly in the wintertime and in cold climates when the building envelope is more sealed .
Our study found that the HEQI had good discriminant and criterion validity to capture unique dimensions of housing and environmental quality. The inverse correlation of indoor combustion sources with the building leakage domain reflects known trade-offs in indoor air quality and energy efficiency. In homes with frequent combustion-source activities (e.g., smoking, cooking, or candle/incense) and without proper ventilation controls, building airtightness can trap air pollutants and increase concentrations indoors. At the same time, high building leakage increases the risk of dampness, mold, pest problems, and energy loss [53–56]. Structural deficiencies can also lead to moisture and mold problems, physical injuries, openings for pests to enter the home, as well as energy loss resulting in lower indoor temperatures. As such, we observed positive correlations between the domains of dampness and mold with low indoor temperatures, lead paint risk, and injury hazards that are all associated with building structural integrity. Surprisingly, dampness and mold were not correlated with building leakage, which may be due to spatial imprecision of this indicator due to regional U.S. estimates and/or its coarseness as a binary indicator.
Furthermore, the HEQI was associated with measures such as unit rating, year built, and rent costs. Unit rating is a consumer rating index capturing residents’ perception of well-being and quality of life . In our study, risk factors strongly associated with lower unit satisfaction generally included those that residents were able to directly observe or experience, such as pests and allergens, lead paint risk, and injury hazards, consistent with previous study . Older housing has been associated with greater physical deficiencies and chemical hazards . While we could not evaluate chemical hazards, we found that older housing was strongly associated with deficiencies like inadequate water and sanitation, higher building leakage, and high indoor temperatures attributed to no central air or window air conditioning units. Rent costs is a market value index that assigns a monetary value to the quality of housing and neighborhood amenities, with higher rents suggestive of better quality . In our study, the modest associations between HEQI domains and monthly rent costs could be due to the omission of neighborhood amenities from our analyses . However we still found significant negative associations for four HEQI domains of pests and allergens, low indoor temperatures, injury hazards, and high building leakage. Additionally, severe crowding was significantly associated with higher rent costs, consistent with previous findings that cost-burdened residents report doubling-up to save on rent [2, 59, 60].
Our analysis also yielded findings that inform areas for future research. Indoor combustion sources and high building leakage were positively associated with higher unit satisfaction. Since we did not have direct measures of indoor air quality or building leakage, we used proxy measures such as appliance type (e.g., cooking, heating) and building features (e.g., unit size and height, basement and foundation type, year built). In effect, the positive associations may reflect residents’ preferences for these attributes instead of their understanding of potential health risks. Indoor air pollution levels and building ventilation are generally difficult to observe without the assistance of sensor technology . In addition, both of these domains have not traditionally been included in housing quality indices. Our findings underscore the need for further education among residents and housing practitioners about the sources of and strategies for reducing indoor air pollution and improving building ventilation.
We also found positive associations of inadequate water and sanitation with unit satisfaction and year built, which was primarily driven by the high proportion of households with non-public water sources (7.5%) (exclusion of this item switched the direction of the coefficient for this domain to be negative, data not shown). Non-public water sources have been attributed with a higher risk of waterborne illnesses [34, 35]. The positive association between non-public water sources and higher unit satisfaction may be attributed to suburban housing status, since suburbs that have a higher percentage of newer construction . Unfortunately, we were not able to investigate this given the lack of information about urban/suburban status in the public AHS data in recent survey cycles.
Next, we evaluate the application of the HEQI to AHS data and make recommendations for areas of improvement. Five healthy housing domains recommended by the WHO were not captured by the AHS due to the lack of data across survey years or in the full sample of households: radon, pesticides, asbestos, noise, and housing accessibility. These housing and environmental risk factors have been widely associated with adverse health effects (Table 1)  and should be ascertained in future national surveys. The four HEQI domains of dampness and mold, low indoor temperatures, household crowding, and inadequate water and sanitation were well-captured by the AHS and should be continued in future surveys to allow for longitudinal assessments. The remaining six HEQI domains, indoor combustion sources, pest and allergens, lead paint risk, high indoor temperatures, injury hazards, and ventilation, roughly approximated the underlying risks and were likely imprecise. In particular, the indoor combustion sources domain could be improved with more direct questions about the frequency and intensity of source activities such as cooking, smoking, candle us, incense use, and cleaning that can contribute to higher indoor air pollution concentrations . Questions about appliance efficiency, furniture and flooring types, and the types of ventilation controls like kitchen and bathroom exhaust fans are also important determinants of indoor air quality. For the pests and allergens domain, the AHS only asked about the presence and frequency of rodents and cockroaches. Future surveys should consider other types such as bed bugs and pet dander . For the injury hazards domain, only about electrical hazards and building integrity were collected in the AHS across multiple survey years. Information about smoke and carbon monoxide detectors, stairs and window railings, pool safety, and chemical storage have been asked in previous AHS cycles and discontinued in recent years or are only asked among a sub-sample of households. Going forward, these questions should be asked on a routine basis and among all households.
Our HEQI development has several limitations that could be addressed with improved data collection. The domain for high indoor temperatures was inferred from AHS items on central air and window air conditioning. High indoor temperatures could be influenced by ambient temperatures and humidity, which could not be ascertained in the AHS [32, 63]. Future surveys should include direct questions about heat stress (e.g., unit was uncomfortably hot for 24+ hours) and usual temperature in the home. The ventilation domain should include more questions about the types and performance of natural and mechanical ventilation controls (e.g., bathroom and kitchen exhausts, number of doors and windows, frequency of window opening). In addition, information about climate conditions, basement foundation type, and weatherization are needed to more accurately estimate building leakage. Lastly, routine data collection about energy efficiency (e.g., insulation, solar panels, Energy Star ratings) is important to track cost-savings and understand adaptation strategies for climate change.
The AHS data is also subject to limitations common to national surveys. AHS items were self-reported and may be susceptible to recall error or social desirability bias. The AHS survey design is based on a federally-sponsored in-person and telephone survey, which may underestimate households in precarious or temporary housing arrangements. These issues could impact the precision of our findings and/or underestimate the prevalence of the hazards identified. Lastly, the AHS is conducted predominantly in English and Spanish languages, which applied to 95% of households in the 2019 AHS data. Therefore, findings may not be generalizable to the small proportion of non-English speaking U.S. households.
In spite of these limitations, a major strength of the HEQI is its accessibility for widespread adoption. The HEQI is based on AHS data that is nationally-representative, publicly-available, and collected biennially by the U.S. Census Bureau. In addition, AHS items in the HEQI are available across survey cycles since 2011 and asked of all occupied households. Therefore, the HEQI can be used in longitudinal analyses to evaluate HEQI trends across U.S. households.