The effect of weatherization on the microbiology of the residential built environment in Upstate New York

Background: Weatherization of residential homes is a popular retrofit procedure to improve the energy efficiency of older homes by reducing building leakage. Several studies have evaluated the effect of weatherization on indoor pollutants such as formaldehyde and radon. Few studies have evaluated the effect of weatherization on indoor particulates and microbial exposures. Objective: We compared the effect of change in building leakage on indoor pollutants and bacterial community in weatherized compared to non-weatherized residential homes. Methods: Nine weatherized and eleven non-weatherized single-family homes in Tompkins County, New York were sampled twice: before and after the weatherization procedures for case homes, and at least 3 months apart for control homes that were not weatherized. We measured radon levels, environmental conditions, and collected air, carpet dust, and floor surface samples to assess the indoor microbiome. Results: We found a significant increase in living area and basement radon levels of weatherized homes compared to control homes (p = 0.03, 0.019). The indoor microbiome also became less similar to the outdoor community after weatherization. Compared to the changes in ventilation rate, temperature, relative humidity, and occupancy, season was a more predictive measure of indoor bacterial concentration. Conclusion: Ventilation rate reduction from weatherization procedures led to an increase in indoor radon levels. However, it did not affect indoor particulate mass concentration, indoor airborne bacterial load, and have very minimal effect on the microbiome of residential homes. Changes in bacterial concentration are more sensitive to seasonal variations, whereas radon levels are more sensitive to ventilation rate.