Does Building Retrofit Program for Low-Income Households Really Create Healthy Homes?

Building energy retrofit programs have proliferated globally as key policy instruments for achieving carbon neutrality and addressing energy poverty. However, recent studies have raised critical concerns regarding the "ventilation paradox"—whereby improved airtightness inadvertently degrades indoor air quality (IAQ) by eliminating passive ventilation pathways. This repeated-measures field study monitored multidomain indoor environmental quality (IEQ) in 33 low-income elderly single-person households (mean age: 74.2 years, mean floor area: 42.3 m2) in Daejeon, South Korea, using IoT sensors for 25 days each before and after government-funded envelope retrofits (interior wall insulation and double-pane window replacement). Monitored parameters included thermal comfort, air quality (CO2, TVOC, PM2.5, PM10, formaldehyde), and acoustic conditions. Results revealed critical trade-offs: thermal performance improved dramatically (indoor-outdoor temperature differential: +267.5%, from 4.0 to 14.7°C), while all IAQ parameters deteriorated significantly—CO2 (+48.4%, 459→681 ppm), TVOC (+91.4%), PM2.5 (+90.9%), and formaldehyde (+90.0%)—with WHO PM2.5 guideline exceedance increasing from 12.1% to 42.4%. Notably, two contrasting objective-subjective discordances emerged: residents perceived improved air quality despite measured deterioration, while noise satisfaction decreased despite objective reduction (-14.9%) due to unmasking of previously inaudible neighboring sounds. These findings demonstrate that energy retrofits for vulnerable populations require integrated approaches including mechanical ventilation, low-emission materials, and occupant education to prevent the ventilation paradox from compromising healthy housing goals.