Integrated Evaluation of Energy Performance, Indoor Environmental Quality and Building Envelope Performance in Retrofitted Multifamily Residential Buildings

Energy retrofits in residential buildings can substantially reduce energy demand while enhancing thermal comfort and indoor environmental quality (IEQ). However, the interactions between these outcomes remain insufficiently documented, particularly in occupied multifamily settings where occupant behavior plays a significant role. This study presents an integrated pre- and post-retrofit evaluation of two two-story, multifamily townhouse-style buildings (14 apartments total) in Syracuse, New York, USA, combining in-situ monitoring with occupant environmental surveys. The whole-building retrofit approach includes highly insulated prefabricated exterior building envelope panels for improved thermal performance and airtightness at the walls, roof, and foundation, and high-efficiency integrated mechanical pod solution for heating, cooling, ventilation, and domestic hot water. Energy performance was assessed through power consumption measurements, showing a normalized 76% reduction in thermal energy use during the heating season compared to pre-retrofit levels. Continuous monitoring captured indoor air temperature, relative humidity, CO2, PM2.5 concentration, and envelope surface temperatures across multiple seasons. R-value characterization results indicated a post-retrofit mean effective R-value of 6.02 m2K/W, representing a considerable improvement. However, blower door tests showed only marginal increase in enclosure airtightness. Occupant surveys documented self-reported thermal comfort, perceived air quality, satisfaction with retrofit outcomes, and behavioral patterns such as window operation and thermostat use. Results indicated improved thermal stability, lower CO2 levels, and reduced heating demand consistent with measured energy savings. However, variability in reported thermal comfort highlights the continued influence of occupant behavior and individual preferences. This study demonstrates the value of integrating quantitative building performance metrics with qualitative occupant feedback to fully assess retrofit outcomes. These findings demonstrate the value of integrating quantitative building performance metrics with structured assessment of occupant experience to fully evaluate retrofit outcomes. Such an approach ensures that energy efficiency improvements are achieved alongside sustained enhancements in indoor environmental quality and user comfort.