This is a case study of 13 Chicago metropolitan-area multifamily properties in which retrofits included air sealing and then insulating the roof cavities or attic floors using a blown-in fiber glass insulation. Fiber glass insulation is in the recommended category of insulations examined in Energy Efficiency for All’s report, Making Affordable Multifamily Housing More Energy Efficient: A Guide to Healthier Upgrade Materials.
For the 13 properties, the average gas energy savings was 18%. Gas energy savings ranged from 2% to 41%; the median was 17%. The subset of properties in which only the roof cavity or attic was air sealed and insulated realized an average gas energy savings of 17%. By comparison, a national study found that attic insulation and air sealing represented an average post-retrofit gas energy savings of 8% and 7%, respectively.
The national comparison further supports the observation that fiber glass insulation, specifically an insulation that contains lower levels of toxic materials as verified by third party designations, achieves effective levels of energy performance.