C022 -- Envelope Leakage of Individual Units in New U.S. Low-Rise Multifamily Buildings PDF

Envelope air leakage tests on new residential buildings are becoming more common in the United States as state energy codes and energy efficiency programs add testing requirements. For low-rise multifamily buildings the three most common testing approaches measure the following values: (1) whole building exterior leakage; (2) individual unit total leakage (i.e., to the exterior, other units, and common spaces); and (3) individual unit exterior leakage. This paper provides results of U.S. Department of Energy funded research that included measurements of total, exterior, and interior leakage of 274 individual units in 25 low-rise multifamily buildings in six states.

Only 33% of the individual units had total leakage values below the maximum allowed by the relevant state codes. The rate of compliance was 96% for exterior leakage. The average total leakage was 4.10 ACH50 for units in common-entry buildings and 5.13 ACH50 for garden-style (i.e., separate entry) units. A total of 49% of the units had a total surface-area-normalized exterior leakage rate less than 0.20 CFM50/ft² (3.65 (m³/hr)/m²); 62% were less than 0.25 CFM50/ft (4.57 (m³/hr)/m²); and 88% were less than 0.40 CFM50/ft² (7.31 (m³/hr)/m²). For units in common-entry buildings, the exterior leakage averaged about 30% of the total and units on the top floor of vented attic buildings had the highest percent exterior leakage. There was typically more leakage to common areas than to the outside. The median surface-area-normalized leakage to the common area was 0.52 CFM50/ft² (9.50 (m³/hr)/m²), which was seven times higher than the median of 0.072 CFM50/ft² (1.32 (m³/hr)/m²) for the adjoining unit leakage. For units in garden-style buildings (i.e., separate entries), the exterior leakage averaged 54% of the total.