indoor-outdoor air leakage of apartments and commercial buildings

Before discussing the analysis, we present the raw data in more detail. Figures 5 and 6
display the building leakiness data, by function and construction type (similarly to Figure 2 and
Figure 3), but now using plotting symbols that distinguish the buildings by height and by
footprint area. From visual inspection, there is little evidence of a substantial relationship
between height and leakage, footprint and leakage, or building age (or year built) and leakage
(see Figure 8). Nevertheless, in addition to building categories we included footprint and height
categories in the statistical analyses.
Our main results, discussed below, concern multivariate analyses that consider all of the
available explanatory variables together, but we also performed some univariate comparisons:
1. For buildings with footprint area greater than or equal to 1000 square meters
(n=107), the geometric mean flow rate at 50 Pa was 4.5 L per second per square·
meter of building shell. For buildings with footprint area less than 1000 square
meters (n=160) the geometric mean flow rate at 50 Pa was 2.6 L per second per
square meter of building shell.
2. For buildings with 5 or more floors (n=26), the geometric mean flow rate at 50 Pa
was 3.3 L per second per square meter of building shell. For buildings with fewer
than 5 floors (n=241), the geometric mean flow rate at 50 Pa was approximately
the same, 3.7 L per second per square meter of building shell.
3. For buildings built in 1986 or later (n=131), the geometric mean flow rate at 50 Pa
was 3.8 L per second per square meter of building shell. For buildings built
before 1986 (n=136), the geometric mean flow rate at 50 Pa was approximately
the same, 3.5 L per second per square meter of building shell.
Multivariate analyses (i.e. including more than one explanatory variable at a time)
suggest that there may be effects associated with building footprint and height, but in no case
did the parameters associated with building age indicate the presence of a substantial building
age effect, so we excluded age from our main analysis. The lack of evidence for an effect related
to building age may be surprising, given that new single-family homes have become much
more air-tight over the past twenty years (Chan et al. 2005). However, there is little reason to
believe that airtightness in commercial buildings must increase just because single-family
residential airtightness increases: first, construction techniques for most commercial buildings
are very different from those for houses, and second, cost-conscious homebuyers have more
incentive to save than do cost-conscious business owners since less than 1% of a typical
company's payroll is spent on heating and cooling. Persily (1999) has previously noted that
although many researchers and laypeople, assume that commercial buildings have become more
airtight in recent years, there is no evidence that this is true. Our analysis suggests that, as
Persily suggests, commercial buildings from the 1990s are about the same, in terms of leakiness,
as those from earlier decades. Effects related to building age could also be difficult to interpret
to a variety of effects such as changes in leakiness (or mechanical ventilation rates) due to
renovations; shell or duct leakage that change with time due to degradation of caulking or duct
tape (an effect that might depend on both building design and construction details), and so on.
24