indoor-outdoor air leakage of apartments and commercial buildings

sample every county in California, although the Census Bureau intends to modify the survey to
do so in the future. The survey is designed to permit estimates of statewide statistical
distributions even though not all counties are included. The 2004 results estimate that there are
12 million occupied housing units in California, and another 800,000 unoccupied units (about
80% of them apartments). Most California housing units (58%) are single family detached
houses, and about 4.5% are mobile homes. The remaining 37.5% of housing units are in multiunit
structures, including duplexes, townhouses or row houses, and apartment buildings.
Table 4: Multi-unit or attached housing in California, by size of building.
Type of building Number of Percent of all Percent of nonunits
housing units single-unit-
(thousands) detached housing
units
I-unit attached 940 7 17
2 units 320 3 6
3 or4 units 720 6 13
5 to 9 units 820 6 15
10 to 19 units 660 5 12
20 or more units 1402 11 25
Table 4 shows the numbers of housing units that occur in buildings of different sizes. Excluding
single-family detached houses, about half of the remaining housing units are in buildings that
contain at least five apartments, and about a quarter are in buildings that contain 20 or more
apartments.
There is considerable variation in the housing stock between heavily urbanized areas and less
urban areas. For example, in San Francisco County (which contains San Francisco, California,
one of the densest cities in the country) 24% of all housing units are in buildings of 20 units or
more, and 45% are in buildings of 5 units or more. In contrast, in Tulare County, a rural county
south of Fresno, only 2% of all housing units are in buildings of 20 units or more, and only 6%
are in buildings of 5 units or more.
7.3. Gaps in Current Knowledge
The general lack of knowledge about building leakiness has been noted by previous researchers,
for both commercial buildings and apartments (Diamond et al. 1996, Persily 1999). Based on
available data, we cannot definitively answer even some basic questions, such as:
1. How many buildings of different types are leaky or extremely leaky?
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