Population demographics are not the same between those moving in and those moving out. Immigrants tend to live more to a house/apt than Americans, so demand is not necessary rising just because population is.
According to the Census bureau here are the numbers for average household size in San Diego county
2000: 2.73
2006: 2.72
During this period …
The net population increased by 127,000 people
The net outmigration was about 100,000 people.
Therefore this included an increase of 227,000 people solely due to foreign immigration and birth. These are likely heavily weighted toward immigrants from Latin America and births of those with Latin-American heritage.
227,000 is over 10% of the county population. Yet, this large demographic shift results in less than 1/2 of 1% change in the size of households.
Therefore, the anecdotal observation that immigrants live more to a household is not reflected in actual data.
