Apartment vacancies in the Denver metro area fell to a 10-year low in the second quarter, dropping to the lowest vacancy rate since the first quarter of 2001, according to a report released Monday.

The vacancy rate fell to 4.8 percent with apartment vacancy rates falling 21 percent year-over-year from last year’s second-quarter rate of 6.1 percent, according to the Apartment Association of Metro Denver and the Colorado Division of Housing.

The vacancy rate was also down from 2010’s first quarter rate of 5.5 percent.

The study noted that the vacancy rate generally falls from the first to the second quarter because of seasonal factors.

“A vacancy rate below five percent is generally regarded as a sign that the market is tight,” said Gordon Von Stroh, a business professor at the University of Denver and the report’s author. “The vacancy numbers haven’t been lower than this since before the dot-com bust in Colorado, and that was a period marked by a scarcity of rental housing in many areas.”

Von Stroh said Monday that it has become increasingly difficult for people – especially younger people – to move into single family residences. Key factors, he said, are the unemployment rate, tightened credit and higher down payments.

He said there is a natural population increase in young people in the Denver area of about 35,000 a year. The first step for them is moving to an apartment. Because of the economy, they’re having to double up in many cases.

He said there also continues to be a large influx of people into Denver from out-of-state, many of them unemployed. The reasoning is if you have to be unemployed, what would be a nice option? The answer: Colorado.

On top of that, the lack of construction of new apartment units is not keeping up with the increased demand, sending the vacancy rate lower, he said.

“There is also a hesitancy because of the economy to move into single family residences,” Von Stroh added.

With vacancy rates declining, there has been a corresponding jump in median rents in the Denver area.

During the second quarter of 2011, the median rent in metro Denver rose to $863.37, increasing 2.5 percent from 2010’s second-quarter median rent of $842.70.

Ryan McMaken, Division of Housing spokesman, said that between 2002 and 2010, rents on average were flat. But now, said McMaken, there has been “some sustained growth” in recent quarters.

“However, in the year-over-year comparison for the second quarter, rents haven’t really kept up with inflation. The Consumer Price Index is up about three percent the past year, but the metro Denver median rent increased 2.5 percent.”

McMaken said that while “more desirable” rental communities have been able to push up rents significantly, in general many apartment owners have not been able to push rents “as much as they would have liked.”

Median rents rose in Adams, Arapahoe and Jefferson counties, but fell slightly in Denver and Douglas counties and the Boulder/Broomfield area.

The largest year-over-year increase in median rent was Arapahoe county which increased four percent from $806.11 to $838.79.

The largest decline was in Denver county where the median rent fell 1.6 percent from $814.14 during 2010’s second quarter to $800.94 during the 2011 first quarter.

Median rents were Adams, $863.85; Arapahoe, $838.79; Boulder/Broomfield, $969.13; Denver, $800.94; Douglas, $1,015.33; and Jefferson, $813.50.

Howard Pankratz: 303-954-1939 or hpankratz@denverpost.com.