He estimated 11,000 homes in Las Vegas that are not owner-occupied. Many of them are being offered for rent because they're not selling.

"What we're experiencing is the amount of single-family homes being rented is giving us short-term supply. Ultimately, those homes will be sold," Ballif said.

He reported 7.83 percent vacancy for 100,218 apartment units surveyed in June. About 4,600 new apartment units are being built this year, he said.

Average rent for an apartment in Las Vegas was $876 in the second quarter, Novato, Calif.-based RealFacts reports. That's up 0.3 percent from $873 in the previous quarter and 3.3 percent from $848 a year ago. Average occupancy was 93.7 percent, compared with 93.9 percent in the first quarter.

Rents are sizzling in San Jose, Calif., and Seattle, where they increased 11 percent and 9.9 percent, respectively, from a year ago. Rents in Portland, Ore., grew 7.2 percent.

Previous annual rent growth leaders such as Phoenix, Las Vegas and Riverside-San Bernardino, Calif., continued to slide, Chris Bates of RealFacts said. With a quarterly increase of 0.3 percent, Las Vegas will see an annual rent growth increase of 1.2 percent, dramatically lower than last year's 5.4 percent annual growth rate, he noted.

"I think it's going to slow even more, particularly with decreasing occupancy," Bates said. "The other thing I've heard in pockets of California is all of these single-family homes are built and not sold, but they're being rented."

Carl Sims of Hendricks & Partners said the Las Vegas apartment market is changing.

"With Nevada having the highest foreclosure rate in the country for single-family homes and condos, we have seen the vacancy rate increase. This is surprising, but it seems the people being foreclosed on are moving into rental homes or upper-end apartments," he said.

Also, with home prices on the decline, some renters are now starting to buy foreclosed homes, he added.

Ballif of CB Richard Ellis said there's an upside and a downside to renting a single-family home over an apartment.

"You get more space, but you don't get a swimming pool, a fitness room or other conveniences. When something breaks, good luck getting ahold of the landlord," he said. "Those are choices people are facing."

Nevada has the highest apartment rent ($874) of four states in the desert region, RealFacts reports. Arizona ($779) is next, followed by Utah ($729) and New Mexico ($707).

Average rents in Las Vegas ranged from $606 for a studio to $1,075 for a three-bedroom, two-bath unit. Henderson rents average $986, North Las Vegas $907 and city of Las Vegas $860.

RealFacts reported 13 transactions this year involving 4,792 units with a total value of $483.1 million, or $100,820 a unit. Sims recently brokered the sale of the 178-unit Mountain Vista apartments in Las Vegas for $14.5 million, or $81,460 a unit.