While inventories of homes for sale have been shrinking this spring, MLSs are filling the void with rental listings for single family homes that until recently were foreclosures. Some 16.1 percent of all listings on MLSs today are rentals, more than double the number in 2006.

Single family rentals are $3 trillion business today and growing as investors turn to real estate and opt to rent out the bargains they buy until prices improve. Today the single family rental market accounts for 21 million rental units or 52 percent of the entire residential rental market, according to a new study by CoreLogic economist Sam Khater.

Yet the single family rental market is poorly understood and almost invisible to economists and journalists because virtually all rental market data tracks multifamily properties and either ignores the single family segment or lumps it together with multifamily.

“Single family rentals are very distinct from multifamily and they behave very differently,” said Khater in an interview with Real Estate Economy Watch. For example, on a per unit basis, rents for single family rentals run 1.5 to 1.6 times higher than multifamily. Unlike multifamily, millions of single family rentals are listed on MLSs by real estate brokers, many of who represent new owners in acquiring investment properties. As the for-sale inventory has trended down since 2005, the rental share rose 13.3 percent last year alone. As of the end of last year rental closings were up 11.5 percent year-over-year while prices fell 9.8 percent during the year. Demand is strong. The national average months’ supply for single family rentals was 4.5 months in December compared to 6.2 months for homes listed for sale.”

Another important difference is the nature of the tenants. Single family rentals, usually stand-alone properties in ownership settings, appeal more to families. In fact, the typical SFR tenant is a family that has just left a foreclosure and can afford to pay the rent on a former foreclosure but could not make the mortgage payment on their old home, perhaps because they bought with alternative financing or purchased at the peak and could not get a modification when their home lost value. Over the past five years, foreclosures have turned more than 3 million homeowners into renters. Typical multifamily tenants, however, are younger, generally single and more mobile, and have never owned a home.

Khater found a strong relationship between distress sales markets and single family rentals. Census data shows a correlation between single family rentals and the hardest hit areas of the so-called “sand states”-Arizona, California, Florida and Nevada. Investors buying REOs and short sales in foreclosure markets convert them to rental units and homeowners in the same locale who have lost their homes to foreclosure rent homes that until recently were owned by other families who suffered the same ill fortune.