The number one alternative investment according to Bloomberg Markets is … storage space. Yes, you read that correctly.

According to the magazine’s annual ranking of alternative and exotic investments, storage units (specifically storage facility REITs) have been having a great few years.

Storage REITs such as Extra Space (EXR), Public Storage (PSA), CubeSmart (CUBE) and Sovran Self Storage (SSS) have seen gains between 142% and 483% in the past five years. Storage as a category has returned 101% from 2008 through 2011, outperforming all other REIT categories. There are now 52,000 storage properties in the United States, up from just under 20,000 in 1990. Nearly 11 million Americans rent storage units each year.

“Homeownership in the U.S. is at its lowest point in 19 years,” says Devin Banerjee, U.S. investing reporter at Bloomberg News, "and people aren’t upsizing [moving into larger homes] as much as they used to. if you’re not upsizing, then you need a place to put all of that stuff. You’re going into storage.”

Now that the economy seems headed toward recovery, however, it may be too late to get in on these gains.

“There are some warnings signs across the markets," he says. “The industry is consolidating, these large players are going into small towns, trying to expand geographically and acquiring local players."

“There’s a lack of new supply,” when it comes to storage space, Banerjee adds.