“The growth rates in the industry are gargantuan,” Boorstein adds. The revenues for Public Storage increased 5.4% in 2014 and the other three REITs did even better. Extra Space, CubeSmart and Sovran all had revenue increases of more than 7.0%. In 2013, the same companies all saw revenue increases between 5.3% and 7.7%. “The increases in rents and revenue are unbelievably consistent.”

But even with all of this growth, new development remains relatively scarce. According to F.W. Dodge, there were only 78 new construction starts through the third quarter of last year, including renovations and alterations. However, Spencer Kirk, chief executive officer of Extra Space Storage, estimates that developers will launch between 300 and 500 new projects in 2015.

“That would not even match the rate of population growth,” Boorstein says. But based on the remarkable growth within existing facilities “we're sure this will pick up.” He points out that in 2005, the peak year for self-storage, developers delivered 3,665 new facilities.

“It's still tough to find good locations for self-storage sites,” he adds. “It's a retail business that operates in areas that frequently have industrial zoning, so you are limited in the number of good in-fill sites. It takes six months just to find a site.”

And once developers select a site, financing becomes the next hurdle. Whatever the occupancy levels in existing product, bankers still consider each new development, all of which open with zero occupancy, a speculative project, Boorstein says. Therefore, instead of establishing funds that could finance giant blocks of development in multiple markets, bankers approach self-storage on a deal-by-deal basis, further slowing down new construction.

But with demand so strong and new supply so muted, many institutional investors have become eager to jump into this sector. And according to the National Association of Real Estate Investment Trusts, “self storage has been the leading property type measured by average total returns, including dividends, over the past five-years, 10-years, and 15-years.” And in 2014, total average returns for self storage was 31.4%, trailing only multifamily at 39.6%, and ahead of retail at 27.6%.

Boorstein says the firm has had about 50 private equity meetings in the past year, roughly one per week, and expects a similar level of interest in 2015. “Everyone asks, 'how do we invest in this industry that shows no sign of stopping?' I've never been so optimistic.”