In St. Petersburg, Fla., close by Tropicana Field, an unusual structure is emerging from a construction site: a rental apartment building. The work in progress on the Fusion 1560, a 325-unit upscale project in one of the states hit hardest by the housing crisis, is a sign that developers of multifamily housing are tiptoeing back into the business. This year, real-estate investment trusts, or REITs, are expected to start close to $1bn in new multifamily projects, according to real-estate research firm Green Street Advisors. While that still is less than average, it is a significant increase over the $100m of development starts in 2009. Analysts caution that the increase in construction doesn't mean there has been an improvement in the business. Apartment vacancy is at a record and unemployment, essential to the sector's health, remains elevated. But operators are betting that limited new supply, combined with an improving economy, will lead to ideal market conditions nationwide starting in 2011 or 2012. From then until 2015, "apartment REITs may generate the best property net operating income growth that they've seen in a very long time, maybe ever," said Haendel St. Juste, a REIT analyst with Keefe, Bruyette & Woods Inc. To be sure, there are risks. Given the multiyear construction window, companies have to start now to be ready in time. If the economy weakens further and recovery is delayed, landlords may be forced to keep rents low or offer free rent to get leases signed. "There's an element of risk," said Andrew McCulloch, an analyst with Green Street. "But if you were to go back a year, the outlook is much more clear today. Their confidence level in that eventual recovery is much higher."