Leaks and black mold led the city last fall to condemn Church Street South, a decades-old apartment complex across from Union Station. Now, one year later, roughly half of the 300 families living there have been relocated.

Landlord Northland Investment Corp. — the private developer that bought the 301-unit affordable housing complex in 2008 and attempted to redevelop it — began to move families out of their apartments in the summer of 2015 after the residents filed a lawsuit over upkeep. In December 2015, Northland announced that, to expedite the process, the federal government had allowed the company to distribute portable vouchers that would help pay for an affordable home of the family’s choosing.

But relocation has progressed slowly, and the target completion date has been moved from this September to next spring. As of now, 143 families remain onsite, said Rhonda Siciliano, regional spokeswoman for the federal Department of Housing and Urban Development, which works with the city and Northland to relocate residents. Meanwhile, roughly 70 families have found new leases with their vouchers and another 53 are in temporary housing.

“Ideally, we would have liked to have seen this process move faster,” Siciliano said. “We knew going into this that there would be challenges and that this process would take some time, especially given the tight rental market in and around New Haven.”

Jordan Yorks, marketing associate at Northland, did not respond to a request for comment Thursday evening.

For Amy Marx, an attorney at New Haven Legal Assistance Association who filed the lawsuit last year against Northland, the pace is unsurprising. Very few homes in the Elm City’s housing market meet federal guidelines for vouchers, a situation which creates a ceiling rental price and mandates that potential units pass a health inspection, she said.

Many tenants also lack access to transportation and English fluency that would otherwise expedite the apartment search. In other circumstances, landlords will be less willing to rent to families with the Section 8 vouchers, even though such discrimination is illegal, Marx said.

“A lot of barriers are being put forth by landlords,” Marx said. “There are also other barriers. For example, it’s very difficult for a single mom with no car to be shopping around New Haven for a rental apartment.”

In December, Northland also promised to replace all 301 affordable housing units at Church Street South by transferring the $3.1 million in federal housing grants it has been receiving to other New Haven landlords. This will subsidize the cost of apartments so that landlords can offer rent at lower costs to families in need of affordable housing. Though HUD was in touch last spring with a dozen landlords, none have officially agreed to participate, Siciliano said.

But these transfers will help ensure that New Haven does not lose more of its already sparse affordable housing supply, especially as developers begin to build new shops, offices and apartments between downtown and Union Station. The vacancy rate in the Elm City for all housing was, in 2014, one of the lowest in the country.

“It’s just critical to make sure that as Northland tries to proceed with its own development plans, that we do not forget the Church Street South tenants and the housing that was their homes,” Marx said.