Norwich ― For decades, buildings downtown and along Norwich Harbor and the riverfront have sat vacant, underused or blighted, blocked from development by federal regulations that require extensive floodproofing for buildings in designated flood hazard areas.

But over the past 5 years, city planners, historic preservation and economic development officials have worked to qualify these buildings for exemptions to Federal Emergency Management Agency’s requirement that if renovations cost more than 50% of the building’s value, they would need to be full flood proofed, which can be very costly.

Many of those buildings are appraised at relatively low values, because of their rundown conditions. So, even a new roof or windows and doors could reach the 50% threshold, Deanna Rhodes, Norwich director of Planning and Neighborhood Services told the City Council Monday.

Starting in 2017, Rhodes and former Norwich Community Development President Jason Vincent, the former Stonington town planner, started delving into FEMA historic designation exemptions. Exemptions were in place for buildings on the National Register of Historic Places or state historic registers.

But the two planners discovered that if Norwich created a Local Inventory of Historic Places, buildings listed would qualify for an exemption from the FEMA “significant improvement” floodproofing requirement. The buildings still would need to meet building safety code requirements, Rhodes said, but those are not as extensive as floodproofing.

The City Council Monday approved a resolution creating a Local Inventory of Historic Places with 11 specific properties listed, including six buildings on Terminal Way on the Thames River, a giant vacant mill at 132-176 Franklin St., a small mill at 31 Clinton Ave. two retail buildings owned by Thayer’s Marine and the main building on the 7 New Wharf Road junkyard property at Norwich Harbor.

City officials said they are excited that the new designation could make the properties attractive to potential developers, some for the first time in decades. NCDC President Kevin Brown said the designation “unlocks the potential” of the properties. Brown said there is interest in the Franklin Street mill, but the flood zone issue is a problem.

“The owners are interested in selling the property, and there have been a number of interested customers,” Brown said, “but at the end of the day, this very matter has been a barrier. This should help us. It doesn’t solve the whole problem, but it could help us match-make a buyer with the owner.”

Many of the properties also are in city Enterprise or federally designated Opportunity zones, qualifying for local property tax breaks or business investment tax credits.

Harbor Management Commission Chairman H. Tucker Braddock said the 50% improvement restriction has hampered interest in waterfront properties. He praised the city planning department for its “hard work” putting together the innovative program.

“It will encourage people to put money into some of these properties that are on the river edge, the floodway,” Braddock said. “The floodway is a real problem for us, as much as we can’t do that much with it. The Planning Department worked hard, found a glitch and opened it up so that people can put more money into some of these mills and some of these properties on the riverfront.”

Rhodes said she worked with Vincent, who had looked into the same issues in Stonington before coming to NCDC, to exempt the buildings, although they are not on the National Register of Historic Places.

“These are all really important buildings, and they’re in special flood hazard areas, but they’re not on national or state registers,” Rhodes said. “It doesn’t mean they couldn’t be on national or state registers.”

The planning department hired Regan Miner, executive director of the Norwich Historical Society, to research the histories of the buildings. Miner used the national register forms, so they would be “ready to go,” if an owner wished to pursue that designation to seek state or national historic tax credits for renovations.

Miner said she used old city directories and maps, as well as city land records and www.ancestry.com in her research and worked closely with the state Historic Preservation Office on the project.

c.bessette@theday.com