Arlington County officials are adding another layer to their planning efforts: history.

The Arlington County Board unanimously approved a Historic Resources Inventory of nearly 400 commercial, shopping-center and garden-apartment properties that have a historic significance in the county.

“For us, we have been moving for a few years towards more interest and value in historic preservation,” said Christopher Zimmerman (D), chairman of the county board. “That had not been the case in Arlington for decades.”

Referring to the redevelopment and preservation of Clarendon’s downtown, Zimmerman said, “Not only do we want to do a transit sector with transit-oriented development, but preserve the character of what was an old transit-oriented town 75 years ago.”

The inventory was created out of a 2006 Historic Preservation Master Plan of 10,000 historic homes and buildings throughout the county. The new listing compares the architectural and historical importance of commercial properties from the turn of the 20th century up to the 1960s and places them in several categories, such as essential, notable and minor.

The commercial properties, shopping centers and garden apartments are among “the most vulnerable historic resource types we have,” said Cynthia Liccese-Torres, a county historic preservation planner. About a quarter of the commercial structures in the 2006 index have been demolished, she said.

In order to prevent the loss of even more buildings, county staff said the listing will be used as a reference tool before developers and property owners spend money on redevelopment plans, said Michael Leventhal, another historic preservation planner. Until this effort started, preservationists would come into the redevelopment process near the end, he said.

The inventory will “encourage stewardship and integration of historic resources into plans,” he told the board at Saturday’s meeting.

Preservation and conservation tools and initiatives — such as educational programs, tax abatements or options to transfer density to a different property — will be drawn up over the summer and presented to the board this fall to implement the county’s plan.

“Having a list like that allows them to be proactive, and not reactive, and leads to thoughtful planning,” said Sarah Cooleen, director of community resources and outreach with Preservation Virginia.

Cooleen said that many people don’t see the value in mid-century modern buildings that make up Arlington’s “local fabric.”

“A lot of people don’t realize that buildings that are 50 years old and older are worth saving,” Cooleen said. The inventory will “put a mind-set out there that recent history is just as important.”

For example, Arlington County was the first to receive federal dollars to construct garden apartments to support the growth of federal workers in the District. Similar types of construction followed throughout the country.

Joyce Motors, located at 3201 10th St. North and built in 1949, is the last remaining example of a porcelain-enameled service station in the county. The Colonial Village Shopping Center, which was built in 1937, demonstrates the Federal Housing Authority’s rules for a self-sufficient community and is the product of the New Deal-program architecture.

Even though several people spoke in favor of the inventory, William B. Lawson Jr., a lawyer representing several owners of historic garden apartments, said his clients are concerned about their property rights if buildings they own are listed in the essential category.

“The concern is, against their objection, their property would be designated historic locally,” he said. He asked the board to include an owner veto to the designation.

Zimmerman said that the consideration of a local designation includes the property owner. Virginia property rights laws include “a lot of leeway for property owners,” he said.

The actual listing within the inventory does not affect property rights at all, he said.

Board member Mary Hynes (D) suggested adding a layer of oral history, possibly using the Tell Arlington’s Story project, to the inventory to “develop a very different body of knowledge” to the buildings.

“I don’t want us to drop the stories of individual people,” she said. Those stories “provide another kind of context.”