The company will spend about $35 million to purchase and convert the building, Faulkner said.
The company's insulation is mostly used in the residential construction industry, and is sold under a variety of trade names including Guardian, Georgia-Pacific and Servistar.
Faulkner would not say how much workers will earn at the plant, but he said wages will be "competitive."
Company officials said the new plant was needed because of growth in their fiberglass insulation line. Guardian Fiberglass operates three other insulation plants in Albion, Mich., Mineral Wells, Mo., and Erin, Ontario.
Peter Walters, group vice president for the company, said Berkeley County was attractive to Guardian for a number of reasons, including the high-quality of the work force here and competitive electricity rates.
Guardian depends heavily on electricity to melt materials like sand and soda ash to make its insulation, Faulkner said.
Fiberglass insulation is just one part of Guardian's product line. The company also is a leading worldwide manufacturer of architectural and automotive glass, and a leading supplier of car exterior trim components.
A magazine about the company that was released Wednesday shows the company's architectural glass being used in a number of buildings around the world, from skyscrapers in New York to a futuristic-looking golf club in the United Arab Emirates.
The company began in 1932 as a small windshield manufacturer in Detroit, Walters said.
Dignitaries including Gov. Cecil Underwood and U.S. Sen. Jay Rockefeller, D-W.Va., welcomed the company to Berkeley County during an afternoon ceremony at the AT&T building.
Underwood said the state expects to announce more new businesses across the state this month that will create about 900 more jobs.
"We are serious about creating jobs here," Underwood said. "We are not just talking about it, we're doing it."
Guardian will not make any major alterations to the former AT&T building when it moves in, said Faulkner. Much of the preparation work will involve moving production machinery into the cavernous 700,000-square-foot building, Faulkner said.
AT&T built the building in 1974 to store cable, switching gear and and other products, officials said. Part of the warehousing operations were later moved to Charlotte, N.C., when AT&T built a new facility there, said Bob Crawford, executive director of the Berkeley County Development Authority.
AT&T left the building last December, Crawford said.