A new era begins today for FM Global, the commercial-property insurance company that was founded in Rhode Island in 1835.

The company will hold a ceremonial groundbreaking for a new four-story headquarters.

“It’s a very big deal for FM Global,” said Steve Zenofsky, a spokesman for the Johnston-based company. “We haven’t done this since the early 1970s.”

Construction is about to begin on the 340,000-square-foot building, which is expected to cost about $60 million. It will be located on 93 acres the company owns off Central Avenue, adjacent to its existing headquarters. The project is expected to be completed by mid-2009.

The company owns a total of about 300 acres of land off the intersection of Central and Atwood Avenues. The current headquarters was built in 1973.

Since then, FM Global has grown to become one of the world’s largest commercial-property insurers. The $4.5-billion insurer employs 4,800 people worldwide and ranks 578th on Fortune magazine’s list of the country’s largest companies.

In Rhode Island, about 770 people work in the Johnston corporate office, and another 100 work at a research campus in Glocester. In Massachusetts, FM Global has a total of 900 employees at offices in Waltham and Norwood.

In late 2006, FM Global started looking for a new headquarters because it was facing the end of its lease. In 1984, the insurer sold the building to a real-estate firm, and then leased it back for 25 years. That lease is to expire in July 2009.

The company considered extending its lease and renovating its existing building; it looked at constructing a new headquarters near some of its other offices in Norwood; and it considered existing buildings within Rhode Island.

In the end, it settled on staying close to home. The new facility will be just 650 yards away from its existing one.

“Determining a convenient location for a new headquarters and campus, and being mindful of the needs of our 800 employees, were key factors in making our decision,” said Shivan S. Subramaniam, FM Global’s chairman and chief executive officer, in December, when the company announced its plans.

“Securing approval of our plans and cooperation from state and town officials also was important in our evaluation process and we are particularly appreciative of the support we received from Governor Carcieri and his staff as well as Mayor [Joseph M.] Polisena and our neighbors.”

FM Global sought and received a zoning change from the Johnston Planning Board to allow the company to build the headquarters. Beyond that, the company did not seek any considerations from the town.

State and local officials did help the company speed up the process of obtaining permits, according to the Rhode Island Economic Development Corporation. Within 48 hours of notifying the EDC that the company was looking for a new headquarters, FM Global officials met with the executive director of that agency, as well as the governor, the directors of the state Department of Environmental Management and Department of Transportation, the company said. State and town officials developed a plan for a coordinated and expedited review of the project, FM Global said.

Under the terms of an existing agreement with the state, FM Global may receive a sales-tax abatement for some portion of its proposed project, according to a spokesman for the EDC. In a 20-year pact approved by the EDC on Nov. 5, 1998, the company received a tax break for work done at its Glocester campus and its Johnston offices.

A deal with Allendale Mutual Insurance Co. granted the company a tax credit on equipment it acquired through the merger with Arkwright Mutual Insurance Co. and Protection Mutual Insurance Co. that created FM Global.

At the time, Rhode Island officials estimated the credit would cost the state roughly $60,000 a year, but the company agreed to increase its payroll enough to generate $500,000 in new state income taxes.

The insurer also invested $78 million from 2001 to 2003 to renovate and expand its Glocester research campus.

The new headquarters will be a glass and brick office building and a three-level parking garage. It will be located behind the AIPSO building and softball field on Central Avenue.

The company said the new building will make more efficient use of its space and is designed to allow for future expansion as business grows. It will be situated in a wooded setting and the grounds will resemble the existing park-like setting on Atwood Avenue, the company said.

The structure will be designed, constructed and operated as a “green building” and is expected to be LEED (Leadership in Energy and Environmental Design)-certified by the U.S. Green Building Council.

The current headquarters is not very energy efficient, Zenofsky said, citing its many windows, which allow a lot of heat to escape.

He said what will happen to the current headquarters after the company moves out next year has not been decided.

tbarmann@projo.com