Bangor Savings Bank says it is spending $10 million to expand its presence in southern Maine.

The bank, which is headquartered in Bangor and is one of Maine’s largest community banks, said it plans to relocate its Portland branch at 280 Fore St. to 77 Middle St. and to renovate its remaining office space at 280 Fore St., which has functioned as the bank’s southern Maine headquarters since 2005.

The bank also is building a $5 million, three-story building at 20 Marginal Way, where a new branch will be located on the first floor with office and administrative space on the upper floors. In plans the bank filed with the Portland Planning Department in July, the cost of the Marginal Way building was estimated at $2 million. An additional $3 million will be spent on site improvements, furniture and equipment, bank spokeswoman Carol Colson said.

The new building will be outfitted with solar panels capable of producing more than 8,000 kilowatts of electricity, thus offsetting roughly 7,500 pounds of carbon pollution each year, she said.

The bank also intends to build a new branch in Brunswick. When complete, the expansion will bring the number of Bangor Savings Bank branches to 14 in York and Cumberland counties.

“Because of our growth and commitment to the state’s economy, and because of our work with Maine’s small business community, we anticipate there will be further expansion in this region,” Bob Montgomery-Rice, president and CEO of the bank, said in a news release. “We just learned that we have been named the top Small Business Administration lender in Maine for the fifth consecutive year. As this type of lending activity fuels the Maine economy, and our other banking services continue to expand, we look forward to announcing additional new branch locations as plans become finalized.”

The bank, which has $3.15 billion in assets, decided to move into the southern Maine market 10 years ago. James Conlon, the bank’s previous president and CEO, said it was a logical move for the bank because 75 percent of the state’s population was south of Waterville.

Despite the plan to add roughly 5,000 square feet of administrative space in Portland, Colson said Bangor Savings has no intention of moving its corporate headquarters to southern Maine.

“While we have a number of high-ranking executives in Portland and Bob Montgomery-Rice is spending one to two days a week there, our corporate office will always be in Bangor, where our history is,” she said.

To demonstrate the bank’s commitment to the Portland area, Montgomery-Rice presented checks to several local nonprofits at a news conference Thursday announcing the expansion. The bank is providing funds to grant two wishes to Maine children with life-threatening illnesses through the Make-A-Wish Foundation, along with an additional $5,000 donation. Montgomery-Rice also presented $5,000 checks to the Maine Cancer Foundation, Good Shepherd Food Bank, Maine State Society for the Protection of Animals and NAMI Maine.