BANGOR, Maine — The Maine Historic Preservation Commission has a few problems with the design plans for the Bangor Public Library’s renovation project, prompting the project’s architect to revisit parts of his design.

In a September letter to Jennifer Boothroyd of Bangor’s Planning Division, the director of the state’s historic preservation commission, Earle Shettleworth Jr., wrote that “the proposed new addition [a glass atrium to be added to the front of the library’s 1997 expansion] does not appear to be compatible with the existing historic building and its 1997 addition.”

Bangor Public Library is listed on the National Register of Historic Places as part of the Great Fire of 1911 Historic District.

Shettleworth cited “Standard 9” of the Secretary of the Interior’s Standards for the Treatment of Historic Properties, Standards for Rehabilitation, which states that “new additions, exterior alterations or related new construction will not destroy historic materials, features and spatial relationships that characterize the property. The new work will be differentiated from the old and will be compatible with the historical materials, features, size, scale and proportion, and massing to protect the integrity of the property and environment.”

The library held an open house Tuesday night during which Portland-based architect Scott Simons, whose firm has been behind more than a dozen library renovation projects in Maine, including the Portland Public Library, laid out his plans for the Bangor facility.

The design features a two-story glass atrium at the front of the library’s 1997 expansion. There, an eight-foot extended roofline juts out past the glass, and a third level of glass sits above that roofline. The atrium extends to the third floor to allow for more light and a view of the window arches. It allows for a view of the 1997 building’s facade, while still providing more open space for library patrons and tying the old and new portions of the library together aesthetically, Simons said. There also will be an extensive redesign of the interior layout of the building.

“At the most basic level, it’s going to make this whole library work better,” he said.

Shettleworth’s letter recommended that the proposed addition be reduced in scale and that the long 8-foot roof overhang be scaled back. The Maine Historic Preservation Commission doesn’t have regulatory or enforcement authority over projects, but can make recommendations to maintain the integrity of historic buildings if requested — as Bangor did — or if the project is federally funded. In the case of federally funded projects, if the commission’s concerns aren’t addressed, the federal Advisory Council on Historic Preservation might step in to review the project, according to Kirk F. Mohney, assistant director of the commission.

After the event, Simons said he planned to use the state commission’s recommendations to adjust his designs. He said he’s considering reducing the roof extension, and sloping or reducing the size of the third-floor portion of the atrium to alleviate some of Shettleworth’s concerns.

It’s not unusual for the Historic Preservation Commission to step in and recommend design alterations, especially when a building carries the sort of historical importance and architectural significance that Bangor’s library does, according to Simons.

Simons said he’s “absolutely taking the commission’s concerns seriously.” He said he has had multiple discussions with the commission since last month’s letter.

Simons first started working on the Bangor project six or seven months ago, and it has gone through several iterations since, being adjusted after meetings with the library’s building committee, according to Library Director Barbara McDade. Bangor’s historic preservation commission approved the project, but requested an opinion from the state as well because of the building’s importance, according to Simons.

The library is in the midst of replacing its century-old copper roof, an effort funded through a $3 million bond that voters approved in June. While undertaking that project, the library also decided to launch an effort to raise an additional $6 million, about half of which would go toward modernization of its interior and exterior, and the other half toward its endowment and contingency funds. Stephen and Tabitha King promised $3 million if the library raised the rest on its own.

Construction on the renovation is scheduled to start in the spring.