BRAINTREE — The head of the state's school building agency said the town would likely lose out on $31 million from the state to build a new South Middle School if it the town doesn't come up with its share of the money.

Braintree resdients will head to the polls on March 28 to vote on a debt exclusion to build the new school as well as three other school projects.

Jack McCarthy, the executive director of the Massachusetts School Building Authority, told the town council Wednesday night that when a community rejects funding a project approved by the authority, "generally, that project is over."

He said communities that fail to pass a debt exclusion for a school project have 10 days to identify an alternative source of funds, but usually can't do so.

And, that means the community would have to start over in the highly competitive process for securing school building funds, McCarthy said. There are more than 100 statements of interest submitted to the authority each year and the authority is only able to fund about 10.

McCarthy pointed to the town of Lincoln, which rejected a project that had been funded by the authority. Now they are going forward with the project without authority funding. Not only have they lost the state money, but the cost of construction has gone up in the meantime.

The new South Middle School is part of a plan to expand the two middle schools to house grade 5 classes, to free up classrooms in the elementary schools. The first half of the project is underway, with the expansion and renovation of the East Middle School which is being paid for in part with $40 million in state school building aid. The town is slated to receive $31 million for the new South Middle School. School officials opted to go with a new building because it cost less than expanding and renovating the existing structure.

"I would hate to see this second half of the plan not get done," McCarthy said.

The debt exclusion seeks $86.5 million for the new middle school. The three other proposals on the ballot are for $5 million to replace roofs on the town's elementary schools, $1.5 million for a feasibility study for the redevelopment of Braintree High School and $1 million for security upgrades in school buildings.

A debt exclusion is a temporary tax increase tied to the life of a loan for a specific project, which would be for 30 years in the case of South Middle School.

If all four questions are approved, it would add 38 cents per $1,000 to the town's residential property tax rate, or an increase of 3.85 percent for the first five years. If all four debt exclusions are passed, an average Braintree home valued at $502,594 would see an increase of $191 to the annual tax bill.

Since Proposition 2½ was adopted in 1980 to limit property tax increases, Braintree has never passed a debt exclusion or override.

Fred Hanson can be reached at fhanson@patriotledger.com.