Mayor Martin J. Walsh pledged Tuesday to bring the city's deteriorating public schools into the 21st century, but he warned that the effort won't be cheap.
"You're probably talking over a billion dollars," Walsh said at an event at the McKay K-8 School in East Boston. "That's just a rough estimate."
Walsh said 65 percent of Boston school buildings were constructed before World War II, and fewer than half have been renovated.
The event Tuesday marked the formal launch of a 10-year master plan for Boston public schools facilities that Walsh announced in his State of the City address in January.
The School Department and the city are set to work with consultant Symmes, Maini & McKee Associates to develop recommendations by the end of 2016.
"It's going to be our first comprehensive school capital plan in 20 years," Walsh said. "It's going to be going beyond reactive maintenance. It's going to give us proactive strategies and [a] framework for success."
Walsh acknowledged that it would be necessary to close some schools to "unlock more resources for every student. Access and equity is at the forefront of our concerns."
Walsh said nothing is decided, but he expects some schools will merge under the plan.
"It's going to be controversial in some ways, but it's going to be the right thing to do to make sure that our young people get the best education, in the best buildings, with the best principals and the best teachers in this city," he said.
Some of the plan's expense, Walsh said, will be offset by "key funding partners."
The project will examine every space in every city school, he said, and find ways to make them compatible with contemporary needs for prekindergarten spaces, special education programs, and students learning English.
Walsh noted that improvements are underway at the Eliot K-8 Innovation School, Boston Arts Academy, and the Josiah Quincy Upper School. In Roxbury, a state-of-the-art facility is planned for the Dearborn 6-12 STEM Early College Academy.
Before the announcement, city and School Department officials toured the McKay School, seeing firsthand the windowless basement reading room that serves in place of a library, and the auditorium/gymnasium where gym teachers use the stage as office space.
Superintendent Tommy Chang praised the school for its "great use of its limited space."