Montgomery County commissioners voted Thursday to begin design on a $200-million-plus addition to the county courthouse and renovation of court and office buildings in Norristown.

Construction would be completed over the next decade, officials said, to address structural and security problems.

It would also focus the county's campus on Norristown's Main Street and Hancock Square, a park outside the courthouse. Norristown officials praised the plan, and said it could attract additional visitors and economic development to the county seat.

The three commissioners voted unanimously to support the plan, which could be adjusted and whose estimated cost is $233 million to $276 million.

Officials will study needs to determine how large an addition to build to the courthouse. The project would include security improvements; officials said the current courthouse has problems such as requiring prisoners and judges to use the same elevators.

Commissioners Chairman Josh Shapiro said work on a plan for the campus began when he took office in 2012 and received a report about the state of the county's One Montgomery Plaza office building.

The building "needs significant upgrades," Shapiro said.

The county considered selling the building and leasing space back, Shapiro said, but rent would have been too high to make financial sense.

Other options, presented to commissioners Thursday by Athenian Razak L.L.C., included renovating the current buildings and building a new courthouse at DeKalb and Airy Streets.

Renovating in place had an estimated cost of $178 million. Commissioners said that course would disrupt the workforce without significantly improving the appearance of the buildings or providing long-term improvements.

The estimated cost of building a new courthouse was $353 million. In addition to the cost, commissioners said they opposed moving the court and county employees a few blocks farther away from Main Street.

Commissioners kicked off the 10-year project Thursday by approving a $937,000 contract with Athenian Razak to begin planning and design for the first phase.

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