At the request of the Municipal Building Committee, the Community Preservation Committee voted Wednesday to contribute more than $1 million over the next 20 years to the cost of renovating Town Hall.

The vote was unanimous, though two voting members, Chairman Donald Boyce and Parks and Recreation representative John Lee, were absent. The result is the first show of financial support by any board or committee in town for the much-debated renovation of the 140-year old building, a project that the Board of Selectmen and the finance and capital committees have yet to approve.

New calculations released by the Municipal Building Committee last week estimate that bringing Town Hall into the 21st century will likely cost the town $4.1 million (without interest). This money will be borrowed and repaid by taxpayers in installments over 20 years, like a homeowner’s mortgage. At an interest rate of 4.5 percent, according a memo prepared by Town Hall for the preservation committee, those payments would add $320,150 to town taxes the first year of the loan, but that amount would decline to $176,083 over the next two decades.

The Community Preservation Committee, by its vote this week, agreed to pick up part of that tab: $95,000 the first year, declining to $52,250 its final year, for a total amount, with interest, of $1.4 million. These contributions equal less than half the total revenue received by the committee annually from a tax surcharge approved by the town in 2001 when it adopted the state’s Community Preservation Act.

Committee member Micelle Catalina argued Wednesday that property owners in town already contribute more than $200,000 to community preservation funds every year through the CPA surcharge. Tapping that existing revenue stream, she said, will reduce the amount of new money that has to be raised from residents. And the committee will be left with more than $100,000 per year for the preservation of open land, support for affordable housing, and the other goals set forth in its charter.

Before any money can be borrowed to pay for work on Town Hall, voters must first approve the project at Town Meeting in April and then again at town election. Should the proposal fail, no expenditure of Community Preservation money will occur.