The town’s Conservation Commission has reached an agreement with a private school to preserve the main part of a historic 1830s farmhouse that sits on its property. Under the agreement, Beacon High School can demolish additions to the Orchard House to create more open space, which it needs to meet state physical education requirements. Last summer, the commission blocked the school from tearing down the entire house, at 917 Belmont St., citing its historical and architectural importance to the town. Representatives from Beacon High, a nonprofit therapeutic school, previously said they tried to raise funds to restore Orchard House, but could not meet their goal. School and town officials have been meeting periodically to negotiate terms, and their agreement was announced at the commission’s meeting on March 14. The farmhouse dates to 1832, and was owned by succeeding generations of a prominent family with ties to the Boston Tea Party, Revolutionary War, and abolitionism. The Town Council still must approve the measure protecting the house as a historic site, Beacon High officials said.