It was supposed to be a five-year project.

That’s what architect Nima Yadollahpour, principal of ONY Architecture, and his wife, Shireen, an art educator, had planned when they purchased an antique 1,500-square-foot fixer-upper in Weymouth in 2004. “Weymouth was affordable,’’ Yadollahpour said, “and there was a master plan for Weymouth Landing just down the hill that indicated all sorts of ­development, including a new commuter rail station."