Line house

A line house is a building deliberately located so that an international boundary passes through it. One such building on the boundary between the United States and Canada is the Haskell Free Library and Opera House in Stanstead, Quebec, and Derby Line, Vermont. The border is marked on the floor in a reading room and an auditorium. A number of single-family residences and some industrial buildings straddle the boundary in those two towns. 
The International Boundary Commission encourages line houses to be abandoned as part of its mandate to clearly demarcate the Canada–US border. The Haskell Free Library and most other line houses are on the Collins–Valentine line between Quebec and New York/Vermont.
Line houses exist also in Baarle-Hertog on the border between Belgium and the Netherlands,