De Gannes-Cosby House, National historic site in Annapolis Royal, Canada.

The de Gannes-Cosby House is the oldest wood-framed building in Canada and the oldest surviving Acadian-style building in the world. Built in 1708 on the foundations of a house destroyed in the 1707 Siege of Port Royal, its core is wattle and daub, later covered in wooden shingles and enlarged in the 19th and 20th centuries.

Construction began in 1708 as a residence for a French officer during the early colonial period in the region. The building endured subsequent changes and has shaped the historical landscape to the present day.

The house is the world's oldest surviving building in the Acadian style, and its name links two families: the French officer Louis de Gannes de Falaise, who built it in 1708, and Major Alexander Cosby, lieutenant-governor from 1727, whose son, Admiral Phillips Cosby, grew up here. The current owners have advocated for its place in Acadian, Nova Scotian and Canadian history.

The house is a private residence and is not open for tours; visitors see it from the street within the Annapolis Royal Historic District. It received its National Historic Site plaque only at a dedication ceremony on 19 August 2023, delayed from its 2019 designation by COVID-19.

The interior walls still display the craftsmanship of early builders, such as visible timber framing and traditional infill techniques. These construction methods are typical of French building practices of that period and rarely remain intact.