expression, noun
under the same roof; in the same house
Idiomatic expression meaning living together or sharing a home. Often used in contexts of family, cohabitation, or communal living.
親子が一つ屋根の下で暮らしている。
The parent and child are living under the same roof.
一つ屋根の下に集まった仲間たち。
Friends gathered under one roof.
同居 is a more formal term for cohabitation, while 一つ屋根の下 is an idiomatic, warmer expression emphasizing shared living space.
Literally 'under one roof', a set phrase from the components 一つ (one), 屋根 (roof), and 下 (under). The exact origin is uncertain, but it has been used idiomatically to mean sharing a home.