noun
space above the ceiling; attic space
Refers to the area between the ceiling and the roof, often used for storage or housing wiring.
天井裏にネズミがいるみたいだ。
It sounds like there are rats in the space above the ceiling.
古い家の天井裏には、いろんなものがしまってある。
In the attic space of old houses, all sorts of things are stored.
Compound of 天井 (ceiling) and 裏 (back, reverse side).