floor below; lower floor
Refers to the floor directly beneath the current one, or a lower floor in a building. Often contrasted with 上階 (じょうかい, upper floor).
See also: 上階
I can hear a noise from the floor below.
The lower floors of this building are used as a parking lot.
Compound of 下 (か, 'below') and 階 (かい, 'floor'). The reading かかい follows standard on'yomi.