Board out
Definition 1 of 1
Pro Tip 1/3Casual Context
Used in informal discussions about living arrangements or real estate. 
My aunt is boarding out her flat while she travels this year.
Pro Tip 2/3Not Just Rooms
Can refer to renting out any living space, not limited to a single room. 
The couple plans to board out their entire house during the festival.
Pro Tip 3/3Income Implication
The phrase implies earning extra income from unused living space. 
Since the kids moved out, we're considering to board out their rooms.