屋根裏 屋根裏部屋
A room or a space immediately below the roof of a building.  Functionally serves the purpose of controlling the house's temperature by providing a large mass of slowly moving air.  Normally difficult to access, hot due to trapping the hot air rising from other floors, and hard to clean because of their irregular shapes, they're traditionally used for storage and considered undesirable residential spaces.

The term attic refers to a complete floor below the roof of a building.  For partial floors use the [[loft_(architecture)|]] tag.
attic