Part of house for humble people — attic, essentially? (8)
I believe the answer is:
basement
'part of house' is the definition.
'humble people attic essentially?' is the wordplay.
'humble' becomes 'base' (both can mean improper or low).
'people' becomes 'men' (men can refer to humanity as a whole).
'essentially?' says to take the centre (I've seen 'essentially' mean this).
The centre of 'attic' is 't'.
'base'+'men'+'t'='BASEMENT'
'for' acts as a link.
(Other definitions for basement that I've seen before include "Japanese medicine box" , "space below stairs" , "Lowest floor of a building" , "Underground room" , "Lower ground floor" .)