A non-drinker in charge of upper room (5)
I believe the answer is:
attic
'upper room' is the definition.
(room at the top of the house)
'a non-drinker in charge' is the wordplay.
'non drinker' becomes 'tt' (abbreviation for teetotaller).
'in charge' becomes 'ic' (abbreviation for 'in charge').
'a'+'tt'+'ic'='ATTIC'
'of' acts as a link.
(Other definitions for attic that I've seen before include "Ancient Greek dialect - top room" , "where high-ups are found?" , "of Greek region" , "Top storey" , "Room at the top of a house" .)