Cover up altar renovated at home (9)
I believe the answer is:
tarpaulin
'cover' is the definition.
(I have seen 'protective cover' mean 'tarpaulin' so perhaps 'cover' could also mean 'tarpaulin')
'up altar renovated at home' is the wordplay.
'renovated' is an anagram indicator.
'at home' becomes 'in' ('I'm in' can mean 'I'm at home').
'up'+'altar'='upaltar'
'upaltar' anagrammed gives 'tarpaul'.
'tarpaul'+'in'='TARPAULIN'
(Other definitions for tarpaulin that I've seen before include "sailor's hat" , "[SHHET]" , "It provides protection" , "Waterproof canvas used as covering" , "seaman rarely required" .)