Starts to renovate old cottage of church officer in an old decorative style (6)
I believe the answer is:
rococo
'an old decorative style' is the definition.
'starts to renovate old cottage of church officer' is the wordplay.
'starts to' suggests taking the first letters.
The first letters of 'renovate old cottage of church officer' is 'ROCOCO'.
'in' is the link.
(Other definitions for rococo that I've seen before include "Extravagant in style" , "Fancifully ornamented" , "Style of architecture, art, etc associated with the time of Louis XV" , "Elaborate late baroque style" , "18th century style" .)