Chimney support's more uneven (7)
I believe the answer is:
lumpier
'more uneven' is the definition.
('lumpy' can be similar in meaning to 'uneven')
'chimney support's' is the wordplay.
'chimney' becomes 'lum' (I've seen this in other clues).
'support' becomes 'pier' (pier is a kind of support).
'lum'+'pier'='LUMPIER'
(Other definitions for lumpier that I've seen before include "more uneven" , "Having more bulges" , "With more large bits" .)