Change nails at first in defective rafters (8)
I believe the answer is:
transfer
'change' is the definition.
(I know that change can be written as transfer)
'nails at first in defective rafters' is the wordplay.
'at first' indicates taking the first letters.
'in' indicates putting letters inside.
'defective' indicates anagramming the letters.
The first letter of 'nails' is 'n'.
'rafters' anagrammed gives 'trasfer'.
'n' put within 'trasfer' is 'TRANSFER'.
(Other definitions for transfer that I've seen before include "Extremely stiff in coach, I must leave conveyance" , "handover" , "Change to another group or surface" , "Star fern (anag.)" , "player's move" .)