Exposed beams and post (5)
I believe the answer is:
after
'post' is the definition.
(the prefix 'post-' means 'after')
'exposed beams' is the wordplay.
'exposed' means to look at the middle letters (the inside of the word is exposed).
'beams' becomes 'rafters' (rafter is a kind of beam).
The middle letters of 'rafters' are 'AFTER'.
'and' acts as a link.
(Other definitions for after that I've seen before include "Behind; seeking" , "Pursuing" , "back along > deck" , "In honour of" , "In pursuit of, behind" .)