Head architect, going over work on exterior gallery, rejects second-last design making written defence (8)

I believe the answer is:

apologia

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'written defence' is the definition.
(I've seen this before)

I don't understand the rest of the clue.

(Other definitions for apologia that I've seen before include "Written defence or vindication" , "Written defence of one's conduct" , "Formal defence of belief or conduct" , "sort of defence" , "Formal defence of one's actions" .)

I've seen this clue in The Irish Times.

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