Fumigate to remove top-level mould in renovation, causing extreme tiredness (7)

I believe the answer is:

fatigue

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'extreme tiredness' is the definition.
(I've seen this before)

I don't understand how the rest of the clue works.

(Other definitions for fatigue that I've seen before include "Extreme tiredness" , "Tommy's punishment" , "listlessness" , "Tiredness after effort" , "Weariness, exhaustion" .)

I've seen this clue in The Irish Times.

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