Rotten purlin under velux window

[oscarthecat91]

I am in the process of stripping back the attic rooms in my 1910 Edwardian terrace house which has been over boarded badly with no insulation.

Upon removing the boards I have discovered the middle section of the purlin under the velux window has rotten (presumably from a leak). It is the top tenth of this section of purlin that has rotted under the window - the rest of the length appears ok.

What is the best way to go about fixing this? There is no sagging in the roof or anything at present.

 

[blup]

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[Evren]

how long is the purlin ?
I am no expert but i does not look all rotten from the photos . Perhaps strip the paint and have a better look.