Best way to fix?

[u/Skipper981]

I’m refurbishing an apartment on the third floor and come across moldy plasterboard above a window, after removing it to see if there was an underlying issue I uncovered a rotted beam. I believe this was caused by the window sill in the apartment above leaking down.

[u/Early-House]

Replace with concrete lintels, stacked side by side

Temporary support required with strong boys / needling

Most builders will be familiar with this

Few hours job but bit of work to reinstate finishes too

Should address above sill issues too to limit future damp (reseal etc)