Learn how to remove and add replacement components to a rotten window sill
The problem we have here is a rotten jamb and a rotten seal. This is all superficial. It is not inside where the actual window is going to sit. What I will do is I will just cut out a portion, square off, and just do a fill in. What I do is I take caulking, fill in, and then screw it to the ceiling. I will do the same thing with this. I will cut it off where the rotten stops, piece it, and screw it in, ceil it in and cap it over. That is what is going to have to happen. If the rotten would have went into the jamb then of course it would be a different story and I would have to replace the jamb inside. This is all cosmetic and if it had went in past the structural window then of course it is a different story and you would have to replace the whole jamb but not in this particular case.