Replace a Window that is Indented, or Not Flush with the Wall

Not all windows are flush with the wall. Some are indented in an inch or two. This means the standard flush fin window that overlaps the wall will not work because the window would need to sit deeper into the opening. 

In this case, the best method is to purchase a retrofit window with flush fins, and then cut the flush fins back to the width of the opening so the window fits inside, and the flush fins cover up the old aluminum window frame.