Trimming a window with T1-11 siding
I'm installing site-built non-opening wood window frames in a house with sheet 5/8" T1-11 siding (no sheathing underneath - the siding is the sheathing). I'm replacing the siding around the windows at the same time and I'm unsure about whether to fit the siding to the window rough opening, then install the trim over the siding, or to trim the window then fit the siding around that.
With the second option it seems like I would have better options for flashing, because flashing at the top could go under the siding at the top? The problem with this though is finding trim that extends far enough out from the siding after the siding is installed so that it looks decent.
Also, should the window frame (the box that holds the glass) be flush on the outside with the siding, and the trim installed over both the frame edge and the siding, or should the frame edge extend past the siding so the trim can butt up against it?