Cut the trim so it is two channel widths longer than the opening s width.
How to install vinyl siding trim around window.
Cutting and installing the siding 1 place the piece of siding to be installed under the window along the bottom edge and hold it where it will be located horizontally along the wall.
Install j channels at doors and windows and under roof eaves and rakes.
Cut 5 inch strips of flashing that are 2 inches taller than the window and will overlap the bottom flashing by 2 inches.
The 5 inch wide flashing should slide right under the nailing fin on the window.