Cut the trim so it is two channel widths longer than the opening s width.
How to install window trim over vinyl siding.
Install the tops first then the sides and then the bottoms of the window surrounds.
Notch the vinyl.
Pry off the vinyl siding and j channel from around the perimeter of the window.
Install j channels at doors and windows and under roof eaves and rakes.
Along the tops install j channel trim with horizontal siding and base trim with vertical siding.
Exterior window trim on vinyl siding if your home has vinyl siding and you d like to add vinyl window trim you will first need to remove the existing siding and j channel from around the windows.
Place the piece of siding to be installed under the window along the bottom edge and hold it where it will be located.
Measure the distance from the inside top of the j channel to the locking tab of the course below and subtract 1 4.
Cutting and installing the siding 1.
Unscrew and remove the storm window from the outside of the window.