How to Install Window Casing for Vinyl Siding

In this video, This Old House host Kevin O’Connor adds window trim to vinyl siding with the help of vinyl siding installer, Richard Scalzi.

Steps for installing window casing

1. Unscrew and remove the storm window from the outside of the window.
2. Pry off the vinyl siding and J-channel from around the perimeter of the window.
3. Use tin snips to trim off the metal flashing covering the exterior windowsill.
4. Notch the vinyl windowsill with tin snips to fit the existing windowsill.
5. Nail the vinyl windowsill to the old wooden windowsill.
6. Glue a vinyl end cap onto each end of the vinyl windowsill.
7. Set vinyl casing against vertical side of window and scribe bottom end to match angle of sill.
8. Cut bottom end of casing with aviation snips, then install the casing against the window. Repeat to cut and install vinyl casing for the opposite side and top of window.
9. Cut two lengths of vinyl Colonial molding and install one on each vertical side of the window casing.
10. Cut another length of vinyl Colonial molding and hold it horizontally across the top of the window. Mark where the top piece of molding intersects the vertical molding at each end.
11. Slide an aluminum coping jig over the end of the molding and align it with the pencil mark. Scribe a pencil line along the edge of the jig. Repeat to mark the opposite end of the molding.
12. Cut along the coped lines with aviation snips.
13. Install the top piece of molding, snapping it over the vertical side moldings.
14. Cut and install new J-channel along the sides and top of the window.
15. Take the vinyl siding pieces removed earlier and cut them down to fit around the window.
16. Slide each siding piece into the J-channel and secure to house with roofing nails.

Tools