UNDERSILL TRIM FLAGSTONE 12.5' VINYL | The CertainTeed Vinyl Undersill Trim helps provide a high level of finish with its color matching PermaColor Fade Protection. When installing under a window, soffit, or other projection it may be necessary to remove the nailing hem. Utility Trim replaces the nailing hem, helping to secure the panel to the wall. CertainTeed Undersill Trim will work with CertainTeed's Monogram, Restoration Classic, Board and Batten, Carolina Bead, Mainstreet, Wolverine American Legend, and Encore vinyl sidings.