Six Corner Board Details That Make Exterior Trim Look Finished

The Problem

Corner boards are where exterior trim decisions collide — deck skirts, siding, rooflines, and masonry all terminate against them, and every junction that wasn't planned shows up as a crooked reveal or a raw butt end.

The Techniques

1. Plan the flush-up at layout, not at trim time. When setting the deck ledger, step it back far enough that the skirt board and its overhang finish flush with the face of the corner board — that alignment can't be fixed later.
2. Rip matching stock from the same species. For cedar accents, ripping square stock from the same decking means every piece weathers and discolors together instead of two-toning in a year.
3. One-piece corner boards exist. Pre-assembled lock-mitered corners show no joint line and stay tighter than site-nailed two-piece corners — at a price (about $12.50 a foot in his case). An option to know about, not a requirement.
4. Keep wood off masonry. Where trim meets a chimney or concrete, use a PVC inside-corner piece against the masonry so there's no wood-to-concrete moisture transfer wicking into the trim.
5. Give the corner board something to die into. When the last real rafter lands short of the corner, add a fake rafter tail so the corner board terminates into it cleanly instead of ending in a bare butt end.
6. Fill dead space with a return. The awkward voids beside garage doors and similar spots close up with a simple trim return — a small piece that turns the corner and dies into the wall.