How to Trim Out Stairs

Inspect the stair stringer, the angled structural beam that supports the treads and risers, at the flat landing. Note the point where the top edge of the sloping stringer meets the horizontal floor; this is where the bottom edge of two pieces of trim will meet.

Take a 1-foot long piece of trim and place it on the flat landing. Extend the bottom of the trim 3 inches over the point at which the sloping stringer meets the flat landing. Trace a line along the top of the scrap trim with a sharp pencil.

Remove the trim, and place it on the sloping stringer so that the bottom edge is past the flat landing. The top of the trim will now intersect your first pencil line. Draw a second pencil line along the top edge of the trim in this sloped position. The two lines will be parallel to the flat landing and the sloping stringer. Using a ruler or straightedge, connect the point where the two lines meet to the point where the top of the sloped stringer meets the flat landing. The angled line you just created represents the cut line for both pieces of trim.

Test the angles by cutting scrap pieces of trim to see how they fit together before cutting the trim you will use on the stairs. Use two pieces of 1-foot scrap trim, and place one on the sloped stringer. Slide it up so the tip of the trim touches the intersection of the two pencil lines you drew.

Keep the trim in place and mark the bottom of the trim where the stringer meets the landing. Place a piece of flat trim on the floor, and use a straightedge and a pencil to create a line across the face from the tip of the trim to the mark you made at the bottom.

Put the trim into the miter saw. Lay it flat, and rotate the blade so that the blade becomes parallel with the pencil line. Make a precise cut on this pencil line. Use the same technique with the other piece of scrap trim placed on the landing. When you cut the second piece of trim, the two angled cuts should meet perfectly.