How to Build a Stair Railing for Basement Steps

Hold the stair railing’s posts on the top and bottom stair treads, along the edge where you plan to install the railing. Trace around the edge of the posts where they contact the treads, and then place the posts aside.

Drill holes at the four corners of the tracings you did. Use a jigsaw to cut along the lines you traced, inserting the saw’s blade through the holes you drilled to begin cutting.

Insert the posts back through the openings in the stair treads. Hold a torpedo level along the side and then the top of each post to ensure it is plumb. Go under the stairs while an assistant holds the posts steady. Drill two holes near the bottom of the posts and through the side of the stairs.

Push bolts through the holes on the side of the stairs and through the holes in the posts. Go under the stairs again and slide washers over the bolts -- then tighten nuts onto the ends of the bolts, using a socket wrench, until the posts sit firmly in place.

Measure from the stair treads, up the posts to 36 inches and then mark the measurement on the posts. Position the stair rail against the side of the posts so the bottom end of the rail touches the line you marked. Secure the rail to the posts using wood clamps.

Mark where the edge of the stair rail touches the posts, and then unclamp the rail from the posts. Cut along the line you marked, along the bottom edge of the stair rail, using a handsaw. Place the rail on top of the posts, and drive two finishing nails through the top of the rail and into the posts.

Place one end of a baluster on one of the stair treads, positioning the baluster so it touches the side of the rail. Mark a line on the baluster where it intersects the bottom edge of the stair rail.

Cut the baluster along the line you marked, using a handsaw. Mark and cut the other balusters, using the first one as a template. Insert the balusters on the stair treads, so they touch the underside of the rail. Drive a finishing nail through the top of the rail and into each baluster, and a second finishing nail through the underside of the stair treads and into the other end of the balusters.