How to Build Stair Stringers

Lay the framing square on the stringer board so the unit run measurement on the outside of the wide body of the square intersects the edge of the board. Clamp a stair gauge on the inside edge of the leg so it won’t interfere with the marking. Set the length of the unit rise on the outer edge of the narrow leg so it intersects the edge of the board. Clamp on a stair gauge to hold the measurement. Mark the rise and the run for the first step at the top end of the stringer. Place the framing square on the board for the stringer with the gauges resting against what will be the top edge. Intersect the corner of the board with the rise line. The rise measurement at the top end of the stringer sets the stringer at the correct distance from the decking surface.

Extend the rise line to the bottom edge of the stringer. Mark an ‘X’ in waste areas to prevent confusion when you start cutting. Mark the rise and run for the next step. Slide the framing square down the stringer edge until the rise line touches the point where the tread line from the previous step intersects the board edge. Make certain the stair gauges rest against the board. Repeat this process to mark all steps. Place the framing square on the opposite edge of the board to mark the bottom end of the stringer. The stair gauges must rest against the board edge to maintain proper alignment. First extend the final rise line across the end of the board. Then mark a line the distance of the rise from the tread line on the last step.

Mark another line below the last line, at a distance equal to the thickness of the tread. This is the bottom of the stringer. Subtracting the tread thickness from the first riser will leave the first step up from the ground at a comfortable height. Start cutting the stringer at the top end of the extended rise line. Then make the top tread cut. Use a sharp blade in a circular saw to make crisp cuts with clean edges. When making the cuts, stop the saw blade just before it reaches the corner.

Complete the cuts in the corner with a jigsaw, cutting along the outside of the line to remove all the waste. Use the completed stringer as a template to mark boards for the remaining stringers. First hold the completed stringer in place to check for accuracy. Then clamp the template stringer to each board to keep the marking accurate.

If your closed stringers will be used in conjunction with open stringers, cut an open stringer first and use it as a template to mark the closed stringers. Position the template with the step corners set back from the edge of a closed stringer board by the thickness of the tread. Mark the tread positions on the closed stringer. Although you can also mark the rise lines, they’re unnecessary. You only need the tread lines for mounting the stair angles. Cut the extended riser line at the top end of the stringer. Then cut the bottom of the stringer to conform to the method you’ll use to attach stringers to the landing pad.

Install the stringers in their proper locations and fasten a stair angle at each tread location on the closed stringers. You could use 2x2 cleats instead. Attach a stair angle at each tread on the open stringers. Using stair angles on the open stringer provides an invisible connection. Install a stair angle on opposite side of the stringer, every other tread.

Drive fasteners recommended by the manufacturer (usually short lag screws) through the stair angles into the undersides of the treads. Use a ratchet and an appropriate-size socket to drive fasteners in spaces too small to use the drill.