How to Build a Three-Step Treated Stair Stringer

Measure the distance from the ground to the top of the stair opening, for a porch, patio or other structure. This is the total rise of the stairs. For instance, if the floor of your deck is 2 feet off the ground, the total rise is 2 feet. Write this figure down.

Divide the total rise by 3 to determine the step rise for each step on the stairs. A 2-foot total rise -- 24 inches -- divided by 3 steps results in an 8-inch step rise, for example. Record this figure.

Choose the step run you prefer. Local building code usually insists on at least 9 inches. A good rule of thumb states that the step rise coupled with the run should equal 17 to 18 inches total. Thus, in the given example of three steps spanning a total 2-foot total rise with individual step rises of 8 inches, a 10-inch run fits well, since 8 plus 10 equals 18.

Lay a pressure or chemical treated 2-by-10- or 2-by-12-inch board flat on a work surface. Since it's thicker, the 2-by-12 will prove sturdier. Inspect the board, flipping it over to look at both sides, to ensure it doesn't have knots, cracks or other structural defects.

Find the rise measurement on one end of a carpenter's square. Spread a piece of tape over the measurement line. Repeat with the run measurement, lining another piece up with the number line on the opposite side of the square. For example, the square would have tape lined up with the "8" for the rise and with "10" for the run in the previous example.

Align a short, thin straightedge with the outside edge of the tape at the rise and run measurement. Secure with tape or small clamps, attached from the large, open end of the square, to hold it firmly and precisely in position. When finished, the square and straight edge should look like a right triangle -- with an angle marked and the rise and run measurements blocked off exactly.

Lay the treated stringer board, wide side up, on your work surface. Align the guide board that marks the rise and run with the top of the stringer -- where the board will connect with the deck. The point of the square will extend onto the stringer board. Use a pencil to trace along both ends of the square. This will form your top step.

Slide the square across the board, aligning the beginning measurement with the last pencil mark of the previous step outlined. Trace along both sides of the square again. Continue down the board until four complete steps have been traced in a saw-tooth pattern; the top step will attach to the wood frame under the porch or patio. Alternatively, outline three steps if you prefer to attach the stairs to the outside of the structure.

Measure down from the last step marked to the rise measurement you are using. Lay the square across the stringer board and mark a line parallel to the previous run marks. Cut the board off along this line to provide a flat bottom for the stringer to rest on the ground. For example, if your rise is 8 inches, cut the board off flat 8 inches below the last run.

Mark the top of the board with a cut line. For stairs mounted inside the porch or patio frame, the cut line belongs after the third step, parallel with the step rise. For stairs mounted underneath the structure, the cut line is parallel with the step run and rises above the previous step the appropriate distance -- thus forming a hidden step, as detailed. Cut straight across.

Cut along the step cut marks using a circular saw. When you get close to the inside point of the cut, where the rise begins, stop. Switch to a hand saw and finish cutting to the point. Continue for each step outlined. When complete, the stringer looks like stairs without steps.

Set the completed stringer on top of the next stringer board. Trace along the board to transfer the guide to the uncut board. Repeat with any remaining stringers -- estimate one stringer per foot of stair width.

Attach the stringers in place. Nail the top of the stringer to the underside of the porch or patio where wood meets wood, such as to the joists and beams. Alternatively, attach angle brackets to the top of the stringer and secure to the side of the structure involved, following bracket instructions and placing at an appropriate height.

Nail boards across the stringers, using a 1-inch-thick or greater board. Cut the board to the proper width and secure to each stringer with two nails.