How to Make Steps for a Deck

Measure from the deck surface directly down to the ground at a right angle. Record this measurement as the total rise of the steps.

Divide the total rise by seven -- the ideal step rise, in inches, according to the International Building Code -- to determine the number of steps needed. A total stair rise of 44.5 inches from ground to the top of the deck floor, for instance, yields 6.35 steps. Round either up or down, as appropriate, for six total steps in this case.

Find the individual step rise for your stairs by dividing the total stairs rise by the number of steps calculated. Given a 44.5 inch total rise, for example, divide by 6 to obtain 7.416 inches. Rounded appropriately, each step is 7.4 inches above the previous step.

Record the step run necessary. The ideal run, per the International Building Code, is 11 inches and the rule of thumb states that the run plus the rise should result in between 18 to 20 inches. According to this formula, the step rise of 7.4 inches combined with a run of 11 inches is 18.4 inches -- well within the standard range for stairs.

Multiply the number of steps necessary by the step run to find the total stair run, which is the length the stairs extends from the deck. For a total rise of 44.5 inches and six steps with a run depth of 11 inches, for instance, the total run results in stairs extending from the deck 66 inches total -- a little over 5 feet.

Measure out from the deck to ensure you have the clearance needed for the steps to extend the distance required. While you may shorten the run or raise the step rise slightly, as previously performed, to decrease the total run, this makes steps steeper. Check local code to determine the minimum step run and maximum step rise allowed in this situation.

Calculate the length of the stair stringer required by applying the Pythagorean Theorem. Square the total rise and the total run previously found. Add both together and take the square root of the sum to find the stringer length necessary.

In the previous example, a total rise of 44.5 inches squared results in 1,980.25, and a total run of 66 inches, squared, yields 4,356. The square root of the sum is 79.60. Rounded up, the stringer length is 80 inches -- a little less than 7 feet long. Note that the stringer is longer than the actual total run.

Clamp a straightedge on a carpenter's square with one end aligned with the step run measurement and the other with the step rise measurement. The result is a guide for measuring the steps, with the step shape precisely mimicked.

Place the square at the beginning edge of a 2-by-12-inch board cut to the stringer length. Lay the square's legs across the board so the guide edge runs along the board edge and the rise measurement is at the beginning of the board.

Trace around the angle created by the square. Slide the guide down, aligning the rise with the run just completed, and repeat down the length. This creates a zigzagging design like the teeth on a saw blade.

Cut the outlined pattern out carefully, using a circular saw until you are near the inner portion of each step. Switch to a handsaw to make these cuts. Cutting into the stringer needlessly weakens the stringer significantly.

Lay the finished stringer on top of another 2-by-12 board and outline the stringer. Repeat for any other stringers needed; one stringer for every 16 inches of stair width provides strong support. Cut each stringer according to the guide. Make a final cut on the bottom of each stringer, removing the bottom 1 1/2 inches, to allow for the thickness of the first tread.

Mount each stringer to the deck with a framing anchor, according to the product instructions. Alternatively, nail stringers to the deck joists with 10d nails or use 1/2 inch bolts.

Cut the tread boards from your decking material or other suitable lumber. It's common on deck stairs to use two 2-by-6 decking boards for each tread, leaving a 1/4-inch gap between the boards, and overhanging the step below by about 1 inch, creating a "nose" for each step. This results in a tread depth of about 10 1/4 inches. For deeper treads, you can rip two 2-by-8 boards to equal width, again leaving a small gap between them for drainage. Deck stairs often do not have risers, the vertical board(s) at the back of each tread, but you can add them if you like, using decking material or other suitable lumber. Be sure to leave a gap between the riser and tread, to allow for drainage. Install the treads and risers (if applicable) using deck screws or corrosion-resistant nails.