Guide to Proper Construction of Deck and Porch Steps or Stairs

Measure straight down from the floor of the deck or porch to the ground. Change this number to a small scale and draw a line vertically along a line on a piece of graph paper to represent this height. For a 4-foot height, for instance, use a 1-inch per 1-foot scale and draw a 4-inch high line.

Draw out from the bottom of the 4-inch line the distance that you want the stairs to stretch across the floor to scale. For example, if you want the bottom step to sit 6 feet from the edge of the porch or deck, draw a 6-inch horizontal line. Lay a ruler between the ends of each of these lines and trace a sloping line between them to form a triangle.

Place a protractor at the corner of the triangle that you made where the top of the first line that you drew meets the sloping line and measure the angle. Check your local building codes to make sure that you have an angle that meets code before beginning to build the stairs. If the angle is too steep, you must extend the horizontal line to reduce the slope.

Measure the sloped line on the drawing once you have the proper angle. Change this measurement into an actual number to determine the length of the staircase. If the sloped line measures 5 inches, for instance, the actual staircase measures 5 feet. Cut two 2-by-12 boards to this length.

Divide the original height measurement that you took of the porch or deck floor to the ground by the desired height for each stair, such as 7 inches, the standard height. Round the number up to determine the number of steps in the staircase then divide the original height by the number of stairs to get the exact height of each step.

Slide a stair gauge onto one side of a carpenter's angle at the height you figured for each step. Slide another stair gauge onto the other side at the width that you want to make each step, such as a standard 12 inches.

Line the carpenter's square up on the first 2-by-12 board that you cut so the height stair gauge lines up at the end of the board and sits firmly against the edge. Let the angle drop down until the width gauge sits against the edge as well. Mark the “V” on the board then keep sliding the angle down the board and making “V”s that touch on their edges.

Remove the marked “V”s from the first 2-by-12 board with a saw. Place the first board against the second 2-by-12 board and trace the pattern of the first board onto the second to ensure that they match exactly. Secure these boards with bolts to the porch or deck frame so that the top edges line up with the porch or deck floor and sit 3 to 4 feet apart.

Cut stair treads approximately 2 inches longer than the distance that you spaced the supports. Use 2-by-12 boards to make the treads and place one tread between the supports on each cut section. Center the boards so 1 inch hangs off each side of the supports then screw them to the supports below with at least two screws on each side.