How to Build an Interior Basement Wood Staircase

Measure the total rise of the area, from the opening of what will be the top of the stairs to the floor. Many basements are 9 feet in depth, so this measurement would be approximately 108 inches.

Divide the total rise by 7.5. This is the average rise of each step. For example, 108 divided by 7.5 equals 14.4, or rounded to 14. This is the number of steps you will need.

Find the complete run area of the stairs. Multiply the number of stairs by 10. Ten is the width or footing for each stair. For example, with 14 stairs, the complete run will be 140 inches. With this number, measure at an angle from the top to the floor. This is where the stairs will land or end.

Create the stringers. Set a 2-by-12-by-20 inch board on a hard flat surface and lay out the design for the stairs. Set a carpenter's framing square at one end of the board with one side of the square at 7-1/2 inches and the other side at the 10-inch mark. You will see how this will form the first step on the board. Trace around the square with chalk or a carpenter's pencil. Move the framing square down to meet the end of the first mark and create another step. Repeat for the number of steps needed.

Cut out the steps on the stringer with a circular saw. Follow the drawn lines carefully. Cut off the unused area of the board with a 45-degree cut from the bottom of the last step.

Lay the first cutout stringer on a second 2-by-12-by-20 inch board and cut a second riser. Use the first riser as your pattern.

Add additional support to the stringers with 2-by-4 inch boards. For a long staircase, it is advisable to add additional support for the stringers. Nail 2-by-4 boards to the lower, straight edge of each stringer for the entire run. Nail them in place with 3-inch nails every 8 inches.

Attach the stringers to the wall at the base of the door. Use an L-bracket on each side of the stringers to attach it to the wall just under the footer for the door frame. Drill the screws in place. Space the stringers no more than 4 feet apart.

Cut the boards for the steps. Cut one 2-by-6 inch and one 2-by-4 inch board for each step with the circular saw.

Attach the steps to the stringers. Lay a cut 2-by-4 inch board on the interior of the step area and nail it in place with 3-inch nails. Place a cut 2-by-6 inch board flush on the outer portion of the step and nail it in place. Repeat this process for each step.

Create the riser covers. Cut a piece of plywood to 5-1/2 inches by the width of the steps. For example, if your stairs are 3 feet wide, cut the pieces 5-1/2 inches wide by 3 feet long. Cut one piece for each step. Nail the plywood in place to cover the back of the riser.