How to Build Stairs for a Sunken Room

Measure the total rise of the stairs, which is the total distance from the bottom of the staircase to the surface of the floor at the top of the staircase. Divide this number by 6 or 7 inches, the appropriate height for each stair riser. This will give you the number of stairs in your staircase. For example, if the floor of the sunken room is 21 inches below the level of the higher room, divide 21 inches by 7 inches to get the number of steps in the staircase, which in this case is 3. The riser height is 7.

Find the total run of the staircase, which is the horizontal distance of the staircase from the upper floor to the edge of the stairs at the bottom floor of the sunken room. Consult the building inspector to find out the required slope or incline prescribed by the building code. The slope of a staircase is typically 30 to 35 degrees. For a steeper incline, the total run is shorter; and for a shallow incline, the total run is longer.

Install stringers, the diagonal pieces that attach to each side of the stair treads, to the top of the stairs. Mark your calculations on the stringers and install the L-shaped brackets on the stringers. Install the stair tread boards so they rest on the brackets and screw in the treads. Use at least two screws for every tread so they will not come loose.

Apply the predetermined riser height to the 2-by-12-inch boards and cut them to size the same length as the stair treads. Cut one riser for each step, using the predetermined number of steps in the staircase. In our example, the riser height is 7 inches and the number of steps is 3. Attach the vertical stair risers to the stringers using wood screws so that the edges of each riser touch the side of the stringers.