Stringers

• Stringers provide the underlying support and become the element the stairs rest upon. For wood stairs, a 2-by-12-inch length of wood becomes the stringer. The stringer turned on end spans the distance from the ground floor to the top of the finished next floor. The top end of the stringer, cut at an angle, attaches to the floor above. Determine the angle of the stringer by calculating the rise and run of the stair. The bottom end of the stringer rests on the ground floor foundation. Make cuts into the stringer at a 90-degree angle spaced equally, which becomes the base for the stair tread rise and run.
  
  

Rise and Run

• Some local building codes use the International Building Code while others use the Uniform Building Code. In both cases, safety drives stair-building requirements, but local building codes delineate the minimum and maximum requirements for stairs. Each stair step must be equal in height, depth and nose to the stair before and after it for safety. The height or rise of the stair under UBC and IBC calls for a maximum stair height of between 7 3/4 and 8 1/4 inches. The nose of the stair or its maximum overhang is between 1 1/4 to 1 1/2 inches. Tread length or run is a maximum of between 9 and 10 inches. Verify local building codes for minimum and maximum requirements.
  
  

Width and Handrail

• Stairs must be a minimum of 36 inches wide under UBC with a wall-mounted handrail on either side. The handrail can only stick out into the staircase area 3 1/2 inches. For stairs not built inside walls, handrails must be at minimum 36 inches tall with not more than 4 inches between the spindles or balusters, approximately three balusters per tread.
  
  

Calculations

• To calculate how many steps the staircase will have, divide the total rise by the maximum riser height. The total rise is the distance from the ground floor to the top of the next finished floor. For the International Building Code, the maximum riser height is 7 3/4 inches. For a 9-foot height, take the 9 feet and multiply it by 12 inches; divide the result by 7 3/4 inches. Round the numbers up to achieve the final number of stair steps. This stringer run calls for 14 steps at a maximum height of 7 3/4 inches.
  
  

Stair Treads

• Stair treads are placed across the stringer using one, two or three boards, depending on the construction design. For interior use, stair treads generally call for one board as the stair tread while outside stairs use two or more boards. Board width is determined by tread run and nose overhang. Once stringers are cut and secured, stair treads are put in place one stair at a time. If desired and included in calculations for stair depth, facing may be added to the face of each stair tread for interior stairs.