How to Build a Post-to-Post Staircase System

Doing the Math

• First you need to figure the rise and run of your stringers, the vertical supports that suspend the stair treads in place and provide the angled ascent to the floor above. They are usually two-by-twelve boards attached at the stair angle, with the rise and run dimensions cut out for each step. A basic range of rise versus run ratio is acceptable by code and is derived from the natural step of the average person. The basic premise is to shoot for a rise of 7 inches and a run of 11 inches. Taking the overall height you need for the staircase versus the overall horizontal run you have available, you must divide to figure out how many steps you need to get close enough to this ratio to remain within code before cutting your stringers.

  For example, if you measure 8 feet from the floor to the upstairs landing, you first convert 8 feet into inches: 96. Divide that number by the average rise of 7 inches: 96 / 7 = 13.7 steps. Now work this backwards with a whole number of steps to fine-tune your true rise per step. Round to 14 steps: 96 / 14 = 6.86 inches per step. At 14 steps and an estimated 11-inch run, you need 154 inches of horizontal clearance, not counting the landing, to complete this staircase.

Setting the Stringers and Adding Treads

• Attach the stringers to the joist system at the top of the run with the appropriate hardware and hangers, allowing for finish details, such as drywall thickness beneath the outside edge of the stairs. Using a level, be sure they are all level from front to back and even with each other -- there are at least two stringers, often three for wider staircases. Attach the stair treads to the top of each step in the stringers, using hand-driven finish nails and a nail punch with a bead of wood glue on each stringer to prevent creaking. Cut your treads to allow for the thickness of the risers, plus any cove molding you wish to add, but keep them to a minimum to prevent tripping.

Building Newel Posts and Adding a Handrail

• Once the posts have been chosen, you must attach them to your stair framing so they can support the weight of a person falling into the railing. Fitting the stair tread around each post and adding a substantial base molding around the bottom of the post helps root them securely. Attach your handrail to both posts at an elevation of between 34 and 38 inches from the nosing of the treads to the top edge of the handrail, depending on local code, as this is the shortest point on the staircase from top to bottom. The handrail will terminate right into the vertical face of both posts unless an over-the-post design is chosen, which can be more complex.

Finishing the Balustrade

• The finishing touch, and possibly the most thoroughly checked by inspectors, is the placement of balusters along the staircase. Always check your local code for any deviations, but the most widely accepted rule is the 4-inch rule. All balusters must be placed with no more than 4 inches of space between any two to keep a small child from getting his head stuck. This presents an aesthetic choice for staircases more than mezzanines or decks because there is a series of treads to account for rather than a long run to divide these gaps across. Each tread can usually hold two balusters fairly evenly with this code constraint, and if the minimum is reduced a little further, they can be spaced quite evenly. Another solution is to group balusters into uneven, but patterned sets.