Build Stairs: Calculators in Order

Stairs are unforgiving because your legs learn the rhythm of the first step and expect it on every step after. The code limits the difference between the tallest and shortest riser to 3/8 in, so the work is to divide the total rise into equal steps and cut every one the same.

Everything starts with the total rise, measured from finished floor to finished floor. Divide by a target riser height of about 7.5 in and round to a whole number of risers: a 105 in rise gives 14 risers of exactly 7.5 in. The code caps risers at 7 3/4 in and requires treads of at least 10 in, and a 14-riser stair has 13 treads, so the run is 130 in at 10 in per tread. The run has to fit the floor plan, and if it does not, a landing turns the stair instead of cutting the tread.

Stringers carry the load, so their length, the depth of the cut and the remaining throat matter as much as the layout. Headroom of at least 6 ft 8 in over the stair, a width of at least 36 in and a handrail between 34 and 38 in high are the other numbers the inspector measures. Guards are needed where the drop is more than 30 in.

After the frame come the parts you see: tread boards, an optional runner, and balusters spaced so a 4 in sphere cannot pass. Plan the framing first and the finish second, and save each list to your project list.