To build a set of stairs, calculate its rise and run, cut stringers according to the calculations and install them, then attach the treads and risers to the stringers. Building stairs is fairly straightforward, with just a few design choices that builders need to consider before starting.
First, decide on a width and step height for each stair. These factors influence the stairs' run, which is the horizontal distance it covers, and its rise, which is the change in vertical height it achieves. The ratio of rise to run affects the steepness of the stairs, which may be subject to the provisions of local building codes.
Next, use the figures for rise and run per step to calculate the stairs' total rise, run and number of steps. Divide the total measured rise of the stairs by the desired rise per step. This yields the total number of steps required. Multiply the number of steps by the desired run per step to obtain the stairs' total run.
Then, identify the correct length for the stringers. Using the distance obtained by calculating the total run of the stairs, find its starting point. Measure and cut several lengths of 2-by-12 inch wood long enough to span the diagonal distance from that starting point to the point the stringers meet the deck or upper floor. Cut even, leveled notches into stringers to hold the steps.
Finally, measure and cut boards to serve as risers and treads. For easy installation, attach the risers before installing the treads.