How a house is built
The flight of stairs
The stair on this house links the two floors. Rise, run, headroom, and a guard are the teaching points, not a stair design.
Arrow keys turn the house. Plus and minus, or the zoom buttons, change the zoom. A horizontal drag turns it after you tap the drawing. Reset view returns to the step camera.
The drawing needs WebGL. The notes on the page still stand.
A stair is a floor folded so people can change level. The rise of each step and the run of each tread stay consistent, or the gait breaks. In the International Residential Code a common limit is a riser no taller than 7 3/4 inches and a tread at least 10 inches. Local amendments differ. A guard is required on the open side, and a handrail where the code asks for one. Headroom has to clear the walking line, including at the landing.
The flight on this house runs across the plan and arrives on the upper floor. The treads in the model are drawn so the stair reads. They are not a claim that this flight meets the code numbers. The opening in the upper floor is part of the framing, cut before that deck is finished.