The stairs' stringers, located on the sides of the stairs, must be designed and cut with care, since they're the structural ...

The usual technique is to bolt it to the stair stringers (the frame). But it'll only be solid if the stringers are solid.

Here is a picture of the side of a staircase. It’s called a stair stringer. Calculate the area of the side of the stringer that is facing you. Look for repeated shapes in it. Rhys has 8 of these ...