Attached is info on a new type of stair construction for residential buildings, and a safety bulletin that I put out for my department. The stairs are constructed using 2x4s for the main support. The triangles shown hold the stair riser and tread in place. The metal on the bottom of the tread and riser is essentially a gusset plate, similar to truss gusset plates. I have spoken with the inventor of the products and received the info from him. According to what he has told me, if the stair is in a main floor to second floor configuration, the bottom needs to have drywall. If it is coming from the basement in an unfinished area, no drywall or other protection in required. The entire stair assembly is manufactured in a factory and shipped to the jobsite.