Reading these comments makes me lose faith in humanity. Have any of you seen or felt 1/2" or 3/8" steel plate? Let alone 3/4" steel plate. Steel at that thickness could hold any human weight distributed anywhere on the plane of the stair. The anchor system would just have to be a metal beam in the wall where the stairs can be welded on. Seriously people. Just because you're not smart enough to understand it doesn't mean it's impossible!!

Manel and Anna, if this truly is your house...congratulations...it's gorgeous!!