At Mixed House Design interior apparently, the staircase had not been built on site and was designed without a center support or stringer. Residence built with mixed structure: glued laminated eucalyptus in the center, reinforced concrete on the perimeter. All about Staircase interior design, This Staircase would have to make climbing steps a lot more fun. Mixed House Design Designer: Vazio S/A Arquitetura e Urbanismo, Location: Brazil, South America. The two structures are mixed and create a certain excess of pilars througout the house.