Most of the pretending innovative modern housing projects show a common element that can be perceived when looking at the cross-section, evidencing the use of alternate corridors, which was recognized as a projective technique under Wells Coates expression “Planning in Section”. Contrasting virtues concerning the resulting space were observed at different historical moments. The late 19th Century used it to create privacy. The modern architecture used it to increase efficiency, where flexibility was included. However, during the ’60s, the alternative corridor technique started to be used to attend social issues, popularizing the split-level term, and echoing 19th Century privacy interests. Keywords like Smithson’s “doorstep” and Candilis “semi-duplex” section reveal their approaches. Well-differentiated areas (public/intimate/collective) and socially controlled areas were obtained in domestic interiors with a few steps, creating singular spaces where children can play while being monitored by adults. Semi-duplex geometry showed new adaptability to different profiles: a small kitchenless apartment for a bachelor could be inserted aside from a larger two-level family apartment. This paper shows an overview of this projective technique by contrasting different housing projects. Since similar split-level geometries seem to have been coming back recently, questions about it are necessary.