Phototropic House is a site-responsive prototype for affordable housing in New Haven. It responds to solar conditions on-site, providing direct sunlight and solar heating to spaces at the time they are occupied. Phototropic House also provides an economy of construction, through a clear and straightforward hierarchy of formal and material elements. A series of operations generate the prototype depending on its specific location and orientation. The house begins with a square foundation, then close-packs program within a cubic envelope. Next is a tropic response; cantilevers are pulled over the foundation where light access is needed, resulting in a dense, central thermal column. Apertures are created by the shearing of the cantilevers, or are punched through the envelope to select views. Outdoor space is defined by the axes of these tropic cantilevers, within which private space is created using excess foundation soil.