Wall and floor structures of a building each comprise a base layer comprising prefabricated panels with grooved inner faces and a covering layer disposed over the panels to cooperate with walls of the grooves to define channels extending along the panels. Selected grooves contain in-floor heating elements and electrical wiring and routing components. A prefabricated corner panel is formed by notching out an oversized channel in the same type of panel, bending the panel along the channel and filling a remaining gap at the so-formed corner bend with a higher r-value insulation than the rest of the panel. Wall and floor panels are joined by a connector having a C-shaped portion that caps exterior floor panel edges and an integral projecting portion inserted into a slot formed in the wall panel's insulating layer at a bottom edge of the floor panel.