Precast concrete building units and method of manufacture thereof

A freestanding unitary precast concrete, one-half room building unit having an inverted U-shaped cross-sectional configuration and comprising:

• a generally horizontally extending web having upper and lower surfaces and opposite longitudinal edges;
• and
• a pair of spaced, generally vertically extending flanges having bases;
• said flanges being integral with and depending from said lower surface of said web respectively adjacent said longitudinal edges;
• said base of one of said flanges being formed with a tongue and said base of the other of said flanges being formed with a groove, and said tongue of said one flange being relatively dimensioned and configured to complement and fit into said groove of said other flange of an identical other unit brought in flange-to-flange inverted position relative to said unit;
• said web being dimensioned, configured and adapted to serve as the ceiling or floor of a room of a building and said flanges being dimensioned, configured and adapted to serve as upper or lower halves of the room;
• and
• said web being formed adjacent said longitudinal edges with alternating tabs and voids, the positions of said tabs adjacent one longitudinal edge corresponding to the positions of said voids adjacent the other longitudinal edge, and said tabs of said one edge being relatively dimensioned and configured to complement and fit into said voids of said other edge of an identical other unit brought in diagonally adjacent inverted position relative to said unit.