TOP ROW: It all started with a 9'-deep by 6-1/2'-wide by 15'-long hole in the ground . . . which was then lined with 3"" of polystyrene insulation .., and covered with waterproof black plastic. SECOND ROW: Joseph Orr and his son Jason next put alternating layers of dirt (each of which was soaked thoroughly with water after it was shoveled into place) and loops of 3""heat exchanger plastic pipe into the excavation . . . and framed in the inlet/outlet ends (and the ends only) of the plastic loops with temporary forms so that concrete could be poured around them. LEFT: A 6"" X 10"" continuous concrete footing was also poured in place around the base of the Orrs' greenhouse . . . and, once a low cement-block wall had been laid on that footing, another 3"" of polystyrene insulation (the same as in the pit) was placed against the inside of the block wall. BELOW: After insulating the top of the hotmud bin with 6"" of foam insulation, more black plastic was then laid down to cover and isolate the area inside the low foundation . . . anal enough topsoil, horse manure, and compost were hauled in to fill the interior of the greenhouse level full to the top of the foundation wall. Construction of the actual greenhouse was then begun over this efficient heat storage bin.