More heat is lost from the one-story house due to its greater surface area.
Work Step by Step
A cube shape is compact and resembles a sphere, which has minimal surface area for the volume it encloses. Another way to think about it is that in a 2-story cube (architecturally known as a 4-square), more of the rooms share a wall or floor or ceiling with another warm room than with the cold outdoors. This is discussed on page 236, Figure 12.16.