An earth-bermed house can reap about 95 percent of the energy advantages of a fully underground home, and adding an earth roof, or living roof, further promotes planetary health by "greening" the house's footprint.
You don't have to place an earth roof on an earth-sheltered home, but it has some compelling advantages in addition to the ecological benefit already mentioned:
The properly designed earth roof is the longest-lasting roof you can build, because the earth and insulation protect the waterproofing membrane from the three conditions that eventually break down every other common roof surface: ultraviolet radiation, erosion and freeze-thaw cycling, which all damage exposed roofing over time.
In winter, the cold, uneven earth roof holds snow better than other roofs, and fluffy snow is a good--and free--insulator.
Fully bermed sidewalls that meet the earth roof also add protection against earthquakes, tornadoes and hurricanes.
The earth roof is hands-down the most beautiful roof you can build, particularly one planted with wildflowers or several different sedum varieties.
Our south side is not earth sheltered at all, to take advantage of solar gain and to maximize fight; but the earth berm on the north of the two-story home is 13'deep, so we have an average of 6' of earth sheltering around the home, plus an 8"-deep earth roof. Fuel savings are compounded.
This frame is necessary to create internal spans short enough to support the heavy earth roof. The floor plan makes use of these beams, too.
The architect-stamped Earthwood plans are engineered to support the 150 pounds per square foot load of a snow-laden and saturated 8" earth roof.