A nice, warm spring day here in the Mohave Desert. This thermometer usually hits 125 degrees in the early afternoon starting in June. We have three feet of dirt on the roof. The back and sides are buried, leaving only the south face exposed. Our house is basically a 12-inch-thick concrete box, wrapped in styrofoam and buried in dirt. The roof has 6 inches of styrofoam and the sides have 3 inches. There is no R-value in either concrete or dirt, so the only insulation comes from the styrofoam. 6 inches X R4.7 = R28.2. I'm counting on the thermal mass of the concrete and dirt to even out temperatures. Instead of battling temperatures from 30F to 125F, the dirt around the shell of our house will be a nice, even 75 degrees(I'm guessing. I don't know for sure.)
We still haven't moved in and we have not turned on the heat pumps since they were installed and briefly tested in January. We now know that the sun will completely heat our home during the winter. We won't have to turn on the heat pump at all during the cold months. Summers here are a brutal test of a dwelling's energy efficiency. We'll closely watch the performance of our home. Stay tuned.