Might I answer David's question?
David, can I answer your question?
You asked a question about an underground house. I myself have built several houses in the ground, and I can tell you that the cost is too high in relation to the energy savings. It must be said that when you take into account energy, it is the entire energy cycle that you must look at. The construction of such a house consumes too much energy compared to what it can give back.
However, such houses are built in areas where there are hurricanes and tornados, in the American Midwest and on islands that are hurricane-prone. In France, there are entire villages that are covered in earth.