The temperature of the ground at shallow depths corresponds to the mean annual air temperature (MAAT). If the MAAT in your location is 15.5C/60F, that's the te

The temperature of the ground at shallow depths corresponds to the mean annual air temperature (MAAT). If the MAAT in your location is 15.5C/60F, that's the temperature of your underground house. If you let in warm, damp air, it will condense inside. If there are any flaws in the drainage or waterproofing, it will get wet inside. If 15.5C is a little cool for you, you can insulate and install hardware to control the temperature and humidity. At this point, you've decoupled the internal environment from the surrounding environment. You're not 100% underground, so you're still not 100% protected from tornados or fire or bullets or COVID-22 zombies. Underground houses don't seem like a good solution for most situations. Passive House for the win!