> no natural light > no easy way to air out your house > probably going to end up mold infested and humid if lacks good ventilation > digging and setting up a stable underground structure is way harder than building a covered plywood box you can start digging and see how it fares. honestly a lot of people are going to have to start pirate living once the economy collapses and the shantytowns come back. you could go dig an underground house right now and live somewhere without paying for the land or property taxes. you probably won't want to live like that permanently as you'll never get a girl to agree to raise kids like that.
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