Earth integration: bermed (earth against walls), underground (earth over roof), or cut-and-cover. Advantages: extreme thermal stability (55-58F year-round underground), storm/tornado protection, minimal maintenance exterior, soundproofing, fire resistance. Structural: reinforced concrete or masonry rated for soil lateral loads. Waterproofing: critical — bentonite, membrane, drainage board, French drain. Challenges: natural light (courtyards, light wells, clerestory), moisture control, code compliance, psychology. Cost: $200-$400/sf. Famous: Earthship Biotecture (Michael Reynolds).