For Aislyn and Ali Benjamin, an ADU, a small secondary home on an existing lot, was the most practical way into homeownership. They live near Danville, California - a small city just over an hour east of San Francisco - where the median home sale price was $1.8 million in August, according to Realtor.com. Wanting to stay near their jobs and avoid long-term renting, they built a 1,200-square-foot unit in the backyard of Ali's parents' home in San Ramon, a city next to Danville.