I made $20,000 in 5 months by renting out extra apartments in my Sacramento backyard

• George Warren added two ADUs to a duplex property he bought in 2004, aiming to earn extra income.
• In December, he started renting them for $2,000 a month each and has already earned $20,000.
• The ADUs have been so successful he plans on building more on another plot of land he owns.

This as-told-to essay is based on a conversation with George Warren, a 67-year-old adjunct journalism professor and real estate investor, who built two accessory dwelling units (ADUs) on his land. The essay has been edited for length and clarity.

My wife and I live in a century-old home in Sacramento, but also own 13 investment properties spread throughout Texas and California.