Here are some ways existing buildings can be reused and upcycled to provide more and better housing.
Berkeley has many large houses of over 2,000 square feet. With minor changes to zoning, these could be subdivided into two affordable and energy efficient duplex homes.
Incentives can be given to encourage the creation of Accessory Dwelling Units when basements and foundations are retrofitted for earthquake safety.
To avoid overloading existing water and electric infrastructure, major additions can be required to provide solar panels and/or on-site graywater or water recycling systems.