California SB 9, signed into law in 2022, allows most single-family homeowners in San Diego to split their lot or add a duplex unit, opening up ADU possibilities beyond the standard accessory dwelling unit rules already in place. San Diego also has its own ADU-friendly local ordinances that in many cases allow attached or detached ADUs up to 1,200 square feet on qualifying parcels. Setback requirements, owner-occupancy rules, and utility connection fees all depend on your specific parcel, so a pre-application meeting with the City's Development Services Department, alongside advice from a licensed contractor familiar with local ADU projects, is the right starting point.