What to Clarify Before You Build an ADU in San Diego

An accessory dwelling unit can serve very different goals — rental income, housing for family, or added resale value — and the right design, budget, and process depend on which goal actually applies. This guide is a framework for the planning questions worth answering early; it does not offer zoning determinations, cost estimates, or return projections.

Published 2026-08-26.

Start with the goal, not the floor plan

An ADU designed for rental income can look very different from one designed for an aging parent or a future buyer. Naming the goal first keeps every later decision aligned with it.

  • Decide whether the ADU is primarily for rental income, family housing, or long-term property value
  • Consider how the goal affects size, layout, and finish-level decisions
  • Revisit the goal if your plans for the property change during design

Verify zoning, permitting, and lot-specific rules directly

ADU rules can depend on lot size, zoning, and existing structures. A neighboring property's example is a starting point for curiosity, not a substitute for your own verification.

  • Confirm current ADU regulations for your specific lot with the City of San Diego rather than a neighboring property's example
  • Ask about utility connections, setbacks, and parking requirements that may apply to your address
  • Work with a licensed designer or architect familiar with current ADU permitting requirements

Budget for the full project, not just construction

Design fees, permitting, utility connections, and a contingency reserve are as much a part of the budget as the construction line items.

  • Build a budget that includes design, permitting, utility connections, and a contingency reserve, not construction alone
  • Get contractor input on realistic timelines before committing to a schedule
  • Revisit the budget with your contractor if the scope changes during permitting or construction

Plan financing and the long-term operating picture separately

How you pay to build the ADU and how it performs afterward are two different questions, each best answered by the professional qualified to answer it.

  • Discuss financing options — cash-out refinance, construction loan, or other structures — with a qualified lender
  • If renting the unit, treat any rental income estimate as a planning assumption to verify, not a guarantee
  • Review tax and insurance implications of adding a second unit with the appropriate professionals

Related guidance

Schedule a consultation with Leon Cook

Common questions

Do I need a permit to build an ADU in San Diego?

Yes, ADUs require permitting. Requirements and allowances can vary by lot, so confirm the current rules for your specific property with the City of San Diego or a licensed professional.

Can I guarantee rental income from an ADU?

No. Rental demand and achievable rent depend on the unit, location, and market conditions at the time. Treat any income estimate as an assumption to test, not a guaranteed return.

Does an ADU always increase resale value?

Not necessarily in every situation. Impact on resale value depends on the property, the ADU's quality and use, and buyer demand in your specific area at the time of sale.