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Can I build an ADU on my property?

By the HyreADU research desk. Last checked .

The short answer

You can probably build an ADU on your property if it is in a residential or mixed-use zone and has a house on it or planned; California requires cities to approve qualifying ADUs ministerially.

What usually decides it is the specific lot: space after setbacks, the sewer or septic, fire and flood zones, coastal rules, easements and, outside California, the HOA. Only your city can confirm.

The questions that decide it

  1. Zoning: is the lot residential or mixed-use, with an existing or proposed home? (Gov. Code § 66323(a))
  2. Space: how much area is left after setbacks, easements and trees?
  3. Sewer or septic: can the line or system serve a second unit? See our septic research.
  4. Utilities: is there room on the electrical service? See our electrical research.
  5. Fire: is the lot in a high fire hazard zone with extra rules? See our fire code research.
  6. Coast: is it in the coastal zone, which adds a coastal permit in California (Gov. Code § 66329)?
  7. Flood: is it in a mapped flood zone? See our flood research.
  8. HOA or deed restrictions: what do they say?

What California law guarantees

California requires cities to approve ADU permits ministerially, without a hearing (Gov. Code § 66317), and to approve certain ADUs by right, including one detached ADU with four-foot side and rear setbacks on a single-family lot (§ 66323(a)).

A city cannot require you to fix nonconforming conditions on the lot as a condition of approval. It also cannot require owner occupancy for a full ADU (§ 66315).

Outside California

Several states, including Washington, Oregon, Montana, Arizona, Colorado and Maine, now require cities to allow ADUs in some form. Rules vary widely; see our ADU laws by state research and the locations hub.

Getting a written answer

The answer that counts is your city’s. Ask the planning counter for a pre-application meeting or a written zoning check, and bring a simple site sketch. The ADU feasibility checker prepares the questions. Our legalisation index and ordinance tracker show how local rules differ.

If the answer is no

If the city says no, ask for the reason in writing and the code section it relies on. Some blockers can be designed around; others, like a septic system that cannot be expanded, may end the project. Read ADU permit denied for the usual causes.

A mistake to avoid

The mistake to avoid is paying for full drawings before asking the city the questions above. A short pre-application meeting costs far less than a redesign.

What to do next: check your lot with the ADU feasibility checker, read the questions to ask an ADU builder, then tell us about your project. Matching is not live yet, so we reply with information, not a quote.

Get ADU options

Questions

Can I build an ADU if I rent my house?

Usually only the owner can apply for a permit. Ask your landlord.

Can my HOA stop me building an ADU?

It depends on the state. That page is held for legal review; our research covers the states we checked.

Do I need to live on the property?

Not for a full ADU in California. Other states vary.

Can I build an ADU on a vacant lot?

California allows an ADU with a proposed single-family home, built together. Ask your city.

Sources

HyreADU is a publisher. It does not design, permit or build ADUs, has no partner builders, and gives no legal, tax, lending or engineering advice.

Rules vary by state and city; California rules are labeled as such. Spotted an error? Tell us through our corrections page. Licensed professionals can also contribute as named sources.