Permit briefing
Do you need a permit for an ADU?
An ADU always needs a permit: it is a dwelling, with a kitchen and bathroom no exemption covers. What varies is its size, height and setbacks.
The reliable short answer
Start with the lot, not the floor plan: its zoning and size decide whether an ADU is allowed at all, and the size, height and setback lines decide what fits on it.
Planning complexity
High
Local answer required
Yes
The model code’s answer
Do I need a permit for an ADU?
Yes, always. The International Residential Code calls a unit with permanent provisions for living, sleeping, eating, cooking and sanitation a dwelling unit, which is what an accessory dwelling unit is, and its list of work exempt from a permit has no line for one. The plumbing, electrical and gas systems its kitchen and bathroom need take permits too: the exempt list covers repairs, some replacements, low-voltage work and portable appliances, not new systems.
| Rule | What it exempts |
|---|---|
| Model code (IRC R105.2) | None: a new dwelling unit takes a permit |
| Austin | None; new construction on SF-1 to SF-3 lots of 5,750 sq ft or more |
| Los Angeles | None; a complete application decided within 60 days |
Both checked cities take the permit as given and differ on what they allow. California's law makes an ADU a ministerial approval, decided within 60 days of a complete application: a city must allow one of at least 800 square feet and 16 feet, and may not require side or rear setbacks over 4 feet for a new unit. Los Angeles's ordinance repeats those lines and caps a detached ADU at 1,200 square feet and two stories. Austin, since its HOME amendments, allows up to three units on SF-1, SF-2 and SF-3 lots of at least 5,750 square feet, each permitted as new construction.
A three-step permit decision
1. Check that the lot qualifies
Austin allows an additional unit on a lot zoned SF-1, SF-2 or SF-3 of at least 5,750 square feet, up to three units in all. California allows one on any lot zoned for single-family or multifamily homes with a house on it or planned, and Los Angeles limits them on lots that are both in a Very High Fire Hazard Severity Zone and a Hillside Area.
2. Fit it to the size and setback lines
California caps a detached ADU at 1,200 square feet and an attached one at half of an existing house, yet no city may set a cap below 850 square feet, or 1,000 with more than one bedroom. Every city must allow 800 square feet at 16 feet high, with side and rear setbacks of no more than 4 feet. In central Austin, each new unit is capped at 40 percent of the lot's area or 2,300 square feet, whichever is greater.
3. Count the clock and the fees
A California city has 15 business days to say whether an application is complete and 60 days to approve or deny it, after which it is deemed approved, and no impact fee applies to an ADU of 750 square feet or less. Austin reviews an ADU as new construction, and an active permit expires on its 181st day if no inspection has been scheduled or passed.
What Austin and Los Angeles say about an ADU
Austin
- Permit
- Always. An additional dwelling unit is permitted as new construction, after it gets an address of its own, on a lot zoned SF-1, SF-2 or SF-3 of at least 5,750 square feet; since the HOME amendments such a lot may hold up to three units. The residential code's fire separation table applies.
- Fees
- Plan review for new construction is charged by square footage, on the city's fee schedule.
Los Angeles
- Permit
- Always, though without a hearing: the city must act on a complete application within 60 days. Its ordinance allows a detached ADU of up to 1,200 square feet and two stories, generally not between the house and the front street, and an attached one of up to half the house, with side and rear setbacks of no more than 4 feet for a new unit. On a lot in both a Very High Fire Hazard Severity Zone and a Hillside Area, it allows one only with sprinklers, a parking space and a 20-foot roadway, outside two community plan areas.
- Fees
- LADBS sets the permit fee from the project's valuation, and state law bars impact fees on an ADU of 750 square feet or less.
What to have ready before you call
- Zoning district and lot area
- Floor area, bedroom count and height of the unit
- Distance to the side and rear lot lines, and to the house
- Walking distance to the nearest public transit stop
- Water, sewer and electric connections, or a septic system
- An address for the unit, where the city wants a new one