ADUs · Checklist · Reviewed July 14, 2026
ADU first-stop check
What to check before a garage, backyard, or spare room becomes a small second home.
The short version
Pick the unit type before reading the local checklist
The unit type comes first. A full ADU is a home of its own, with room to live, sleep, cook, and use a bathroom. A JADU is no more than 500 square feet; it sits inside a single-family home and can use an attached garage. California gives both types a faster review path when the plans follow set rules, but both still need permits and a certificate of occupancy.
What changes the answer: An 800-square-foot ADU has a strong state-law lane, but 800 square feet is not the maximum everywhere. Unit type, bedrooms, existing space, utilities, coast, septic, and fire conditions can change the path.
State law gives ADUs a strong lane. The address still decides the office, fees, water, sewer, coast, septic, and fire checks.
How it works
ADU, conversion, and JADU mean different plans
A detached ADU is a separate backyard building. An attached ADU adds space to the main home. A conversion ADU uses existing house, garage, or accessory-building space. A JADU stays within a proposed or existing single-family home and may share its bathroom with the main home.
A JADU cannot exceed 500 square feet. Only one JADU fits a single-family lot. If it shares sanitation with the main home, an owner generally must live in the JADU or the main home. A normal ADU generally cannot carry a local owner-occupancy rule.
The protected size numbers do different jobs
A local ordinance must allow a maximum of at least 850 square feet, or 1,000 square feet when the ADU has more than one bedroom. Separate state rules keep lot coverage, floor-area limits, and open-space rules from blocking at least an 800-square-foot ADU with four-foot side and rear setbacks.
There is no state minimum lot size for an ADU. A city may allow more than the state floor, and some conversion units are not bound by the normal unit-size rules. Height, front setback, building separation, hillside, fire, and coastal standards still need the local sheet.
Parking can be one space or none
A city or county cannot ask for more than one parking space per ADU or one per bedroom, whichever is less. It cannot ask for guest parking. If a garage or carport becomes an ADU, the lost parking does not have to be replaced.
Some ADUs need no parking. This includes a unit within a half-mile walk of transit or one block of car share. It also includes a unit in a historic district or inside space that is already part of the home or another building. No space is due when the city does not offer parking permits to the ADU tenant. Some other state-law ADUs also have no parking rule.
The first written clock is 15 business days
The permit office usually has 15 business days after it gets the file to say if it is complete. The answer must be in writing. If the file is not complete, the notice must list what is missing and how to fix it. If the office misses that clock, state law treats the file as complete.
A complete file that fits the state path usually must be approved or denied within 60 days. A delay asked for by the owner stops that clock for a time. A denial or incomplete finding must have an appeal path. The final written appeal answer is usually due within 60 business days. No one can move in until the final certificate is issued.
Seven hundred fifty square feet changes impact fees
A local agency, special district, or water corporation cannot impose impact fees on an ADU with 750 square feet or less. Above 750, the fee must be proportional to the ADU's size compared with the primary home. A JADU of 500 square feet or less is also exempt from those impact fees.
School fees use a different line and may apply to an ADU over 500 square feet. Plan-check, building, utility, and other service charges are not all impact fees. A conversion and a new detached unit can also receive different water or sewer treatment, so ask for an itemized fee sheet.
State protection does not erase site limits
Adding an ADU cannot by itself force sprinklers into an older main home. The ADU or JADU usually needs sprinklers only when the main home needs them. A new detached ADU may also need solar under the Energy Code. Many garage and room conversions do not.
Site limits still matter. They can include septic, the coast, water, easements, utility space, and fire access. A local health officer must review an ADU on a septic lot. A local coastal plan can change the rules near the coast. Even there, a complete ADU permit file still has a 60-day decision clock.
First moves
- 1
Find the address, parcel number, and city or county.
- 2
Pick the kind of unit: backyard, garage, attached, inside the home, JADU, or a unit in an apartment building.
- 3
Open that city or county ADU page. Save the checklist, fee sheet, and plan list.
- 4
Keep HCD's ADU handbook nearby and compare local rules with the state ADU path.
- 5
Ask what makes the file complete.
- 6
Ask how the 15-business-day complete-file check works.
- 7
After the agency finds the application complete, ask how the 60-day approval-or-denial clock applies to the project.
- 8
If the agency denies the application, read the written reasons and ask about the state-law appeal path and its 60-business-day decision period.
- 9
Ask early about water, sewer, fire access, power, school fees, impact fees, and utility meters.
- 10
For a unit of 750 square feet or less, separate ordinary permit charges from impact fees and ask for each line in writing.
- 11
If the home has septic or sits near the coast, call that office first.
- 12
Before hiring, check the license and ask for a written permit plan.
Watch for
- 1
An ADU is not a no-permit job. It is a faster permit lane when the plans fit.
- 2
Local rules need to be clear and written. A vague taste test should not decide it.
- 3
For a qualifying ADU application, the agency generally has 15 business days to tell you whether the filing is complete and 60 days after a complete application to approve or deny it.
- 4
The state appeal path has its own rules and does not cover every local decision. Read the denial and current HCD guidance before relying on it.
- 5
If the office says no, ask for the written rule and the missing-item list.
- 6
Small ADUs and JADUs get fee limits. Other plan, utility, school, and permit costs can still show up.
- 7
A JADU with a shared bathroom generally carries owner occupancy. A normal ADU generally does not.
- 8
Coastal lots, old homes, fire areas, hillsides, easements, and septic can add work.
- 9
A cheap design or build quote is not the same thing as permit approval.
Official sources
Where to confirm this
Use the source that matches the step you are on. Current forms, fees, deadlines, and agency decisions can change after this page is reviewed.
Use this as a map. It does not decide your rights, tell you what to file, or say someone broke the law. If a deadline, denial, eviction, firing, injury, tax bill, permit fight, or insurance dispute is on the line, use the official source or a licensed professional.