A homeowner with 8,000 square feet of lot and an unfinished basement-or-yard faces a version of the same question: "should I do an ADU or an addition?" From a livable-square-feet standpoint, the two options can land in roughly the same place. From a permit standpoint, they can follow quite different paths.
The case for an ADU
- Several states, including California, Arizona and Washington, limit how restrictive cities can be on ADUs. California also sets a deadline: the city must approve or deny a complete ADU application within 60 days when there's an existing home on the lot.
- Some cities offer pre-approved ADU plans; using one can shorten design and review. Check whether your city has a program.
- In states with ADU laws, setback and parking rules for ADUs are often more permissive than for an addition. Arizona's 2024 law, for example, bars cities over 75,000 from requiring extra ADU parking or side and rear setbacks over five feet.
- Separate utility meters are possible; whether they need a service upgrade depends on the existing service and the utility.
- Rental income or family-occupancy options open up that an addition does not provide.
The case for an addition
- You connect into existing HVAC, plumbing, and electrical, which can be cheaper than running new utility services.
- Additions need a standard residential permit; HOA design review, where it exists, can apply to either path.
- You keep the property as a single-unit residence, which simplifies refinancing, insurance, and resale.
- Aesthetic continuity is easier — match the existing roof line, windows, and exterior materials.
Where the ADU path can be more predictable
In California, the 60-day decision deadline and state limits on what cities can require often make the ADU path the more predictable one. Elsewhere, ADU laws may limit what cities can require without setting a review deadline, so check the city's published review times. Both ADUs and additions still go through building-code plan check.
Where additions can be faster
Small additions may qualify for a city's express or over-the-counter review, where the city offers one. And in jurisdictions where the ADU statute has not been adopted (or where the city is still arguing about implementation), the addition path is sometimes the predictable choice. Texas, for example, has no statewide ADU law; each city sets its own ADU rules.
Rule of thumb: in a state with an ADU review deadline, like California, check the ADU path first. Where there's no state ADU law, compare the city's ADU and addition rules before choosing.
What we tell clients
On the kickoff call, we pull the parcel, check the local ADU rule against the state statute, and tell you which path looks more predictable on your lot. California's 60-day decision deadline favors the ADU path; in Texas, with no statewide ADU law, it depends on the city. Other states (Nevada, Ohio) depend on the AHJ.
If you are weighing the two and the timeline matters, send us the parcel APN and the city. We reply within one business day.