Accessory Dwelling Unit (ADU) Rules

A secondary living unit on the same lot as a primary home, such as a garage conversion, basement apartment or detached backyard cottage.

What typically applies

These are patterns seen across many US jurisdictions. They are not the rule at your address, because zoning is adopted locally.

• Many states now require cities to ministerially approve ADUs up to a set size, often around 800 square feet or a percentage of the primary home.
• Common local limits cover maximum floor area, height, rear and side setbacks, and lot coverage.
• Owner-occupancy requirements have been removed or limited by statute in several states.
• Parking requirements are frequently waived near transit or when converting an existing structure.

What most often changes the answer locally

• Whether the unit is attached, detached, or a conversion of existing space.
• Lot size, existing lot coverage and available setbacks.
• Sewer or septic capacity and utility connection requirements.
• Whether the parcel is in a historic district, coastal zone or wildfire interface area.
• Whether the local agency has adopted its own ADU ordinance with stricter objective standards.

Get a checklist for your address

Run the numbers for this project

Questions to ask your local department

1. Ask the local planning or building department whether a state ADU statute applies to your parcel and whether the city has a conforming local ordinance.
2. Request the objective standards used for ministerial review: size cap, height, setbacks and lot coverage.
3. Confirm utility connection requirements and any separate metering rules.
4. Ask whether owner occupancy, short-term rental use, or parking is regulated for your unit type.

See all project types on the yard rules hub, or use the yard rules checker for a different project. Planning more than one thing at once? The multi-project checklist builder merges them into a single printable list.

No statewide rule for your state? Yard permits are decided locally — the state government contacts directory links your official state portal and the local building department that sets the rule for your address.

ZoneFig provides general reference information, not legal advice. Yard and zoning rules are adopted locally, so the only binding answer for your address comes from your city, town or county planning and building department. Typical thresholds shown here describe patterns across many jurisdictions and are not the rule at any specific property.