Can I Build an ADU? Rules, Permits, and a Parcel-First Checklist

The short answer

You may be able to build an accessory dwelling unit, but the answer depends on the parcel and the local rules—not just the city name. Start by confirming the zoning authority, whether ADUs are allowed in the district, and whether the lot has enough usable area after setbacks and other constraints.

What counts as an ADU?

An accessory dwelling unit is a smaller independent home on the same property as a primary residence. It can be detached, attached to the house, created inside the house, or converted from an existing garage. Local codes may use another name, such as accessory apartment, coach house, backyard cottage, or secondary dwelling.

The five questions that decide feasibility

1. Is an ADU allowed in the zoning district, and is it permitted by right or through a special review?
2. Does the parcel satisfy minimum lot size, frontage, coverage, open-space, and setback rules?
3. Do height, floor-area, bedroom, parking, owner-occupancy, or design limits apply?
4. Can water, sewer or septic, electrical, fire separation, and emergency access requirements be met?
5. Are shoreland, floodplain, historic-district, airport, easement, or homeowners-association constraints present?

Start with the parcel, not a generic city rule

Citywide ADU guidance is useful, but a parcel can sit in a special overlay or have a shape that makes a nominally allowed ADU impractical. Confirm the official parcel boundary and zoning authority, then map the required yards and any existing structures. Do not use a geocoder-made square or an approximate tax-map image as a surveyed boundary.

Common permits and reviews

Most ADU projects involve a zoning or land-use review and a building permit. Electrical, plumbing, mechanical, driveway, utility, erosion-control, or sanitary permits may be separate. A conversion can also trigger change-of-use, fire-separation, egress, energy-code, or structural review even when the exterior footprint does not change.

A practical order of operations

1. Verify the parcel, municipality, and zoning district.
2. Confirm that the ADU type is allowed and identify every discretionary review.
3. Draw a preliminary footprint inside the buildable area.
4. Check utilities, access, parking, and existing structure conflicts.
5. Ask the reviewing office to confirm the current forms, fees, and submittal sequence.
6. Only then invest in permit-ready drawings or construction pricing.

What information should you gather?

• Property address and parcel number
• A boundary survey when dimensions or placement are close to a limit
• Existing building locations and uses
• Proposed ADU type, footprint, height, bedrooms, and access
• Water, sewer or septic information
• Easements, recorded restrictions, and association rules

FAQ

Can I build an ADU if my city generally allows them?

Not necessarily. The district, lot size, setbacks, coverage, overlays, utilities, and project design still control the parcel-level answer.

Do I need a survey?

A survey is often prudent when the proposed footprint is close to a setback, easement, shoreland line, or other boundary. Public GIS is useful for screening but is not survey-grade.

Can I convert an existing garage?

Sometimes. The conversion must satisfy local ADU rules and building-code requirements such as structure, insulation, egress, fire separation, utilities, and legal access.

Does an ADU always require a building permit?

New construction and most conversions generally require permits. The exact permit set and filing authority vary by jurisdiction and scope.

Use GovCodex Permit Check with the property address and your exact project description to turn this checklist into a parcel-specific starting point.