Property-first ADU planning

Can I Build an ADU on My California Property?

Screen the property before paying for a floor plan. Identify the jurisdiction, rules, site constraints, utility questions and budget evidence that determine whether an ADU is worth pursuing.

California context updated: September 3, 2026Audience: California homeownersScope: Early planning—not a Title 24 compliance assessmentResult: A planning file—not a permit decision

On this page

California ADU planning toolkit · Start here

Find your next step before you design.

Five short steps turn your property facts into a preliminary pathway, questions for the agency and an evidence plan. “Not sure” is a useful answer.

Loading the planning steps. If they do not appear, use the property evidence checklist below.

The short answer

Start with three separate questions.

Legal

Is an ADU allowed here?

Identify the correct city or county, then verify the ADU pathway, allowed types, size, setbacks, height, parking and occupancy or rental rules.

Physical

Can the property support it?

Check existing structures, usable space, access, slope, drainage, trees, hazards, easements, utilities and emergency access.

Financial

Does the complete budget work?

Include design, permits, site work, utilities, construction, financing, contingency and the value of alternatives you give up.

A “yes” to zoning is not a complete feasibility answer. A project can be legally allowed but impractical because of access, utilities, hazards, site work or budget.

Verify rules in the right order

Separate state, local and property-specific requirements.

State baseline

Determine whether state law establishes minimum permissions, review timelines, fee rules or limits on local restrictions.

City or county rules

Confirm which jurisdiction issues the permit. Then read its current ADU standards and application instructions.

Property overlays and recorded constraints

Check hazards, historic districts, coastal or environmental areas, utility easements, covenants and other parcel-specific conditions.

Agency confirmation

Record the source, date and department. Ask focused written questions when official material is unclear.

What changes feasibility

Property facts to collect before design.

Topic Questions to answer Evidence to collect in California
Parcel and structures Where are the boundaries and existing buildings? Is prior work permitted? City/county GIS and assessor records as starting points; a survey when needed, measured site plan, and building-department permit history. For previously unpermitted ADU work, record construction-date evidence and review the current legalization protections before asking the agency about its process.
Access Can people, equipment and emergency responders reach the proposed area? Site measurements, fire guidance and contractor walk-through.
Sewer or septic Where is the connection? Is gravity drainage possible? Does septic capacity exist? Sewer-provider maps, connection records and a sewer scope where needed; septic permits, system capacity records and written requirements from the responsible local environmental-health agency.
Electrical and water Is existing capacity adequate? Are separate meters required or desirable? Panel and service specifications, an electrical load assessment by a qualified professional, water service/meter information and written utility requirements. Ask the designer or building department which California energy-code requirements apply to this project.
Slope, drainage and soil Will excavation, retaining, stormwater or geotechnical work be needed? Topographic information, drainage review and professional assessment.
Trees and hazards Do protected trees, wildfire, flood, coastal or other overlays affect the site? Official maps and specialist review where warranted.

What to do next

Move forward without paying for the wrong work.

Create a one-page property brief

Record the address, jurisdiction, household goal, desired ADU type, rough size, existing structures and known constraints.

Confirm the planning pathway

Use official sources and targeted questions. Save links, written answers and review dates in the project file.

Build an evidence-based budget

Use local allowances for construction, professional services, government fees, site work and utilities.

Engage design help at the appropriate level

Once the basic pathway is plausible, choose the professional needed to test layout, code and site assumptions.

Check California ADU Laws →Open the ADU Budget Calculator →Compare ADU Types →Compare JADU vs ADU Requirements →

Dynamic feasibility screening tool

Build your California ADU evidence file

Open each item to see the California rule, what to investigate, and what evidence belongs in your file. Check an item only after collecting that evidence. This is an early screening record—not a permit decision. Nothing you type or check is submitted to us.

1. Correct jurisdiction identified

Confirm who controls land use and permits.
The California ruleA postal city name does not always identify the permitting authority. A parcel may be inside a city or in an unincorporated county area. Fire, water, sewer, septic, coastal, and environmental review may involve additional agencies.
What to look forOpen the city or county parcel map. Match the parcel number and property location. Check whether the map identifies an incorporated city or unincorporated county area, then list every separate reviewing agency.
What counts as evidenceA saved or printed official parcel/GIS result identifying the parcel and jurisdiction, plus written planning or building confirmation when the boundary is unclear. Record the parcel number, source, and date checked.

A mailing address alone does not settle jurisdiction.

2. Current official ADU rules located

Collect the state baseline and current local instructions.
The California ruleCalifornia law establishes important minimum permissions and limits on local restrictions. Local objective standards, application instructions, and property-specific requirements still matter. An ordinance date alone does not prove that every provision reflects current state law.
What to look forFind the local ADU ordinance or standards, current application checklist, fee schedule, and department contact. Compare them with the current California HCD ADU Handbook and the state-law sections relevant to the proposed ADU pathway.
What counts as evidenceSaved copies or links for the current local standards and application materials, the current HCD handbook or statutes used for comparison, and a dated written agency answer for any conflict or unclear point.

Use official sources; a builder blog or search result is not rule evidence.

3. Property boundaries and setbacks confirmed

Measure from verified lot lines—not assumed fences.
The California ruleFor many new attached or detached ADUs, a local agency may require no more than four feet from side and rear lot lines. Specified ADUs created within an existing structure—or replacing one in the same location and dimensions—have different setback treatment. Front setbacks, building separation, safety rules, and overlays require separate review.
What to look forLocate every lot line, existing structure, proposed footprint, access path, and known easement. Determine the project pathway before applying a setback rule. Flag any dimension close enough that a small measuring error would affect the design.
What counts as evidenceA dimensioned site or plot plan tied to actual property lines, supported by a boundary survey when a line is uncertain or the project is close to a limit. Show structures, access, easements, and the proposed ADU.

Government Code §66314(d)(7). Do not measure from a fence unless its boundary location is verified.

4. Allowed size and height confirmed

Match the concept to the correct state and local pathway.
The California ruleState law protects the ability to create at least an 800-square-foot ADU with four-foot side and rear setbacks and a height of at least 16 feet, subject to the applicable statutory pathway and health and safety standards. Other state height rules may require more than 16 feet in specified situations. Larger units depend on project type and lawful local standards.
What to look forPlace the proposed width, length, floor area, stories, and height on the site concept. Check whether the design relies on the protected 800-square-foot envelope, a conversion pathway, a local allowance for a larger unit, or a state provision requiring additional height.
What counts as evidenceA dimensioned concept plus a written standards summary citing the applicable state pathway and local rules. For a unit over 800 square feet or a greater-height provision, keep written agency confirmation or a qualified designer’s documented code analysis.

The 800-square-foot and 16-foot standards are not an automatic permit or the only possible design.

5. Electrical service and energy path screened

Check capacity, routing, metering, and project-specific energy rules.
The California ruleAn ADU can increase electrical demand. California Energy Code treatment varies: a newly constructed detached ADU is generally treated as a new building, while attached ADUs and conversions of unconditioned space are treated as additions. Solar PV requirements therefore are not identical for every ADU.
What to look forRecord the service and panel ratings, major existing loads, proposed all-electric equipment, meter plan, possible trench route, and utility equipment location. Ask whether service, panel, transformer, or meter work is likely.
What counts as evidenceA written load calculation and panel/service recommendation from a qualified electrical professional, plus written serving-utility requirements when a service change, new meter, trenching, or transformer work may be needed. Retain applicable energy-compliance forms.

A panel photograph or amp rating alone does not prove available capacity.

6. Sewer or septic path confirmed

Separate physical capacity from fees and connection rules.
The California ruleImpact fees and utility connection charges are different questions. Requirements and charges can depend on the ADU category, existing dwelling, utility provider, and whether separate conveyance is proposed. Septic approval depends on the responsible local environmental-health agency and system capacity.
What to look forFor sewer, identify the lateral, route, elevation, condition, cleanouts, and provider. For septic, locate the tank and disposal area, review permitted capacity and bedroom count, and protect required reserve areas. Ask what documents the reviewing agency requires.
What counts as evidenceFor sewer: provider records and written confirmation of connection work and charges, with a lateral scope when condition or routing is uncertain. For septic: current system permits/records and written clearance or design requirements from environmental health.

Government Code §66311.5. The under-750-square-foot impact-fee rule is not a universal waiver of utility work or connection charges.

7. Hazards, overlays, and recorded constraints screened

Check the parcel against every relevant official layer.
The California ruleFire, flood, coastal, historic, environmental, fault, slope, protected-tree, drainage, and recorded-easement conditions can change design and review. Some state and local standards continue to apply even when an ADU pathway exists.
What to look forReview the official layers relevant to the parcel and note the map date. Read title or easement documents, not just a map symbol. Where a boundary crosses or approaches the property, ask the responsible agency which requirements are triggered.
What counts as evidenceA dated parcel screening file containing official map results, title/easement documents, and agency records. If a source flags the parcel or is unclear, add written agency guidance or the appropriate specialist report. Commercial reports should identify source layers and dates.

No flag found means only that the sources checked showed no flag; it does not prove that every concealed or unmapped condition is absent.

8. Complete first-pass budget prepared

Include every likely project cost—not only construction.
The California ruleA local agency generally may not impose an impact fee on an ADU with 750 square feet of interior livable space or less. This does not eliminate plan review, building permits, school fees where applicable, utility work, professional services, or construction costs. ADUs with more than 750 square feet of interior livable space are subject to state proportionality rules for impact fees.
What to look forPrice design, engineering, surveys, reports, agency and school fees, demolition, site work, utilities, construction by trade, finishes, appliances, financing, temporary impacts, landscaping, escalation, and contingency. Compare bids only after scopes match.
What counts as evidenceA dated, itemized estimate with each inclusion, exclusion, allowance, site assumption, and contingency shown separately. Support high-risk lines with agency/utility information or qualified trade estimates rather than a generic cost-per-square-foot figure.

Government Code §66311.5. Verify current local fee schedules and utility estimates.

Method and limitations

This is a screening framework, not an approval.

California source notes added September 3, 2026: §66314(d)(7), setbacks; §66311.5, impact fees and utility charges; California laws hub and code crosswalk. This update is not a parcel-specific or municipal compliance review.

The checklist measures whether important questions have supporting evidence. It does not interpret local law, inspect the property, identify concealed conditions or replace advice from the authority having jurisdiction and qualified professionals.

Important: California ADU requirements depend on the current law, local jurisdiction, project pathway and property conditions. Verify jurisdiction-specific requirements with current official sources before purchasing plans, signing contracts or making financial commitments.