ADU Planning Basics for Homeowners

Create a property-specific feasibility record

Identify the jurisdiction, parcel conditions, existing structures and intended ADU use. Collect a site plan or available records and ask the local planning and building departments what applies. State ADU law and local implementation are not static; use HCD's current handbook and agency guidance instead of assuming a rule from an older article still applies.

Ask about access, utilities, drainage, setbacks or other applicable site constraints through qualified professionals. A detached new structure, garage conversion and internal conversion can have different existing-condition questions. Do not price them as the same project simply because their floor areas match.

Build a full team and operating budget

Define design, engineering, permits, utility coordination, site work and construction responsibilities. Request a budget that includes connections, trenching, restoration and owner purchases. Clarify which costs remain estimates and what investigation could narrow them before the construction agreement.

For rental use, discuss management, insurance, utilities and applicable rental rules with appropriate advisers. For family use, consider accessibility and future flexibility. Project feasibility does not establish rental income or investment return. Have tax and financing questions reviewed separately rather than rolling them into a construction savings claim.

Start with feasibility

Property constraints, access, utilities, zoning and local requirements can shape what is practical. Verify current requirements with the appropriate local agencies and qualified professionals.

Define the intended use

Family use, rental use, accessibility and long-term flexibility can influence layout and systems decisions.

Map the full project team

Depending on the project, design, engineering, permitting, utilities and construction may involve multiple professionals. Understand responsibilities before assuming one quote covers everything.

A practical example

Illustrative scenario only. These figures and situations are not local price averages, quotes or promises of results.

An apparent garage conversion estimate excludes utility upgrades and work needed to address the existing structure. A feasibility review identifies those dependencies before final design. The early investigation may cost money, but it helps avoid comparing an incomplete conversion price with a complete detached-unit proposal.

Questions worth asking

Use these questions to test whether the explanation or proposal actually addresses your situation. Ask for a written answer when it changes the scope, price, responsibility or timeline. A confident sales presentation is not a substitute for a specific answer.

• Which jurisdiction and current rules apply?
• What utility and site work is excluded?
• Who coordinates design and approvals?
• What assumptions remain unresolved before contracting?

Compare the complete cost and the payment timing

Keep the project price separate from how it is paid. List the diagnostic visit, labor, equipment or materials, access work, restoration, disposal, approvals and any owner purchases. Write included, excluded or unknown beside each item. A missing cost is a question to resolve, not a zero to insert into the budget. If the same item appears in two quotes or invoices, check whether it would be counted twice.

Ask when deposits, progress payments and remaining amounts are due and what completed work or delivered material supports each milestone. Compare financing using its written terms rather than only a monthly payment. Before relying on an incentive, verify the current administrator, eligibility and documentation. Request a revised total if a selection or scope changes; a verbal assurance that it will be about the same leaves the actual commitment unclear.

California hiring and local approval questions

Use the Contractors State License Board resources below to check applicable licensing and the contracting business. Ask about relevant insurance, supervision and whether subcontractors perform any of the work. The person giving the estimate, the licensed business and the person arriving at the home may have different roles, so identify responsibility in the agreement.

Confirm the permitting authority for the property address. An incorporated city and an unincorporated county area can have different departments even when the mailing city looks the same. Ask who determines required approvals, who obtains them and who provides final inspection records. Do not interpret a contractor saying no permit needed as a substitute for an explanation tied to the actual scope and local requirements.

Document completion and resolve changes

For discoveries or changes, request the condition found, supporting evidence, added scope, price and schedule effect before authorization. Retain the agreed change with the original contract. A product substitution should identify the replacement and any effect on performance, fit or coverage rather than merely saying equivalent.

At the walkthrough, compare the delivered result with the agreement and keep a written list of unresolved items. Collect operating instructions, inspection records when applicable, warranty terms and final invoices. Record who handles a callback and how to contact them. If the original symptom returns, refer back to the diagnosis and completion records rather than assuming a new unrelated problem.