Should You Buy an ADU Property as an Investment?

Nov 24, 2026 · By Oanh Nguyen · Broker & Loan Officer · Investing

A home with an accessory dwelling unit, or ADU, can look like two rentals for the price of one. A main house and a backyard cottage. A garage conversion. A unit over the garage. More income from one lot.

Sometimes it works out that way. Sometimes the "ADU" turns out to be an unpermitted room, the utilities are shared in ways that cause problems or the rent doesn't cover the extra costs.

In this post, I'll walk through what to check before you assign value to an ADU: the types of ADUs, permit verification, rent assumptions, construction and maintenance, access and utilities, financing and a due diligence checklist.

This is general education. It isn't legal, tax or investment advice. ADU rules come from state law and city rules, and both change. Always confirm current rules with the city and the state's official resources.

What Is an ADU?

An ADU is a secondary home on the same lot as a main home. California law has encouraged ADUs for years, and the state housing department, HCD, publishes an ADU Handbook that explains the state rules. HCD updated its handbook in March 2026 and added an addendum summarizing changes in effect January 1, 2026.

Common types:

• Detached ADU: a separate building, like a backyard cottage.
• Attached ADU: connected to the main home, often as an addition.
• Converted ADU: created from existing space, like a garage or basement.
• Junior ADU (JADU): a smaller unit within the main home's footprint. San José, for example, describes JADUs as under 500 square feet and within a single-family home.

Each type has different costs, privacy levels, permit paths and rental appeal.

Step 1: Verify Legal Status and Permits

This is the most important step. An ADU only adds reliable value if it's legal.

What to check:

• Permit records with the city building department. Was the ADU permitted and finaled?
• Certificate of occupancy or final inspection sign-off, where applicable.
• Seller disclosures. Did the seller disclose the unit and its permit status?
• County assessor records. Do they reflect the unit?
• Utility setup. Does it match the permitted plans?

Why it matters:

• Unpermitted units can affect financing, appraisal and insurance.
• The city may require changes or removal of an unpermitted unit.
• Renting an unpermitted unit can raise legal issues. Talk with an attorney.
• Some cities have programs to legalize older unpermitted units. San José, for example, has a page on its ADU and JADU legalization program under state law AB 2533. Requirements, costs and timelines vary.

If permits are missing or unclear, don't count the ADU's rent in your numbers until you know the path and cost to make it legal.

Step 2: Rent Assumptions

ADU rents depend on size, privacy, layout, parking, outdoor space and condition.

How to estimate:

• Look for leased comps of similar ADUs, cottages or small units nearby.
• Compare privacy features: separate entrance, separate yard, sound separation.
• Consider parking. Some ADUs have none.
• Check utilities. Are they included in rent or separately metered?
• Be careful with short-term rental assumptions. Many cities restrict short-term rentals, and some ADU rules limit them. Check city rules.

Rent rules may also apply. California has a statewide rent cap law for many properties, and some cities have their own rules. Whether they apply to a specific ADU depends on the property and the law. Check official sources and talk with an attorney.

Step 3: Construction Quality and Maintenance

Not all ADUs are built the same.

Inspect:

• Foundation and framing.
• Roof and drainage.
• Electrical service and panel capacity. Can the main home and ADU share it safely?
• Plumbing and sewer connection.
• Heating, cooling and ventilation.
• Insulation and soundproofing between units.
• Fire safety features, like smoke and carbon monoxide alarms and egress windows.

Maintenance considerations:

• Two units mean two sets of appliances, fixtures and systems to maintain.
• More tenants can mean more wear and more management.
• Shared systems, like a single water heater or sewer line, can create issues for both units.

Budget for higher maintenance and capital expenses than a single-unit property.

Step 4: Access and Utilities

These details can make or break an ADU's rental appeal.

Access:

• Is there a separate, safe path to the ADU?
• Does the tenant need to walk through the main home's yard?
• Is there lighting along the path?
• Is there parking?

Utilities:

• Separate meters or shared?
• If shared, how will you split costs fairly and legally?
• Is the electrical and water service big enough for both units?
• Internet and trash service.

Shared utilities can lead to disputes and lower rent. Separate meters can cost money to install but may make the unit easier to rent and manage.

Step 5: Financing

Financing a property with an ADU has its own wrinkles.

• Appraisal: How the appraiser treats the ADU depends on its legal status, comparable sales with ADUs and the loan program.
• Rental income: Whether a lender counts ADU rent toward your qualifying income depends on the program's rules. Some programs have specific guidance on accessory unit income. Ask your lender.
• Property type: A home with an ADU may be treated differently from a duplex. Ask how the lender classifies it.
• Unpermitted units: These can create appraisal and lending problems.

I'm a licensed loan officer, so I can help you understand how different programs may treat an ADU property. This isn't a loan offer, and approval depends on a full review.

Step 6: Due Diligence Checklist

• ☐ Pull city permit records and final inspection sign-offs.
• ☐ Review seller disclosures for the ADU.
• ☐ Check county assessor records.
• ☐ Review the HCD ADU Handbook and the city's ADU page for current rules.
• ☐ Inspect both units, including electrical capacity and sewer.
• ☐ Confirm utility metering and service size.
• ☐ Confirm access, parking and privacy.
• ☐ Pull leased comps for the ADU and main home separately.
• ☐ Check rent rules and short-term rental rules with official sources.
• ☐ Review existing leases if occupied.
• ☐ Get insurance quotes that cover both units.
• ☐ Ask your lender how the ADU will be appraised and whether its rent counts.
• ☐ Talk with your CPA about tax effects and your attorney about legal questions.

Buying a Lot to Build an ADU Instead

Some investors buy a home planning to add an ADU. That's a different strategy, closer to a renovation project.

Consider:

• Zoning and lot fit. Does the lot allow the ADU you want?
• Construction costs and timeline. Get bids from licensed contractors.
• Permit timeline.
• Utility connections and fees.
• Financing for construction.
• Holding costs while you build.

My post on rental property vs. fixer-upper covers the trade-offs of renovation strategies.

Living in One Unit and Renting the Other

Some buyers purchase a home with an ADU, live in one unit and rent the other. This is sometimes called "house hacking."

Why buyers consider it:

• Rent from one unit can help with housing costs.
• It can be a first step into real estate investing.
• It offers flexibility for family members later.

What to think about:

• Financing is different when you live in the property. Loan programs for a primary home have their own rules on counting accessory unit income. Ask your lender.
• Privacy and boundaries. Living next to your tenant takes clear communication and a written lease.
• Landlord responsibilities still apply, even when the tenant is in your backyard.
• Rules may differ depending on whether the owner lives on site. Check city rules and talk with an attorney.

Questions to Ask the Seller About the ADU

• When was the ADU built or converted, and by whom?
• Was it permitted and finaled? Can you share the records?
• Are utilities separately metered?
• Has it been rented? At what rent, and for how long?
• Are there any known issues with the unit?
• Were there any complaints or notices from the city?

Pros and Cons of ADU Properties

Potential pros:

• Two income streams on one lot.
• Flexibility: rent both, live in one, or house family.
• Possible broader buyer appeal on resale.

Potential cons:

• Permit and legal status risks.
• Higher maintenance and management.
• Shared utilities and privacy issues.
• Financing and appraisal complexity.
• Local rules that change.

A Hypothetical Example

This example is made up to show the process. It is not based on any real property or client.

An investor finds a single-family home listed with a "rentable backyard studio." The listing shows strong combined rent.

We pull permits. The studio was permitted as a home office, not a living unit. There's no kitchen permit, and the plumbing was added later.

The investor runs two sets of numbers: one with the main home only, and one with the studio after legalization costs. They talk with the city about the legalization path and get a contractor estimate. The numbers only work at a lower price. They make an offer based on the main home's value alone, with the studio as possible upside. The seller declines, and the investor moves on without overpaying for an ADU that wasn't really an ADU.

Frequently Asked Questions

The Bottom Line

An ADU property can add income and flexibility, but only if the ADU is legal, well built and rentable at a price that covers the extra costs. Verify permits before you count any ADU rent. Inspect both units. Check utilities, access and parking. Ask how your lender will treat the unit. And confirm current state and city rules.

Looking at a property with an ADU? Let's review it before you make an offer. I'll help you check permits, comps and financing so you know what you're really buying.

Sources

• California Department of Housing and Community Development (HCD), ADU Handbook (updated March 2026): https://www.hcd.ca.gov/building-standards/adu/handbook
• City of San José, Accessory Dwelling Units (ADUs): https://www.sanjoseca.gov/business/development-services-permit-center/accessory-dwelling-units-adus
• City of San José, AB 2533 ADU and JADU Legalization Program: https://www.sanjoseca.gov/businesses/development-services-permit-center/accessory-dwelling-units-adus/ab-2533-adu-and-jadu-legalization-program
• California Attorney General, Limits on Rent Increases: https://oag.ca.gov/rentcaps
• Contractors State License Board, Hire a Contractor: https://www.cslb.ca.gov/Consumers/Hire_A_Contractor/

Review an ADU property before you offer. Call or text me at 408-780-1188, or email onrealtygroup@gmail.com.

Oanh Nguyen · Broker & Loan Officer · On Realty Group, brokered by LPT Realty · BRE #02133991 · NMLS 2020335

Equal Housing Opportunity.

Loan disclosure: Oanh Nguyen, Broker | Loan Officer, On Realty Group, brokered by LPT Realty, BRE #02133991, NMLS #2020335. This post is general education, not a loan offer, rate quote or commitment to lend. Loan programs, guidelines and eligibility change and are subject to lender review and approval.

Disclaimer: This post is general information only, not an appraisal or legal, tax or financial advice; data comes from the public sources linked above, is believed reliable but not guaranteed, and can change at any time.