Buying a San Jose Home With an ADU: What to Verify Before You Offer

If the San Jose home you're considering already has an accessory dwelling unit, or you're hoping to add one later, the question that matters most isn't whether you like it. It's whether the unit is legally permitted, and whether the lot can actually support one under current law. Before you write an offer, pull the property's permit history through the City of San Jose's online permit system, confirm the unit's size and layout match what's on file, and ask your lender whether rental income from it can count toward your mortgage. Skipping this step is the most common ADU mistake I see San Jose buyers make.

What Counts as an ADU or a JADU in San Jose?

An accessory dwelling unit (ADU) is a second, independent living space on a residential lot with its own kitchen, bathroom, and entrance. It can be detached from the main house, attached to it, or converted from existing space like a garage.

A junior accessory dwelling unit (JADU) is smaller and built entirely within the walls of the existing single-family home. State law caps a JADU at 500 square feet of interior living space, and it's allowed to share a bathroom with the main residence.

Under California's ADU Handbook, published by the state Department of Housing and Community Development (HCD), a newly built detached ADU generally has a floor of 800 square feet of interior living space that a city must allow regardless of other zoning limits, with larger sizes often possible depending on the lot. According to the City of San Jose's ADU page, San Jose enacts state ADU and JADU law directly into its own zoning code, so the statewide rules are, with narrow exceptions, the rules that apply on your specific San Jose lot.

Does This Home Already Have an ADU, and Is It Permitted?

You find out by searching the property's exact address or Assessor's Parcel Number in the city's SJPermits.org system, before you remove any contingencies.

The lookup shows the status of permits tied to the property, including building permits, and whether a project was ever marked "Finaled," which is the city's confirmation that inspections were completed and closed out. If you see permit history for the main house but nothing tied to a second structure or a converted garage, that's a sign the unit may never have been permitted.

It's also worth comparing what you find to the Santa Clara County Assessor's recorded living area and bedroom or bathroom count for the parcel. An ADU that was built without permits is sometimes missing from that record entirely, which is itself a red flag worth raising with the listing agent before you write an offer.

What Happens If the ADU Isn't Permitted?

An unpermitted ADU doesn't automatically rule out the home, but it changes how you should structure your offer, your financing, and your plans after closing, because you're the one who inherits the legalization work unless the seller handles it first.

Since January 1, 2025, a state law commonly referred to as AB 2533 has created a narrower path for owners to legalize ADUs and JADUs that were originally built before January 1, 2020. Under this law, cities cannot deny a legalization permit based on today's setback, size, or height standards. They can only require the unit to meet the health and safety standard defined in California Health and Safety Code Section 17920.3, and they're barred from charging impact or utility connection fees for that legalization, according to regional planning guidance on the law from the Association of Bay Area Governments and Metropolitan Transportation Commission. Units built in 2020 or later don't qualify for this path and generally need to meet current code in full.

As a buyer, ask when the unit was actually built, not just when the seller says it was built. Escrow documents, prior permits, tax records, and dated photos can help establish this. If it predates 2020 and was never permitted, you have two real options: ask the seller to start or complete AB 2533 legalization before closing, or negotiate a credit that reflects the inspection and repair work you'll likely take on yourself.

Can You Use ADU Rental Income to Qualify for a Larger Mortgage?

Yes, for a permitted ADU. As of Fannie Mae's Selling Guide update effective October 8, 2025 (Announcement SEL-2025-08), lenders can count projected or actual rental income from a legally permitted ADU toward mortgage qualification on a one-unit, owner-occupied purchase, documented with either a signed lease or an appraiser's opinion of fair market rent on Form 1007 or Form 1025.

This only applies to ADUs the appraiser and lender can verify as legally permitted, and not every lender has updated its underwriting process at the same pace. If ADU income is part of how you plan to qualify, raise it with your lender before you write the offer, not after you're in contract with a financing contingency deadline approaching.

If There's No ADU Yet, What Should You Know Before You Buy to Build One?

You don't need to live on the property to build a standard ADU. State law removed the owner-occupancy requirement for ADUs; it only applies to a JADU that shares sanitation facilities with the main house, per HCD's ADU Handbook.

Once you submit a complete application, San Jose has up to 60 business days to approve or deny it, following a 15-business-day window to confirm the application is complete. Parking is often not required for an ADU when the lot sits within a half mile of public transit, among other state law exemptions, so check your specific lot rather than assuming either way. San Jose also runs a preapproved ADU plan program that can simplify permitting for homeowners who build to one of the city's pre-vetted designs.

Will Your HOA Let You Build or Keep an ADU?

Generally yes, if the community is a single-family or multifamily common interest development. California Civil Code Section 4751, enacted through AB 670, bars HOAs from adopting or enforcing rules that unreasonably restrict ADU or JADU construction. An association can still apply reasonable restrictions tied to aesthetics, such as matching the main structure, placement, such as setback compliance, or safety, but it generally cannot use CC&Rs to block an ADU outright.

Because what counts as "reasonable" has been tested in court and can vary by association, have a real estate attorney review your specific CC&Rs before you count on ADU rights in an HOA community. This is general information, not legal advice on your specific documents.

How This Fits Into the Rest of Your Due Diligence

ADU verification is one piece of a larger due diligence process, not a substitute for it. A general home inspection still matters for evaluating the condition of an existing ADU, and a preliminary title report can surface easements or use restrictions that affect where a new ADU could go. If the property is a condo or townhome, review the HOA documents closely, since ADU rights work differently in attached communities than on a single-family lot.

If your goal is rental income rather than a place for family, it's worth running the numbers the way any San Jose investment property should be evaluated. My guide to calculating ROI and cash flow on San Jose rental properties walks through that process, and my San Jose real estate investing guide covers the broader strategy.

I work with both buyers and sellers across San Jose, and I bring the same verify-first approach whether you're evaluating an ADU on a home you want to buy or figuring out how one affects your home's value before you sell.

Quick ADU Verification Checklist Before You Offer

• Search the address or Assessor's Parcel Number in San Jose's permit system for any ADU-related permit history
• Confirm whether a permit, if one exists, shows a "Finaled" status
• Compare the physical unit to the county assessor's recorded living area and bedroom or bathroom count
• Ask the listing agent directly when the unit was built and whether it was ever permitted
• If unpermitted and built before 2020, discuss AB 2533 legalization with the seller or your agent before removing contingencies
• Confirm with your lender, in writing, whether ADU rental income can count toward your qualification
• If the property is in an HOA, have an attorney review the CC&Rs for ADU-specific restrictions

Frequently Asked Questions

What's the difference between an ADU and a JADU?

An ADU is a full second unit with its own kitchen, bathroom, and entrance, and it can be attached, detached, or converted from existing space. A JADU is smaller, capped at 500 square feet, built within the existing walls of the main house, and can share a bathroom with the primary residence.

Do I have to live in the main house to have an ADU in San Jose?

No, not for a standard ADU. State law removed the owner-occupancy requirement for ADUs. It only applies to a JADU when that unit shares sanitation facilities with the main house.

How do I check whether an ADU is legally permitted before I make an offer?

Search the property by address or Assessor's Parcel Number in the City of San Jose's SJPermits.org system and look for a finaled building permit tied to the accessory structure, then confirm what you find with the listing agent in writing.

Can I still buy a home with an unpermitted ADU?

Yes, but treat it as a negotiation and disclosure issue rather than a bonus room. If the unit was built before January 1, 2020, ask about the AB 2533 legalization path before you remove contingencies.

Will a lender automatically count ADU rental income toward my mortgage?

Not automatically. Since October 2025, Fannie Mae allows it for legally permitted ADUs on owner-occupied purchases, documented with a lease or an appraisal, but your specific lender still has to apply the update, so confirm it early in your process.

How long does it take to get an ADU permitted in San Jose?

State law gives San Jose up to 60 business days to approve or deny a complete ADU application, after a 15-business-day review to confirm the application is complete, according to HCD's ADU Handbook.

Zaid Hanna
408-515-1613
www.re38.com