An ADU or granny flat inspection in San Diego is a buyer’s visual evaluation of an accessory dwelling unit’s structure, electrical, plumbing, and life-safety systems, plus a hard look at whether the unit was permitted. A home inspector reports condition and visible concerns; confirming legal status requires checking county and city permit records.
Why ADUs Are Everywhere in San Diego County
Accessory dwelling units (ADUs) and junior ADUs (JADUs) have exploded across San Diego County since the state loosened the rules. You will find them as backyard cottages in Encinitas, converted garages in El Cajon, basement and bonus-room units in older La Mesa homes, and attached suites in newer San Marcos builds. The city of San Diego’s own bonus ADU program has pushed density even higher in transit corridors.
For a buyer, an ADU can be a genuine asset: rental income, a space for aging parents, or a home office. But it can also be a liability if it was built without permits, wired by a weekend handyman, or converted in a way that violates life-safety code. The unit that looks charming on a Saturday showing may be the part of the property that costs you the most after closing. That is why an ADU deserves the same scrutiny as the main house, and often more.
The Permit and Legality Question Comes First
Before condition, ask about legality. A “permitted” ADU was built or converted with approved plans and signed-off inspections. An “unpermitted” unit may still be standing and rented, but it carries real risk: a future buyer’s lender may not count its income, the county may not recognize the bedroom count, and you could be ordered to bring it to code or remove it.
A home inspector is not a permit authority and does not certify legality. What an inspector can do is flag signs that a space was converted without proper oversight, such as a garage with no firewall, bedroom-style wiring run on the surface, or a kitchen plumbed into drains never sized for it. To verify legality, you or your agent should:
- Pull permit history from the city or county building department for the property address
- Compare the recorded square footage and unit count to what you see on site
- Ask the seller for the final sign-off card or certificate of occupancy for the ADU
- Confirm with the local jurisdiction whether the unit is a legal ADU, JADU, or simply a finished space
Treat any “it was permitted, I just can’t find the paperwork” answer as a reason to dig deeper, not to relax.
What an ADU Inspection Actually Covers
A thorough inspection treats the ADU as a separate dwelling. Whether the unit is detached, attached, or a garage conversion, the inspector evaluates the same accessible systems a buyer’s home inspection covers on the main house, then pays extra attention to the issues conversions tend to create.
Structure and the building envelope
Detached cottages get checked for foundation movement, roof condition, and proper drainage away from both the ADU and the main house. Garage conversions are scrutinized for whether the slab, framing, and roof were ever meant to be living space. Many older San Diego garages have minimal insulation, an uninsulated roll-up door opening framed over, and grade that slopes water toward the structure.
Electrical and sub-panels
Electrical is where conversions most often go wrong. ADUs are frequently fed from the main home’s panel through a sub-panel, and the quality of that work varies wildly. An inspector looks for an appropriately sized feeder, correct separation of neutrals and grounds in the sub-panel, GFCI and AFCI protection where required, and no extension-cord-grade wiring buried in walls. If the main house is older, the existing service may be marginal even before an ADU is added on. Our guide to electrical panel problems in older San Diego homes walks through the dated equipment we still see across the county.
Plumbing and water heating
The inspector checks supply and drain functionality, looks for proper venting, and notes whether the ADU has its own water heater and whether it is sized and secured correctly. Garage and basement conversions sometimes route a new kitchen or bathroom into drain lines that were never designed for that load.
Heating, cooling, and ventilation
Each habitable unit needs a permanent heat source and adequate ventilation. Space heaters and window units are red flags for a conversion that skipped permitting. Bathrooms and kitchens should exhaust to the exterior, not into an attic or the garage attic shared with the main house.
Life-Safety Items That Cannot Be Compromised
Some findings are about comfort. Others are about whether the unit is safe to sleep in. On every ADU, an inspector pays close attention to:
- Egress: sleeping areas need a code-compliant way out, typically a door or an emergency escape window of adequate size and sill height
- Smoke and carbon monoxide alarms: required in the ADU as its own dwelling, not just the main house
- Fire separation: garage conversions and attached units have firewall and self-closing-door requirements that are often missing after a DIY conversion
- Ceiling height and light: habitable rooms have minimum height and natural-light standards a finished-but-unpermitted space may fail
- Gas appliance clearances and venting: water heaters and furnaces tucked into closets or former garages need proper combustion air and venting
Separate Utilities and Metering
Buyers planning to rent the ADU should understand how it is served. Some San Diego units have separate gas and electric meters; many share the main home’s service. Shared utilities are legal and common, but they complicate billing a tenant and can hide whether the existing service has capacity for two households. The inspector documents what is visible; how you handle cost-splitting is a conversation for your agent and, if rented, a landlord-tenant question worth professional advice.
Specialty Concerns Beyond a General Inspection
A general home inspection is visual and broad. Some ADU issues call for a specialist, and a good inspector will tell you when to bring one in. Garage conversions in homes built before the late 1970s may involve materials that warrant testing for asbestos or lead by a qualified lab. Damp basement and below-grade conversions can show moisture and possible microbial growth that a mold professional should assess. Wood-destroying organisms are evaluated by a licensed structural pest operator, not a home inspector, so we coordinate or recommend one when conditions suggest a closer look. A sewer scope is also smart on any property where new fixtures were added to old drain lines.
Make ADU Due Diligence Part of Your Offer
If you are buying a San Diego home with an ADU, treat the unit as a second property within the deal. Verify permits with the jurisdiction, get the whole property inspected by a qualified inspector, and use what you learn to negotiate or walk away. For more on protecting yourself, see our home inspection red flags and deal breakers and what to do after your home inspection.
The Real Estate Inspection Company inspects homes and ADUs across all of San Diego County. Owner and lead inspector Joseph Romeo is an InterNACHI Certified Professional Inspector and holds CSLB General Contractor License #1113143. Call (619) 752-4399 or contact us to schedule, and check the fee schedule since pricing depends on square footage, age, and access.
