Most San Jose single-family properties are candidates for some type of ADU, but setbacks, easements, utilities, and access determine what can fit and how large it can be. A garage conversion, attached unit, or smaller detached ADU may work where a preferred backyard layout does not. Check the property and the applicable approval path before paying for a complete set of plans.
A useful feasibility review answers two different questions: can the project qualify for approval, and can it be built within your budget and practical constraints? A favorable answer to one does not settle the other. Start with records and a measured sketch, then investigate the issues that could change the concept.
Confirm the property’s jurisdiction and records
A San Jose mailing address does not necessarily establish that the property is inside the city. Use SJPermits.org to check jurisdiction, zoning, property descriptions, and available permit history. If the parcel is in unincorporated Santa Clara County or another city, a different local process applies.
San Jose’s ADU Universal Checklist begins with jurisdiction, a legally permitted main residence, and active code-enforcement issues. Review those questions before assuming an existing structure is legal because it has been there for years. Missing records or an open case may require clarification before design moves forward.
Gather a parcel map, available survey, title information, existing floor plans, and past permits. A fence is not proof of a property boundary, and an assessor’s sketch is not a substitute for a survey when precise setbacks matter. Mark uncertain dimensions as uncertain rather than building a design around them.
Compare the four common ADU approaches
A detached ADU is a separate dwelling with its own living facilities. It can provide privacy and flexibility, but it also needs a location, foundation, utility route, and construction access. An apparently empty corner may contain a sewer easement or protected tree roots.
An attached ADU connects to the main house while functioning as a separate dwelling. It can make use of a logical expansion area, but the design needs to address the connection, entrances, privacy, and building separation requirements where applicable.
A garage conversion uses an existing structure. That may save some construction, but the slab, ceiling height, moisture conditions, framing, and utility capacity still need assessment. A garage that is suitable for storage is not automatically suitable for housing.
A junior ADU, or JADU, is a smaller unit within a single-family home’s permitted framework, including qualifying attached-garage space. Its kitchen, sanitation, occupancy, and deed-restriction rules differ from those for a full ADU. Do not assume the smallest option is simply a detached unit with fewer rooms.
Read size limits and setbacks as a complete standards path
San Jose’s current published checklist distinguishes City development standards from State development standards. Pick the applicable path with your designer and City reviewer; do not combine the most generous individual provisions from both tables.
For an initial comparison, the checklist’s City table lists new detached ADU maximums of 1,000 square feet on lots below 9,000 square feet and 1,200 square feet on larger lots. Its State table lists an 800-square-foot new ADU option with four-foot side and rear setbacks. JADUs are listed at up to 500 square feet. If your lot is exactly 9,000 square feet, confirm its treatment directly rather than guessing from the table’s labels.
The City path also lists zero-foot first-story side and rear zoning setbacks for detached units, subject to other conditions; the State path’s four-foot rule is a different framework. Zero zoning setback does not mean ordinary windows, eaves, or wall construction are automatically acceptable at a property line. Building and fire requirements still matter.
The linked checklist contains additional siting, separation, height, and conversion provisions. These figures are a screening tool, not a parcel-specific approval. Confirm the version and interpretation when you apply, especially if your design depends on an exception.
Check easements, trees, and slope before drawing the footprint
Read the title report and recorded documents for utility, access, drainage, and other easements. Show them on the concept plan and ask the relevant easement holder what construction is allowed. A zoning setback rule does not erase a recorded right to access an underground line.
Inventory significant trees, including trees on neighboring land whose roots may extend into the project area. Tree protection, excavation limits, or a removal permit can change the buildable footprint. Do not assume removing a tree is a routine site-clearing item; consult the City’s tree guidance and an arborist where needed.
Slope affects foundation design, grading, drainage, and how materials reach the site. Check the City’s flood, geohazard, landslide, and other mapped designations. A hillside lot is not automatically infeasible, but its studies and construction scope may be quite different from those of a flat lot.
Locate sewer, electrical, and water services
Sketch the likely utility routes rather than just the unit itself. For sewer, identify the existing lateral, connection location, approximate depth, and whether the proposed route can achieve the required drainage design. A camera inspection or other investigation may be worthwhile when the condition or route is uncertain.
For electricity, have a qualified professional assess the house and ADU loads, existing service, panel condition, and proposed metering arrangement. Ask whether PG&E work is likely and when an application should begin. A nearby electrical panel is not proof that it can supply another dwelling.
For water, confirm the provider, existing service, meter capacity, pressure, and any required fire-flow documentation. San Jose’s checklist and permitting resources identify fire-access and hydrant considerations; verify those with the relevant reviewers rather than assuming a new water meter is always required.
Keep utility questions separate from assumptions about fees. A concept may fit physically but require costly trenching or an upgrade. Get the unresolved items into the feasibility report before treating an early construction allowance as a confirmed price.
Check whether crews and equipment can reach the site
Measure the side-yard route, gates, overhead obstructions, turns, and places to stage materials. Include the occupied house, parking, neighbors, and waste removal in the access plan. A workable route for a person may not be a workable route for excavation equipment.
Restricted access can change how the foundation is built, how concrete is placed, and how much labor the project needs. Prefabricated units may require delivery and crane access that a site-built approach does not. Conversely, an accessible lot may be well suited to factory-built installation.
Construction access is also different from the permanent path needed for occupants and emergency response. Ask the designer to show both. If a plan relies on neighboring property, establish the necessary permission before using that access as a design assumption.
What a useful feasibility visit should include
The visit should connect your goals to a preliminary site plan and a list of verified constraints. Walk the proposed footprint, inspect accessible existing structures, review utility locations, and discuss privacy, outdoor space, and the household’s intended use of the ADU.
Ask for written deliverables: feasible unit types, an approximate size range, the proposed standards path, likely utility work, access assumptions, and the next investigations. The report should distinguish observations from items requiring a survey, engineer, arborist, utility response, or City determination.
A sensible next step may be a smaller concept, a conversion comparison, or a focused investigation before detailed architecture. Feasibility is valuable because it helps you decide what to investigate next; it should not be presented as a building permit or a guaranteed construction price.
Frequently asked questions
Is a large backyard enough to qualify?
No. The main residence, jurisdiction, standards path, easements, utilities, and access all need review. A large open area can still contain a constraint that changes the design.
Can I use a preapproved ADU plan?
Possibly. San Jose offers preapproved plans, but the site still needs to qualify and the package must address property-specific conditions. Preapproval of a design is not approval of every location.
Does a garage conversion avoid all setbacks?
Existing-space conversions have different provisions from new construction. Confirm the structure’s legal status and the applicable building, fire, and conversion rules before relying on its existing location.
Should I order a survey before a consultation?
Bring any survey you already have. Your team can identify whether new boundary or topographic work is needed; do not assume a quick field measurement resolves a disputed or uncertain property line.
Start with a site visit
If you are considering an ADU in San Jose, EDR Design Build can discuss a feasibility site visit and the records worth gathering first. The goal is to identify a realistic direction before you invest in detailed plans.
Request a consultation:
https://www.edremodel.com/contact
Official sources reviewed October 27, 2026:
https://www.sanjoseca.gov/home/showpublisheddocument/39038/639083231101130000
https://www.sanjoseca.gov/business/development-services-permit-center/accessory-dwelling-units-adus
