ADU Builders in
San Jose, CA

San Jose homeowners have more than one design path: a custom ADU, a plan from the city's approved preapproved-plan gallery, or a conversion of eligible existing space. The best builder is not simply the one with the lowest starting price. It is the company that can explain which path fits the property, put every site and utility assumption in writing, and show who owns each step from feasibility through final inspection.

This guide compares three San Jose ADU builders using builder-published local-service evidence and dated California Contractors State License Board checks. It also separates the city's preapproved-plan route from the property-specific work that every address still needs.

Compare San Jose ADU builders

All three companies below are Basic listings. They did not pay for placement, and ADU Builder Hub does not endorse or guarantee their work. Use the evidence as a starting point, then verify the current license, insurance, references, contract scope, and availability before signing.

Builder	Public San Jose evidence	Published scope	What to ask first
Acton ADU	Publishes a San Jose-specific service page covering its local design-build process. CSLB license 638333 was checked current and active on August 19, 2026.	Design, permitting, and construction.	Will the proposal price a city-approved plan and a custom plan against the same site assumptions?
OT Bay Builders	Publishes a San Jose ADU page and lists a San Jose office. CSLB license 1097881 was checked current and active on August 19, 2026.	Architectural drawings, permit applications, design, and construction.	Which utility, grading, and permit costs are fixed, allowances, or excluded?
Blackstone Construction	Publishes ADU design-build services, a San Jose office, and San Jose project examples. CSLB license 1126133 was checked current and active on August 19, 2026.	In-house design and construction.	Who signs the plans, who answers city corrections, and what happens when site conditions change?

The table does not rank workmanship, price, speed, or customer satisfaction. Those claims need project-specific evidence that public service pages and license records cannot provide. Ask each company for recent San Jose references whose project type resembles yours, then use the same written questions for every bid.

Start with the city's property checklist

Start with San Jose's current ADU Universal Checklist. It is the city's practical screen for the proposed unit, property, setbacks, access, utilities, fire conditions, and other address-specific constraints. California's ADU handbook explains the statewide framework, but the city still reviews the actual site and permit package.

Homeowner question	Current San Jose check
Can I use a preapproved plan?	San Jose maintains a gallery of approved plans for eligible properties. The plan design is reviewed in advance, but the property and site documents are not.
Does preapproved mean permit-ready anywhere?	No. The city still requires a complete site-specific submittal. Hazard, fire, flood, utility, clearance, and property conditions can change the route.
Is every plan shown on the city page approved?	No. San Jose separates approved plans from plans that are still under review. Confirm the plan's current status in the approved gallery before buying it.
Can the permit be issued during plan review?	San Jose says a same-day permit may be issued at a scheduled plan-review appointment when the package is complete and the project qualifies. Deferred structural work, clearances, or variances take longer.
What if an ADU was built without permits?	San Jose publishes a separate AB 2533 legalization program for qualifying ADUs and JADUs built before January 1, 2020. That is not the same route as a new ADU permit.

Preapproved is faster, not site-free

San Jose's preapproved ADU program standardizes the building plan, not the lot. The city says site-specific documents are still required, and eligibility is limited. A property in a geohazard, landslide, flood, or wildland-urban interface area may not qualify for the streamlined route.

The city also publishes plans that are currently under review. A vendor's appearance in that section does not mean its plan is approved. Before paying a plan vendor or builder, save the dated city page that shows the selected design in the approved gallery and ask who pays if the site cannot use it.

Choose the route before fixing the budget

A preapproved plan can reduce building-plan review work, but it does not eliminate survey, site plan, utility, foundation, drainage, fire, tree, or clearance questions. A custom plan costs more to develop but may use a constrained lot better. A garage or interior conversion can avoid a new detached footprint while introducing structural, moisture, ceiling-height, fire-separation, and utility questions.

Ask the designer or builder for a short feasibility memo before final drawings. It should identify the proposed ADU type, city route, plan source, site constraints, utility assumptions, required outside consultants, and open questions. If the team will not put those assumptions in writing, the price is not ready to compare.

How to compare builder proposals

Three bids are useful only when they describe the same job. Give every builder the same property facts, desired unit, finish level, plan route, and target use. Ask them to return the proposal in the same categories.

Proposal section	What should be explicit
Feasibility	Survey needs, zoning and checklist review, site constraints, utility capacity, fire access, trees, drainage, and geotechnical questions.
Design	Preapproved plan license or custom architecture, structural engineering, energy documents, civil work, plan ownership, and revision limits.
Permitting	Application preparation, city appointments, plan-check responses, outside-agency clearances, permit fees, and the person responsible for each correction.
Site and utilities	Demolition, access, excavation, foundation, sewer, water, electrical service, trenching, meters, drainage, and restoration.
Construction	Labor, materials, finishes, appliances, project management, inspections, cleanup, warranty, and completion documents.
Uncertainty	Allowances, exclusions, escalation terms, concealed conditions, change-order approval, and schedule dependencies.

Do not compare an early estimate from one builder with a construction-ready proposal from another. Mark every allowance and exclusion, then ask what evidence would turn each unknown into a fixed amount. Use the California ADU cost guide to build a complete budget before treating a construction number as the project total.

Questions worth asking all three builders

• Which San Jose ADU projects have you completed under the current process, and may I speak with two recent owners?
• Is the proposed design already approved by the city, currently under review, or fully custom?
• Who is the designer of record, and who answers plan-check comments?
• Which utility, foundation, drainage, tree, fire, and access assumptions are included in the price?
• Which fees and consultant costs are excluded?
• What milestone must be reached before the construction price becomes fixed?
• How are schedule changes and owner-requested changes documented?
• What insurance, warranties, lien releases, inspection records, and closeout documents will I receive?

San Jose does not publish one construction price that applies to every ADU. Plan route, lot access, utilities, foundation, finish level, energy requirements, and outside-agency work can move the total substantially. Treat any advertised starting price as a scope-specific marketing figure, not a city estimate.

Build the budget from six parts: feasibility, design and engineering, permit and agency costs, site and utility work, vertical construction, and contingency. Keep financing costs and temporary housing separate so they do not disappear from the decision.

A preapproved plan may reduce some design and review work, but the savings can be offset when the site needs structural changes, utility upgrades, a different foundation, or additional clearances. Ask for two written scenarios when both routes are viable: the approved plan on the actual property and a custom design with the same size and finishes.

San Jose's ADU plan review and permit process starts before plan upload. The city directs homeowners to use the Universal Checklist, gather basic planning feedback, prepare complete documents, use the Application Wizard and SJPermits, upload through SJePlans, answer comments, and complete inspections.

Use the California ADU permit checklist to organize the statewide rules and review stages, then add San Jose's property-specific requirements.

• Confirm the jurisdiction and property facts. Verify that the address is inside San Jose, then review zoning, easements, hazards, utilities, trees, fire access, and existing permits.
• Complete the Universal Checklist. Use it to identify the viable ADU type, basic standards, and questions that need city feedback.
• Choose approved or custom plans. Confirm the current status of any plan in the city's gallery and test it against the actual lot.
• Prepare the site-specific package. Add the site plan, structural and energy documents, utility information, clearances, and any required specialist work.
• Submit through the city systems. Follow the Application Wizard, SJPermits, and SJePlans instructions for the selected project route.
• Attend review and answer comments. San Jose says incomplete plans are not processed, so make ownership of every correction clear before submission.
• Issue permits, build, and inspect. Complete the required inspections and final approvals before occupancy.

What same-day permit issuance means

The city says a same-day permit may be issued at the scheduled plan-review appointment for a qualifying preapproved-plan project with a complete package. It is not a same-day design, site review, utility approval, construction, or occupancy promise. Projects with deferred structural work, additional clearances, or variances will take longer.

Ask the builder to separate four dates in the schedule: complete package ready, city appointment, permit issued, and construction complete. Combining them into one "permit timeline" hides the work and dependencies between them.

Do not justify the project with a Bay Area rent average or a builder's example. Use current long-term San Jose leases for units that match the proposed bedrooms, size, location, privacy, parking, utilities, outdoor space, and condition.

For a conservative model, use the lower end of comparable leases, subtract vacancy, maintenance, insurance, utilities paid by the owner, management, and reserves, then compare the remaining annual amount with the full project budget and financing cost. Run a second case with no rent during delays. An ADU can still make sense for family housing or flexible space even when the rental return alone does not support the project.

How do I choose among San Jose ADU builders?

Give at least three licensed builders the same property facts and written scope. Compare recent San Jose references, design responsibility, permit work, utilities, exclusions, allowances, insurance, change orders, schedule dependencies, and closeout documents before comparing totals.

Does San Jose have preapproved ADU plans?

Yes. San Jose publishes a gallery of approved plans for eligible properties. The building design is reviewed in advance, but every project still needs site-specific documents and review.

Are plans under review the same as preapproved plans?

No. The city lists plans that are currently under review separately from approved plans. Confirm that the exact design appears in the approved gallery before buying it as a preapproved option.

Can a San Jose preapproved ADU get a same-day permit?

San Jose says a qualifying project may receive a same-day permit at its scheduled plan-review appointment when the package is complete. That statement does not cover design preparation, site work, clearances, construction, inspections, or projects needing deferred structural work or variances.

What should a San Jose ADU builder include in the bid?

The proposal should separate feasibility, design, engineering, permits, city corrections, site work, utilities, construction, finishes, allowances, exclusions, contingency, and change-order rules. Ask who owns each step and when the price becomes fixed.

Can I legalize an older unpermitted San Jose ADU?

San Jose publishes an AB 2533 program for qualifying ADUs and JADUs built before January 1, 2020. It has its own eligibility, evidence, safety review, and permit process, so do not use a new-ADU proposal as a substitute for legalization advice.

How are the listed San Jose builders selected?

The directory uses public evidence that a company serves San Jose and a dated CSLB license check. Inclusion is not an endorsement. Homeowners should verify current licenses, insurance, references, scope, and availability directly.

• San Jose preapproved ADU plans and eligibility
• San Jose ADU plan review and permit process
• San Jose ADU Universal Checklist
• San Jose AB 2533 ADU and JADU legalization program
• California HCD ADU handbook