ADU in San Jose, CA
ADU design and permitting in San Jose runs between $8,500 and $22,000 for the permit set, engineering, and city approvals, depending on whether you’re converting an existing structure or building new. Most San Jose homeowners start with us because the city’s post-war housing stock was built on former orchard land, which means soil reports and foundation engineering carry extra weight here. At Ellery ADU Studio, every project begins with a written price before any work starts, so you know the full design and permitting cost before we open a single drawing file. Call (971) 497-2402 to schedule your free estimate.
Why San Jose Homes Are Different
San Jose’s residential fabric is dominated by post-war ranch-style and California tract homes built between the late 1940s and early 1970s, when the Santa Clara Valley was still covered in prune and apricot orchards. That history shows up in two ways on every ADU project. First, lots are larger than you’d find in newer Bay Area developments: 6,000 to 9,000 square feet is common in Berryessa, East San Jose, Cambrian, and Willow Glen, which means detached ADUs often clear setback and lot-coverage thresholds without needing a variance. Second, the soil itself carries agricultural history. Many East San Jose parcels sit over former orchard land, and Santa Clara County requires soil reports for former agricultural chemical use before the building department will sign off on a new foundation. We factor that into the permit timeline from day one.
The climate shapes the work too. Evergreen, Almaden Valley, and Berryessa regularly hit the mid-90s to low 100s in summer, so insulation levels, mini-split sizing, and attic ventilation need more attention than they would in a coastal city like Santa Cruz. The frost-free winters are a genuine advantage: construction runs year-round here without weather delays, which keeps schedules predictable.
Our Main San Jose Services
Two services account for most of the ADU work homeowners call us about in San Jose: garage conversions and new detached units. Each has its own San Jose page with full pricing and process detail.
Garage Conversion ADU in San Jose
San Jose’s post-war homes frequently came with detached single-car garages already positioned near the rear property line, which makes garage conversion the most cost-efficient ADU path in the city. In neighborhoods like Willow Glen and Cambrian, these garages often sit on concrete slabs that are structurally sound enough to build on, but we still verify slab thickness and foundation condition before committing to drawings. East San Jose has a higher share of old packing sheds and utility buildings converted to garages, and those almost always need additional structural review. See the full breakdown on our Garage Conversion ADU in San Jose page.
New Detached ADU in San Jose
New detached ADUs in San Jose benefit from lot sizes that are generous by Bay Area standards: a 7,000-square-foot lot in Berryessa or Evergreen typically has room for a one- or two-bedroom unit without triggering a setback variance. The bigger consideration here is the soil. Former orchard parcels in East San Jose require agricultural-chemical soil reports before foundation permits are issued, and we handle that documentation as part of the design set. Summer heat also drives insulation and HVAC sizing decisions from the first drawing. Learn more on our New Detached ADU in San Jose page.
What happens when you call
- 1
A real person answersNo phone trees - you reach a local pro.
- 2
You get an upfront price rangeHonest numbers before anyone is dispatched.
- 3
A background-checked tech heads outLicensed & insured, dispatched right away.
- 4
You approve before work beginsNothing starts until you say go.
ADU Design & Permitting in San Jose
ADU design and permitting in San Jose typically runs $8,500 to $22,000 for the complete permit set, engineering, and city approvals, with the final number driven by soil conditions, structural scope, and whether the property needs a variance. San Jose’s older housing stock, particularly the post-war tract homes and former orchard parcels of East San Jose, means soil reports and foundation engineering show up on more projects here than in neighboring cities. The permit set is the core deliverable at Ellery ADU Studio: drawings, calculations, and documentation prepared to pass San Jose’s building department review on the first or second pass, not the fourth. Our ADU Design & Permitting process folds engineering, Title 24 energy compliance, and city submittal into one contract at one written price.
Site Assessment
Signs you need it
You have a rear yard, side yard, or existing structure you want to build on, but you don’t know whether the lot actually clears San Jose’s setback, lot-coverage, or soil requirements.
What it costs in San Jose
A site assessment in San Jose runs $450 to $1,200, and on former orchard parcels in East San Jose we pull preliminary soil data so you know the foundation line item before you commit to design.
How we do it
We measure the lot, review San Jose zoning records and any HOA restrictions, check utility connection points, and identify whether an existing structure, slab, or grading condition changes the project’s scope.
ADU Design & Blueprints
Signs you need it
You know what you want to build, but the city will not accept a sketch: San Jose requires dimensioned, engineered drawings with structural calculations and Title 24 energy documentation.
What it costs in San Jose
Full ADU design and blueprint sets in San Jose range from $8,500 to $15,000 depending on whether it’s a conversion or new construction, with add-ons like solar-ready roof framing running $1,000 to $3,000.
How we do it
We produce the architect’s drawings, structural engineering, and the documentation package in one pass, sized for San Jose’s summer heat loads rather than a generic Bay Area template.
Permit Application
Signs you need it
You have drawings in hand but have already hit two rounds of comments from San Jose’s building department, or you simply don’t want to spend months navigating the submittal process yourself.
What it costs in San Jose
Permit application services in San Jose run $2,500 to $6,500 for city submittal, response management, and final approval coordination.
How we do it
We submit the full package to San Jose, track every comment, respond with revised drawings and calculations, and stay on the file until the permit is issued.
What ADU Design & Permitting Costs in San Jose
| Item | Typical range in San Jose |
|---|---|
| Site assessment | $450 - $1,200 |
| ADU design & blueprints | $8,500 - $15,000 |
| Permit application & city approvals | $2,500 - $6,500 |
How long does ADU permitting take in San Jose?
Typical turnaround is 3 to 6 months from submittal to issued permit, depending on whether soil reports, variances, or HOA reviews are involved. East San Jose parcels with former agricultural use can add 3 to 4 weeks for county soil sign-off. Call (971) 497-2402 for an exact timeline on your property.
Do I need an architect and a builder separately for an ADU in San Jose?
No. At Ellery ADU Studio, the drawings, engineering, permit set, and construction are one contract at one written price. Under Haven Standard Clause 5, the scope is locked at signing, so there is no designer-versus-builder gap to point fingers at. Call (971) 497-2402 for a free estimate.
Junior ADU & Interior Conversion in San Jose
Junior ADU and interior conversion work in San Jose typically runs $60,000 to $140,000 all-in, drawings through final inspection, with the range set by whether you’re converting an existing attached space or carving a new unit out of the main house. San Jose’s ranch-era homes often have oversized family rooms, attics, or bonus spaces that convert cleanly into JADUs, but the city requires a separate entrance and, in most cases, a kitchenette with its own utility connections. Our Junior ADU & Interior Conversion service handles the design, the permit set, and the construction under one contract, so the plumbing, electrical, and egress work is coordinated from the first drawing rather than patched together by separate trades.
Room-to-ADU Conversion
Signs you need it
You have a large primary bedroom, den, or bonus room with its own exterior wall, and you want it to function as a rentable or family unit rather than extra living space.
What it costs in San Jose
Interior room-to-ADU conversions in San Jose run $60,000 to $110,000 depending on plumbing distance and whether the existing electrical panel can carry the new load.
How we do it
We assess the existing walls, panel capacity, and egress path, then draw the conversion so the new unit meets San Jose’s JADU requirements without disturbing the main house beyond the work area.
Interior JADU
Signs you need it
You want an attached rental unit or in-law space inside your existing footprint, with a private entrance, kitchenette, and bath, but you don’t want to touch the exterior of the house.
What it costs in San Jose
A full interior JADU in San Jose runs $80,000 to $140,000 when it requires a new bathroom, kitchenette, and separate utility runs.
How we do it
We design the unit to sit entirely within the existing home envelope, run dedicated plumbing and electrical, build the kitchenette and bath, and document every step with photos so you see what was opened and what was closed.
What Junior ADU & Interior Conversion Costs in San Jose
| Item | Typical range in San Jose |
|---|---|
| Room-to-ADU conversion | $60,000 - $110,000 |
| Interior JADU (full kitchenette & bath) | $80,000 - $140,000 |
| Plumbing & electrical upgrades (if needed) | $8,000 - $20,000 |
Can I add a JADU to my San Jose home if I already have a detached ADU?
Yes. San Jose allows one JADU in addition to a detached or attached ADU on the same lot, provided the JADU stays within the existing structure and meets separate-entrance and utility requirements. Call (971) 497-2402 to confirm eligibility for your specific property.
Does a San Jose JADU need its own kitchen?
A JADU requires a kitchenette: a small cooking area with a sink and food-prep counter. Full-size stoves are typically not required, but the unit must have its own utility connections. Call (971) 497-2402 for an exact scope on your home.
ADU Site Prep & Utilities in San Jose
ADU site prep and utilities in San Jose run $25,000 to $70,000 depending on the work: foundation grading, electrical panel upgrades, and utility lateral extensions are the biggest line items. San Jose’s older housing stock, much of it built when the valley was still orchard land, means a surprising number of lots need panel upgrades from 100-amp to 200-amp service before any new unit can be wired. Our ADU Site Prep & Utilities work is priced upfront and performed by our own crews, not subcontracted out, so the foundation, the trenching, and the panel work are all covered under one written contract.
Foundation & Grading
Signs you need it
Your build site is unlevel, sits on former agricultural land, or you’re putting a new detached ADU on ground that has never been engineered for a structure.
What it costs in San Jose
Foundation and grading for a new detached ADU in San Jose runs $15,000 to $35,000, with soil reports on former orchard parcels adding $2,500 to $5,000.
How we do it
We pull the soil report if required, engineer the slab or stem-wall foundation to San Jose’s seismic and soil standards, and grade the site so drainage moves away from both the new unit and the existing house.
Electrical Panel Upgrade
Signs you need it
Your San Jose home still has a 100-amp panel, and the new ADU’s mini-split, kitchen appliances, and lighting will push the load past what the existing service can safely carry.
What it costs in San Jose
Panel upgrades from 100-amp to 200-amp service in San Jose typically run $3,500 to $6,500 including city inspection.
How we do it
We pull the electrical permit, upgrade the panel with PG&E coordination, size the new circuits for summer AC loads, and run the service to the ADU through dedicated conduit rather than sharing the house’s existing circuits.
Plumbing Lateral
Signs you need it
Your ADU needs its own sewer or water connection, and the existing lateral either doesn’t reach the build site or is too small for the added fixture load.
What it costs in San Jose
Plumbing lateral extensions in San Jose run $4,000 to $12,000 depending on trench depth, distance from the main line, and whether the city requires a new cleanout.
How we do it
We trench the line from the main to the new unit, lay the pipe at San Jose’s required depth for frost-free conditions, install a cleanout, and backfill with compacted soil so the yard doesn’t settle over the trench.
What ADU Site Prep & Utilities Costs in San Jose
| Item | Typical range in San Jose |
|---|---|
| Foundation & grading | $15,000 - $35,000 |
| Electrical panel upgrade (100A to 200A) | $3,500 - $6,500 |
| Plumbing lateral extension | $4,000 - $12,000 |
Does my San Jose home always need a panel upgrade for an ADU?
Not always. Some 200-amp panels have spare capacity, but most San Jose homes built before 1980 have 100-amp service that cannot carry a second full dwelling unit. We assess the panel as part of every free estimate. Call (971) 497-2402 to schedule yours.
How long does site prep take before an ADU build can start in San Jose?
Site prep typically runs 2 to 6 weeks depending on soil reports, trenching depth, and PG&E panel coordination. San Jose’s frost-free winters keep the schedule moving year-round. Call (971) 497-2402 for a written timeline on your property.
Brands We Service in San Jose
We specify and coordinate prefab and modular systems from Abodu, Cover, and Dvele, plus Mighty Buildings for panelized construction. If you already have a prefab unit on order or are comparing systems, we fold the brand into our permit set and site prep scope. See our brands for the full list.
Pricing for ADU in San Jose, CA
| Service | Typical range in San Jose |
|---|---|
| Site assessment | $450 - $1,200 |
| ADU design & blueprints | $8,500 - $15,000 |
| Permit application & city approvals | $2,500 - $6,500 |
| Room-to-ADU conversion | $60,000 - $110,000 |
| Interior JADU (full kitchenette & bath) | $80,000 - $140,000 |
| Foundation & grading | $15,000 - $35,000 |
| Electrical panel upgrade (100A to 200A) | $3,500 - $6,500 |
| Plumbing lateral extension | $4,000 - $12,000 |
What pushes prices up in San Jose: former orchard soil reports on East San Jose parcels, 100-amp panel replacements on pre-1980 homes, and deeper trenching for plumbing laterals. Every project at Ellery ADU Studio carries a written price before work starts, per Haven Standard Clause 1, so the number above is the number you get, not a starting point.
Neighborhoods We Serve in San Jose
We work across San Jose, from the larger post-war lots of Berryessa and East San Jose to the established streets of Willow Glen, Cambrian, and Almaden Valley. Scheduling is coordinated from our Bay Area office, and crews serve the entire San Jose area locally.
- Berryessa
- East San Jose
- Willow Glen
- Cambrian
- Almaden Valley
Service Area - Cities Near San Jose
Beyond San Jose, our crews serve the surrounding South Bay cities. We work in Milpitas, CA, Santa Clara, CA, Sunnyvale, CA, and Campbell, CA, with the same written-price standard on every project, no matter the city.
Serving San Jose, CA - Our Local Coverage Area
We’re based in the San Jose area and know this community well. Use the map below to see our service coverage - if you’re nearby, we can almost certainly help.
FAQs About ADU in San Jose
A live person answers calls 24/7 at (971) 497-2402. You won’t reach a voicemail queue or wait for a callback. For in-person assessments, we schedule free estimates across San Jose within days, not weeks, depending on your neighborhood and the scope of the project.
Yes. We submit the full permit application to San Jose’s building department, manage every round of comments, and coordinate any HOA review required by your association. The permit set, the city correspondence, and the final sign-off are all part of the written scope, not a separate fee.
Yes. If the finished ADU is not built to the permitted drawings, we make it right in writing before the project starts. That promise is set out in our contract, not in a marketing brochure. Call (971) 497-2402 to schedule your free estimate and see the documentation for yourself.
What happens when you call
- 1A real person answersNo phone trees - talk to a local adu pro.
- 2You get an upfront price rangeHonest numbers before anyone is dispatched. No surprises.
- 3We come out and measureLicensed & insured, at a time that suits you - the visit and the quote are both free.
- 4You get the price in writingLine-itemed, yours to keep, and nothing starts until you say go.
What San Jose Customers Say
"The rental income has covered the payment since the second month. They were realistic about the numbers rather than optimistic."
- Odette N."They walked us through setbacks and utility capacity before we paid anything, and told us one of our two options was not going to get approved."
- Mireille T."Every allowance was itemised at the start, so the finish selections did not turn into a surprise at the end."
- Benedict H.