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AfterHow Much Does ADU Construction Cost in San Jose?
ADU construction in San Jose typically costs between $106,200 and $259,600 for a complete detached unit in 2026. Most homeowners building a standard 600 to 800 square foot one-bedroom ADU in San Jose should budget $280 to $410 per square foot, all in. The final number depends on whether you’re building a detached unit, converting a garage, or finishing a basement, plus your site conditions and material selections.
Before we get into the numbers, you should know how Bradford Remodeling Co San Jose works: we put a written price in your hand before any work starts, and that number does not move. It’s part of The Garrison Standard, the framework we’ve operated under since 2004, and it’s non-negotiable.
Key Takeaways:
- San Jose ADU construction runs $106,200 – $259,600 for detached units in 2026.
- Cost per square foot: $280 – $410, driven by site prep, foundation work, utility tie-ins, and finishes.
- Garage conversions cost less than detached builds: $35,400 – $94,400.
- San Jose permit fees, school impact fees, and utility connection charges add $15,000 – $40,000+ to any ADU project.
- Bradford Remodeling provides a written price before work starts and backs every ADU with the 365-Day Done Right Promise.
ADU Construction Cost Breakdown (2026)
Here’s where the money goes on a typical detached ADU in San Jose. These line items reflect what we see on real jobs across Willow Glen, Almaden Valley, Berryessa, Evergreen, and the Rose Garden neighborhoods.
| Cost Component | Typical Range (San Jose, 2026) | Notes |
|---|---|---|
| Design & Engineering | $8,000 – $22,000 | Architectural drawings, structural engineering, Title 24 energy calculations. |
| San Jose Permits & Fees | $12,000 – $30,000 | Building permit, school impact fees, sewer/water connection fees. San Jose charges parkland fees on new square footage. |
| Site Prep & Foundation | $18,000 – $45,000 | Excavation, grading, concrete slab or raised foundation, drainage. Costs rise steeply on sloped lots or poor soils. |
| Framing & Structure | $20,000 – $48,000 | Lumber, shear walls, roof structure. San Jose seismic requirements add engineering and hardware costs. |
| Rough-In: Plumbing, Electrical, HVAC | $14,000 – $35,000 | New water line, sewer lateral, subpanel, mini-split or ducted HVAC. Trenching across the yard is the silent budget killer. |
| Roofing & Exterior | $10,000 – $28,000 | Shingle roof, siding, windows, exterior doors. We install GAF roofing and James Hardie siding as standard. |
| Drywall, Insulation, Paint | $7,000 – $18,000 | R-21 walls, R-38 ceiling. San Jose climate zone requires specific insulation values at inspection. |
| Bathroom | $8,000 – $25,000 | Shower, vanity, toilet, tile, fixtures. We specify Moen and Kohler as standard. |
| Kitchen | $9,000 – $28,000 | Countertops, cabinets, sink, appliance hookups. KraftMaid or Wellborn cabinets, Cambria or Caesarstone surfaces. |
| Finish Carpentry & Trim | $4,000 – $12,000 | Baseboards, door casing, window trim, closet shelving. |
| Final Inspections & Closeout | $2,000 – $5,000 | Building inspection, fire inspection, utility sign-offs, site cleanup. |
Those numbers add up to roughly $112,000 to $296,000 for a ground-up detached ADU. The range we quote most often in San Jose, $106,200 – $259,600, reflects the typical mid-range scope most homeowners actually build: one bedroom, one bath, 500 to 750 square feet, with a kitchen and laundry hookup.
What pushes a project to the top of the range? High-end finishes, site challenges, and scope creep. We’ve seen ADUs that should have cost $140,000 climb past $220,000 because the homeowner kept adding square footage and upgraded every surface after the framing was up. A written scope and a written price, set before demolition starts, is the only defense against that. That is exactly what Bradford Remodeling provides, and it’s the reason The Garrison Standard exists.
What Affects ADU Construction Pricing in San Jose
San Jose is not a cheap place to build. Here are the five or six factors that move your number the most.
- Detached vs. attached vs. garage conversion. A garage conversion runs $35,400 – $94,400 because the foundation, walls, and roof already exist. A detached unit starts from dirt and carries the full cost of new construction. The spread is real, and it’s the single largest decision you’ll make.
- San Jose planning and permit fees. The city charges development impact fees, school fees, and utility connection fees that can total $15,000 – $40,000 on an ADU. This is not a hidden surprise; it is a line item on your permit application. We include it in the written price.
- Slope, soil, and site access. A flat lot in Almaden Valley with easy street access and good soil is a straightforward build. A hillside lot in the East Foothills with 18 inches of clay and a narrow driveway is a different job. Site work in San Jose can swing $20,000 – $50,000 depending on what the excavator hits.
- Utility tie-ins and trenching. Running a new sewer lateral, water line, and electrical service across a 60-foot yard in an older San Jose neighborhood means cutting through established landscaping, patching concrete, and paying trenching costs by the foot. Budget $200 – $400 per linear foot for combined utility trenching.
- Seismic and Title 24 energy requirements. California building code is stricter than anywhere else in the country. San Jose requires shear wall engineering, seismic anchors, and energy compliance that adds both materials and engineering hours. A Title 24 consultant alone runs $1,500 – $4,000.
- Finish level. The difference between a spec-level ADU and a custom one is $80 – $150 per square foot. We install KraftMaid and Wellborn cabinets, Cambria and Caesarstone countertops, Moen and Kohler fixtures. These are traceable brands with manufacturer warranties. If a homeowner wants to upgrade, we price that upgrade in writing before anything is ordered.
How Much Does a Garage Conversion Cost in San Jose?
Converting an existing attached or detached garage into an ADU costs $35,400 – $94,400 in San Jose, which is substantially less than new detached construction. You’re working inside an existing envelope, so you avoid foundation work, framing, and roofing costs.
But garage conversions in San Jose carry their own costs: bringing the slab up to habitable-space standards, insulating walls to Title 24 requirements, replacing the overhead door with a proper wall and window, and upgrading the electrical panel to serve a full kitchen and bath. Many older San Jose homes have 100-amp panels, and a conversion ADU with a kitchen and mini-split will typically require a 200-amp upgrade, which runs $3,000 – $6,000.
How to Save on ADU Construction
Saving money on an ADU in San Jose does not mean cutting quality. It means cutting waste, and waste usually comes from three places: changing your mind after the walls are up, unknowingly paying for a contractor’s inefficiency, and choosing a scope that fights the existing conditions.
- Convert the garage. You can save $50,000 – $120,000 versus a detached build. Same square footage, same function, far less site work.
- Design to standard material dimensions. A 600-square-foot rectangle with an 8-foot ceiling uses lumber, drywall, and roofing with almost no waste. Odd angles and vaulted ceilings create scrap, and scrap is money.
- Lock the scope before the first tool arrives. This is the single biggest money saver we know. A written price, based on a written scope, eliminates surprise invoices. Bradford Remodeling’s written price is the standard on every job, not an optional add-on.
- Keep mechanicals simple. A mini-split for heating and cooling costs less to install than extending central HVAC from the main house, and it works better for a small footprint.
- Choose finishes once, before framing starts. Switching countertop material in month two of a build is not a $500 decision; it is often a $5,000 decision once you account for reordering, re-templating, and scheduling. Our documented brand roster, from KraftMaid to Cambria to Kohler, means you’re choosing from products with real spec sheets and real lead times, not guesses from a showroom.
If you want a precise number for your property, call (669) 272-2637 for a free estimate. We’ll walk your site, review your options, and hand you a written price. No surprises, no pressure.
San Jose ADU Construction Timeline
A detached ADU in San Jose takes 6 to 12 months from the first site visit to final inspection. Here’s a realistic breakdown.
- Design and engineering: 4 – 8 weeks. Your architect or designer produces drawings, then the structural engineer stamps them.
- San Jose plan check: 8 – 16 weeks. The city’s planning and building departments review your submittal. San Jose has streamlined ADU review in recent years, but school district fee processing and utility department sign-offs still add weeks.
- Permit issuance: 2 – 4 weeks. Once plan check clears, you pay fees and pull the permit.
- Construction: 4 – 7 months for a detached ADU. A garage conversion runs 3 – 5 months.
Bradford Remodeling does not run overlapping jobs that slip your start date. When your ADU is on our schedule, the crew is on your site, and the work runs until it is done. At closeout, you get a clean site, a documented scope, and a signed written guarantee in your hand.
FAQ: ADU Construction Cost in San Jose
How much does it cost to build a 500 sq ft ADU in San Jose?
A 500-square-foot detached ADU in San Jose typically costs $140,000 – $205,000, or $280 – $410 per square foot, including permits, utility connections, and finishes. Garage conversions of similar size run $35,400 – $94,400. For a written price on your specific lot, call (669) 272-2637. Estimates are free.
How much does it cost to build a 1200 sq ft ADU in San Jose?
A 1,200-square-foot detached ADU in San Jose runs $336,000 – $492,000 in 2026, assuming the same $280 – $410 per square foot range. Larger ADUs do benefit from some economies of scale on design and permit fees, but site work, utility trenching, and framing scale almost linearly with square footage. Call (669) 272-2637 and we’ll walk you through what size actually fits your budget and your setback requirements.
Is it cheaper to build an ADU or a home addition in San Jose?
An ADU is generally cheaper per square foot than a full home addition. ADU construction in San Jose runs $106,200 – $259,600 for a detached unit, while a home addition of comparable square footage costs $53,100 – $153,400 at the smaller end, climbing fast as you tie into the existing structure, roofline, and HVAC system. But the two are not always interchangeable: an addition expands your existing home, while an ADU creates a separate unit with its own kitchen and entrance, which changes rental value and property tax treatment.
How much does a garage conversion cost in San Jose?
A garage conversion ADU in San Jose costs $35,400 – $94,400, with most one-bedroom conversions landing between $60,000 and $85,000. That includes bringing the slab to code, adding insulation, upgrading the electrical panel, installing a kitchen and bath, and meeting Title 24 energy requirements. Call (669) 272-2637 for a written price on your specific garage.
Can you build an ADU in San Jose for $100k?
A detached ADU under $100,000 in San Jose is unlikely in 2026 once you factor in design fees, permits, utility connections, and site work. A small garage conversion may fall near the bottom of the $35,400 – $94,400 range. The honest answer: for a ground-up detached unit, you should plan for at least $106,200 at the low end, and that assumes a simple site and modest finishes. We will tell you the real number for your property, in writing, before you spend a dollar. Call (669) 272-2637.
Why San Jose Homeowners Choose Bradford Remodeling Co
Most remodeling contractors in San Jose can build you an ADU. The question is whether the price on day one matches the invoice on the final day, and whether anyone picks up the phone when you call with a question at 7:30 in the evening.
Bradford Remodeling Co San Jose operates under The Garrison Standard, the framework set by our parent company, Garrison Partners, established in 2004. What that means in plain terms: a written price before any work starts, every time, with no numbers that move at the door. You sign a scope, you get a price, and that is the price.
Every job is covered by the 365-Day Done Right Promise. If the work fails inside the one-year window, we come back and correct it at no charge. That guarantee is written, not verbal. You get a signed copy at job close, along with a clean site and a documented scope of what was built.
Our crews are background-checked and uniformed. You know who is walking onto your property before they arrive. When you call, a live person answers, 24 hours a day, 7 days a week. No voicemail tree, no callback queue. That matters when you’re in month five of a build and you have a question that can’t wait.
And because we build ADUs and perform ADU construction in San Jose as a core service, not a side job, our material specifications are from a documented roster: KraftMaid and Wellborn cabinetry, Cambria and Caesarstone countertops, Kohler and Moen fixtures, GAF roofing, and James Hardie siding. These brands carry manufacturer warranties that back up our own written guarantee. If you’re looking for a home remodeling contractor that puts the entire job in writing, we’d like to talk.
Get a Written Price for Your San Jose ADU
The best way to know what your ADU will cost is to walk the property with someone who builds them. Bradford Remodeling Co San Jose offers free estimates with no pressure and no obligation. You’ll get a real number, in writing, based on your lot, your scope, and your finish choices.
Call (669) 272-2637 to schedule your free estimate. A live person answers, 24/7.
Written by Curtis Lane, Owner at Bradford Remodeling Co San Jose, serving San Jose and surrounding communities. Curtis has led the company’s San Jose operations under The Garrison Standard since 2004.
Pricing reflects the San Jose market as of 2026. Bradford Remodeling Co San Jose offers free estimates – call (669) 272-2637.
What Our Customers Say
"Respectful crew. Covered the floors and swept every day."
- Jackie T."Painting and drywall repair were flawless. They patched the drywall seams and the paint matches the old wall."
- Cal P."Primary bath redo. Tile is straight, shower pan was flood tested, and the vanity fits perfectly."
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